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HTM 2025 Ventilation in healthcare premises: Design

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1. Anaesthetic Sterile Parallel series Series multi flow multi flow Operating balanced room Disposal hatch a Pass through outer disposal Figure C2 Air flow network HTM 2025 DC reprinted with amendments January 1999 115 Other publications in this series Given below are details of all Health Technical Memoranda available from The Stationery Office HTMs marked are currently being revised those marked t are out of print Some HTMs in preparation at the time of publication of this HTM are also listed 1 Anti static precautions rubber plastics and fabrics t 2 Anti static precautions flooring in anaesthetising areas and data processing rooms 1977 3 4 2005 Building management systems 1996 6 Protection of condensate systems filming aminest 2007 Electrical services supply and distribution 1993 8 2009 Pneumatic air tube transport systems 1995 2010 Sterilizers 1994 1995 1997 2011 Emergency electrical services 1993 12 13 2014 Abatement of electrical interference 1993 2015 Bedhead services 1994 1995 16 17 Health building engineering installations commissioning and associated activities 1978 18 Facsimile telegraphy possible applications in DGHst 19 Facsimile telegraphy the transmission of pathology reports within a hospital a case studyt 2020 Electrical safety code for low voltage systems 1998 Electrical safety code for high voltage system
2. Total flow inwards SI Add mechanical input S2 if necessary to increase SI to give 7 A C per hour Total flow outwards and inwards 4 xl Samce Zour Zin 82 Transfer to WS5 or Eamc Eig Zour 52 Boel Transfer to WS5 HTM 2025 DC reprinted with amendments January 1999 101 Appendix 1 Design of air movement control schemes for operating suites Air Movement Control Worksheet WS 5 R f rence see aa eee T n ies ave ize Summary of air supply and extract for an operating suite i A All door heti Air flow to corridor ee Anaesthetic closed key door open m sec m sec From preparation From operating room OMEN 3r From scrub x E T NN From anaesthetic Suc rans Need teat Rohs gabe f es clesie sec a Th een et Ro Sy pon po Total a Seti Grass a cues E Mr Rete eed ex Y mM 2 S exit Air flow to corridor From other source Total b Structural leakage total c Other room supplies ssec nhe Total air supply atb c d Consider corridor ventilation see table 6 1 a based on 7 A C per hour Air flow required to ventilate corridor Air flow required to ventilate corridor If the air flow from the operating suite a and b is greater than the calculated required volume no furth
3. 4 111 The heat recovery device should be controlled in sequence with the main heater battery and should incorporate a control to prevent the transfer of unwanted heat when the air on condition rises above the required plant set point 4 112 In instances where the plant is cooling the air it may be possible to remove heat from the supply air at high ambient conditions under the dictates of enthalpy comparators in the intake and discharge ducts HTM 2025 DC reprinted with amendments January 1999 45 4 0 Plant equipment selection Attenuation General requirements 4 113 Noise will be generated in an air distribution system by the fan plant items and air flow The ductwork is a very effective transmitter of this noise hence there is generally a need to limit the noise transmission to meet the requirements of the building This normally involves the provision of sound attenuation treatment as part of the overall ductwork system design 4 114 A thorough assessment of the design should be made to assess the noise problem and sound treatment requirements and this should take into account the following primary factors a fan and plant noise generation b air flow generated noise in ductwork fittings and dampers c noise generated at grilles diffusers and other terminals d noise break in and break out of ductwork e cross talk and similar interference f the noise limitations for the building and surrounding areas g ext
4. Frost coil control 5 24 Steam supplied fog frost batteries must be operated as on off devices with their sensor mounted upstream of the battery This will give open loop control a set point of 1 C is recommended 5 25 Low pressure hot water LPHW supplied frost batteries should be controlled using the Proportional mode Their sensor should be located downstream of the battery to give closed loop control A set point of 2 5 C is recommended 5 26 If the temperature downstream of the frost battery as sensed by a serpentine thermostat falls below the required set point over any part of the coil the plant must automatically shut down in order to prevent damage to the other batteries Off plant control 5 27 The control logic must prevent the chiller and pre heater being on at the same time It should also never be possible for the chiller and humidifier to be on at the same time 50 HTM 2025 DC reprinted with amendments January 1999 5 0 Automatic control Humidity control methods and application 5 28 In order to prevent excessive condensation when starting up from a total plant shut down a time delay should be incorporated into the control system such that the humidifier does not start until 30 minutes after the ventilation plant start up 5 29 Irrespective of the method of control a high limit humidistat should be installed to ensure that the condition of the air in the duct does not exceed 70 sat particularly during p
5. HTM 2025 DC reprinted with amendments January 1999 35 4 0 Plant equipment selection 4 22 Organic materials or substances that can support the growth of micro organisms must not be used in the construction of the plant or its distribution system The water fittings and materials directory lists suitable materials for sealants and gaskets 4 23 The plant and its distribution system must not contain any material or substance that could cause or support combustion Vibration 4 24 Vibration from a remote plantroom can be transmitted by the structure of the building may be regenerated and may sometimes be magnified many times Plant should be selected to have the minimum vibration generation and should be installed on suitable anti vibration mounts Pipe and ductwork should incorporate anti vibration couplings preferably in two planes at right angles as close to the vibration source as possible Consideration should also be given to anti vibration pipe hangers and supports Sequence of components 4 25 Generally the following arrangement of plant components should be used although in many instances not all components are required a fresh air inlet b control damper c frost coil d pre filter e silencer f fan g cooler coil h heater coil j humidifier k control damper m final filter There may however be instances where this arrangement is not appropriate and the plant arrangement should be planned a
6. Q Q Q where Q is flow rate from Source 1 m3 s t is the temperature of Source 1 C H is room heat gain kW If the evaluated temperature differences between rooms do not exceed 2 C the solution is satisfactory otherwise proceed as follows i check the assumption on which the heat gains are based ii take steps to reduce the heat gains ii if the door is to a corridor the flow through the open door will be larger than the value given in Table 6 2 Calculate on WS3 assuming it is the key door with door flow unknown and the supply as known iv if the door leads to a room with mechanical supply install a trimmer heater in the supply to the room controlled by either a differential thermostat or a thermostat slaved to the operating room thermostat to ensure that AT is minimised v if the door leads to a room with no mechanical supply increase the door protection flow as follows AT 1 Corus Qoia A These options should be considered in this order and i ii and iii should be investigated thoroughly before proceeding to iv or v The mechanical supply should be increased in exceptional circumstances only and in no case should the supply flow rate to the operating room exceed 1 0 m s 112 HTM 2025 DC reprinted with amendments January 1999 Appendix 1 Design of air movement control schemes for operating suites Relief of excess air from operating room when all doors are closed 1
7. Transfer grille required flow Z or Z C AP Size of transfer grille free area A2 HESS Select larger of A1 or A2 ro mel m 96 HTM 2025 DC reprinted with amendments January 1999 Appendix 1 Design of air movement control schemes for operating suites Air Movement Control Peripheral room eeeesee type parallel multi fiow high low or series multi flow unbalanced Worksheet WS 2c Reference Nominal pressure Pa Consider door from this room to esse open Room pressure now becomes or or mt Pa See table 6 2 Air flow m s Out In Remarks Flow required through open doorway to give protection At above pressures leaks through closed 1 d Pa AP oors are I a EN Structural leaks Total S1 Zour Zin MENU or Ey Zin Zour C Remarks Flow required through open doorway to give protection At above pressures leaks through closed doors are Structural leaks Total S2 Zour Zin NE or E2 Zin Zour LE Consider doors closed Closed doors leakage from table 6 4 T Door to Pa AP Out In Remarks a i and s 1 Structural leaks q Total Return Se and Ep from WS1 Flow through transfer device outward Sp Lour C O cease or or Flow through transfer device inward Er Lin fro
8. 43 As the mechanical supply to the operating room is sized to provide an appropriate flow outward through any door which is opened it follows that when all doors are closed there will be more air supplied to the operating room than can exit from it via leaks etc This excess air can be relieved by either of the two methods following By transfer devices via the anaesthetic room 1 44 For door protection the transfer devices in the anaesthetic room are typically designed to pass 0 47 m sec at a differential pressure of 14Pa When the doors are closed the differential pressure will change to 11Pa and the volume of air passed by the transfer devices will be modified as shown in the following formula Q Q1 AP V AP 20 47x 11 ah 14 0 42 m sec Q excess air to be vented with doors closed Q air flow required for door protection through transfer device AP nominal differential pressure with door to operating cess room closed and door to corridor closed AP nominal differential pressure between either the anaesthetic room and corridor when the operating room door is open or the anaesthetic room and operating room when the corridor door is open This differential pressure is used when selecting size of both devices a If the excess air is less than 0 42 m3 sec a pressure stabiliser is required to ensure that the correct protection air flow is available to pass through the door b If the excess air is greater
9. 50 sa bettas Prep heater AT o c 1 C eee 1 t Set back see 6 10 t 15 C 20 air vol Op room 4 cooling hum off Fireswiteh FS Manual fan Plant room selection Op dept Plant On off Plant room Op dept zh 4 Indication temp ti Op room Indication 96 sat hi Op room 4 Flow alarm flow alarm gt 80 Filter alarm Replace filter L Figure 5 2 Control and indication schedule 54 HTM 2025 DC reprinted with amendments January 1999 5 0 Automatic control PLANT OFF INITIATE START SEQUENCE L O ISOLATION DAMPERS OPEN FROST FOG COIL ON SUPPLY FAN START EXTRACT FAN START ESTABLISH AIR FLOW L O ACHIEVE MIN AIR TEMP 2 C RELEASE HEATER CHILLER HUMIDIFIER TIME DELAY OFF CONDENSATE STAT MADE RELEASE HUMIDIFIER m O PLANT RUNNING MONITORING FUNCTIONS CONTROL FUNCTIONS FROST FOG COIL MINIMUM AIR TEMPERATURE OPERATING ROOM AIR TEMP c4 H Z D H d Hj p Q z HUMIDIFIER HIGH LIMIT 70 OPERATING ROOM HUMIDITY HUMIDIFIER CONDENSATE Table 5 1 Typical plant control algorithm normal start up sequence HTM 2025 DC reprinted with amendments January 1999 55 5 0 Automatic control PLANT RUNNING INITIATE SHUT DOWN DISABLE ALARMS SHUT DOWN HUMIDIFIER START FAN RUN ON TIMER SHUT DOWN CHILLER SHUT DOWN HEATERS SHUT DOWN EXTRACT SHUT DOWN SUPPLY ISOLATION DAMPERS CLOSED PLANT OFF MONITORING FUNCTIONS CONTROL FUNCTIONS FROST PROTECTI
10. 8 5 Kinloss 53 19 26 18 8 5 9 0 Lympne 61 22 28 21 2 1 6 5 Manchester 59 24 31 20 5 2 7 0 Mildenhall 62 22 32 21 5 1 6 5 Pembroke Dock 61 22 29 21 2 2 4 5 Renfrew 55 20 28 19 2 4 8 5 Stornoway 51 18 23 18 0 1 6 5 Turnhouse 54 20 26 19 0 6 10 0 The design enthalpies are values which are exceeded for 10 hours year 0 11 The associated temperature values give the ranges of temperature which occur in association with the design enthalpy values The higher value would be used for the calculation of fabric gains and for sizing air cooled condensers while the lower value is relevant to the design of cooling coils 3 4 The enthalpy figures are also chosen such that they will be exceeded higher in summer lower in winter for only 10 hours in the average year This is a more accurate requirement than the CIBSE recommendation for ordinary buildings 14 HTM 2025 DC reprinted with amendments January 1999 3 0 Assessment of service requirements lt OQ Kinloss o Turnhouse O Aldergrove Driffield o T o Manchester O Mildenhall Q Pembroke Dock Oo Boscombe Down Sw Figure 3 1 Location of sites for outside design values HTM 2025 DC reprinted with amendments January 1999 15 3 0 Assessment of service requirements 16 3 5 For each summer design enthalpy the possible range of temperature dry bulb is quoted All figures quoted are air temperatures and enth
11. Fan location and connection 4 39 Control 4 42 Requirements for particular applications Heater batteries 4 43 General requirements 4 46 Acceptable types 4 48 Location 4 51 Control Cooling coils 4 55 General requirements 4 57 Acceptable types 4 59 Selection 4 60 Location 4 62 Control Contents 4 66 Humidifiers 4 66 General requirements 4 73 Acceptable types 4 78 Selection 4 82 Location 4 84 Control 4 87 Filtration 4 87 General requirements 4 93 Acceptable types 4 99 Selection 4 102 Location 4 104 Control 4 105 Heat recovery 4 105 General requirements 4 109 Location 4 110 Control 4 113 Attenuation 4 113 General requirements 4 120 Acceptable types 4 122 Selection 4 124 Location 4 128 Requirements for particular applications 5 0 Automatic control page 48 5 1 General requirements 5 1 Requirements for automatic control 5 5 Objectives of control system 5 7 Selection of control system 5 10 Location of controls 5 13 Time switching 5 13 Requirements for time switching 5 15 Methods of time switching 5 19 Environmental control 5 19 Temperature control methods and application 5 28 Humidity control methods and application 5 35 Multi zone control methods and application 5 39 Alarms and indication 6 0 Special ventilation systems page 59 6 1 Operating departments 6 1 Special requirements 6 13 Maintenance of room pressures 6 18 Notes on the layout of operating suites 6 19 Standard air movement c
12. It should be the objective when designing a UCV system to achieve levels of less than 10 BCP m when conventional cotton clothing is used so that the use of occlusive clothing or body exhaust systems result in counts of less than 1 BCP m OPERATING ROOM OPERATING WwW 2 a o 2 gt o 2 SIDE SCREENS PLAN OF TYPICAL HORIZONTAL UCV MODULE AIR DISCHARGE FROM EXISTING DIFFUSERS MUST NOT INTERFERE WITH DISCHARGE FROM UCV MODULE DEFLECTOR OR ROOF WILL BE REQUIRED RETURN AIR INLETS Figure 6 4 Typical horizontal UCV modular system HTM 2025 DC reprinted with amendments January 1999 75 6 0 Special ventilation systems Performance of UCV system 6 69 Systems incorporating partial walls only are acceptable but are known to be more susceptible to problems arising from poor operating team discipline occupancy and design parameters than is the case with full walls Choice of system 6 70 Vertical flow systems have a superior performance and are preferred Remote systems will ensure that noise levels are minimal and provide the fewest restraints within the room In addition the handling point equipment can be maintained from outside the operating suite 6 71 n an existing operating department the only solution may be the installation of a modular system The existing primary conditioning plant may require modification to ensure that the standards recommended are achieved 6 72 Horizontal air flow sy
13. a position where exit to an escape route will necessitate passing directly in front of it 6 129 Fume cupboard fans should be installed as near as possible to the termination of the duct thus maintaining the maximum amount of ductwork at negative pressure 6 130 Where there are adjacent buildings with opening windows or where downdraughts occur it may be necessary to increase the height of discharge ducts in order to achieve adequate dispersal In complex locations air flow modelling or wind tunnel tests may be required to determine the optimum height of the stack 6 131 Fume cupboards for certain processes must have separate extract systems however where appropriate individual fume cupboard exhaust systems may discharge via non return dampers into a single collection duct rather than having a large number of separate stacks The collection duct should have a large cross sectional area to minimise its effect on the individual exhaust systems be open to atmosphere upstream of the first connection and be designed to discharge a total air volume at least equal to the combined individual extract systems 6 132 Individual fume cupboard extract systems discharging either directly to atmosphere or into a collection duct do not require duplex fans However a collection duct designed to provide dispersal of effluent from a number of individual extracts should have duplex fans with automatic change over 6 133 Further detailed guidance conc
14. absence of solar gain etc windowless accommodation is acceptable Other spaces appropriate to core areas are those which have only transient occupation and therefore require little or no mechanical ventilation for example circulation and storage areas 6 HTM 2025 DC reprinted with amendments January 1999 2 0 Provision of ventilation in healthcare buildings Natural ventilation 2 4 Natural ventilation is usually created by the effects of wind pressure It will also occur to some extent if there is a temperature difference between the inside and the outside of the building The thermo convective effect frequently predominates when the wind speed is low and will be enhanced if there is a difference in height between inlet and outlet openings Ventilation induced by wind pressures can induce high air change rates through a building provided air is allowed to move freely within the space from the windward to the leeward side 2 5 Asthe motivating influences of natural ventilation are variable it is almost impossible to maintain consistent flow rates and thereby ensure that minimum ventilation rates will be achieved at all times This variability normally is acceptable for general areas including office accommodation general wards staff rooms library seminar rooms dining rooms and similar areas which should be naturally ventilated that is provided with opening windows 2 6 In all cases however heat gain or external noise may preclude n
15. air terminal device is the maximum width of the terminal velocity envelope Drop for a supply air terminal device is the vertical distance between the extremity of the terminal velocity envelope and the air terminal location plane Coanda effect also called ceiling or wall effect is the tendency of an air stream to follow a plane when the stream is in contact with the plane This effect increases throw and reduces drop Isovel a free jet of given momentum which then gives an established velocity profile Velocity pressure pressure inherent in a moving air stream due to its velocity expressed in Pa N m Static pressure pressure insid e the duct which is available to overcome the frictional resistance Total pressure sum of the velocity and static pressures HTM 2025 DC reprinted with amendments January 1999 5 2 0 Provision of ventilation in healthcare buildings General requirements Reasons for ventilation 2 1 Ventilation is essential in all occupied premises This may be provided by either natural or mechanical means The following factors determine the ventilation requirements of a department or area a human habitation fresh air requirements b the activities of the department that is extraction of odours aerosols gases vapours fumes and dust some of which may be toxic infectious corrosive flammable or otherwise hazardous see Control of Substances Hazardous to Health COSHH
16. be required for the scrub area a door between the scrub up room and the operating room is an inconvenience to scrubbed staff and could be replaced by an opening This opening should be larger than a normal single doorway c lay up room if it is intended to lay up instruments in the operating room the preparation room is then used simply as a sterile pack store The nominal room pressure can therefore be the same as that of the operating room and the air flow between the two rooms in either direction Air supplied to the preparation room may be directed into the 62 HTM 2025 DC reprinted with amendments January 1999 6 0 Special ventilation systems operating room thus reducing the required quantity of air supplied directly to the operating room and consequently the total volume required for the necessary air movement control preparation room when the preparation room is used as an instrument lay up room in the traditional way it should be regarded as being of greater cleanliness than the operating room and the design should minimise the transfer of air from the operating room to the preparation room dirty corridor if materials to be disposed of are placed in impervious material for transportation it is not necessary to have a separate corridor for this purpose Standard air movement control schemes 6 19 Air movement control schemes have been developed for several possible operating suite layouts as follow
17. corridor Anaesthetic 3 or 3Pa Preparation lay up 18 Scrub bay and corridor Disposal 12 Preparation sterile pack store 8 Operating room and anaesthetic Preparation lay up 30 room or other series room 17 Pa Disposal 9 with double doors Preparation sterile pack store 22 Operating room and disposal room Or 25Pa No change Operating room and preparation room Anaesthetic room and corridor Preparation lay up 30 or other series room with 3Pa Disposal 9 double doors Operating room 17 Preparation room sterile pack 22 store Preparation room corridor 3Pa No change Disposal room corridor Disposal room outer corridor 0 No change 6 14 Air should flow from the cleaner to the less clean areas as shown in Table 6 1 This is fairly easy to achieve by creating room pressure differentials if the doors are closed but once a door is open the pressure differentials are much more difficult to maintain see Table 6 2 This difficulty is caused by the following a when a person passes through a doorway both the passage of the person and the movement of the door flap cause a transfer of air between the areas separated by the door b when a door is left open there is a transfer of air between the two areas separated by the doorway This is caused by air turbulence but is greatly increased by any temperature differential between the areas a 1 4 m wide doorway may allow the transfer of 0 19 m s of air in
18. each direction when there is no temperature difference but when the temperature differential increases to say 2 K the volume transferred may increase to 0 24 m s 6 15 To minimise the airflow between areas of different orders of Cleanliness air movement control schemes must be designed to ensure that excess air flows through the doorway from the clean to the less clean area 6 16 It is not possible to design an air movement scheme within the restraints of the amount of air available that will protect the operating room when two HTM 2025 DC reprinted with amendments January 1999 61 6 0 Special ventilation systems doors are simultaneously opened The design process used here considers that each door is opened in turn and ensures that the direction and rate of air flow through any open doorway is sufficient to prevent any serious back flow of air to a cleaner area Table 6 3 Recommended air flow rates in m3 s through a doorway between rooms of different cleanliness to control cross contamination Room class Dirty Transitional Clean Sterile Sterile Hatch 0 3 0 24 0 18 Single door 0 47 0 39 0 28 O or 0 28 C Double door 0 95 0 75 0 57 O or 0 57 C Clean Single door 0 39 0 28 O or 0 28 C Double door 0 75 0 57 0 or 0 57 C Transitional Single door 0 28 Oor 0 28 C Double door 0 57 Oor 0 57 C Dirty Single door 0 Open single door 0 80 m x 2 01 m high Double door 0 Open double door 1 80 m x 2 01 m h
19. for example the two pressure stabilisers may be made to pass the open door protection air and also control the operating and anaesthetic room pressures with the door closed To achieve this the stabilisers are sized for the flow rate required with one of the doors open but the pressure setting is adjusted to be the value required with the doors closed This is shown in Figure B2 A Flowrate gt t i i i 1 l l P2 P1 Pressure difference Figure B2 Pressure stabilisers performing two tasks Note the size of the unit is chosen to give as nearly as possible the door protection flow A against the pressure difference P1 The stabiliser will be fully open and acting as an orifice The pressure setting of the stabiliser is adjusted to P2 to control the closed door room pressures P2 by passing flow B Door leakage flows 1 40 For an air movement control scheme to work satisfactorily it is essential that the estimates of door gap leakage made at the design stage are closely related to those which are achieved in practice The calculation of gap flows is complicated by the fact that such flows generally fall into the transition region between laminar and turbulent flow and hence do not follow the normal flow equations Leakage flows have been calculated for doors installed to the specification in the CDB Component Data Base The gaps assumed are 4 mm along the bottom 3 mm at the top and sides and 2 m
20. materials Stainless steel GRP or plastic finishes are preferred 4 70 The cleanliness of the water supply is essential for the safe operation of humidifiers Provision should be made for draining down supply pipework and break tanks for periodic disinfection and for periods when they are not required in service 4 71 The addition of treatment chemicals for continuous control of water quality for humidifier air handling units should be avoided Consideration could be given to installing a UV system to control microbiological growth Given the limitations of UV systems however this will require filtration to high quality to ensure the effectiveness of exposure of organisms to the UV irradiation As with all water treatment systems the unit should be of proven efficacy and incorporate UV monitors so that any loss of transmission can be detected 4 72 All humidifiers must be fitted with their own independent drainage system as detailed in paragraphs 4 8 4 13 Acceptable types 4 73 Steam injection manifold type humidifiers are considered suitable for use in health building air conditioning systems 4 74 Steam may be derived from the central steam supply or generated locally either within or adjacent to the humidifier 4 75 The introduction of steam should be by an appliance specially designed to discharge dry steam into the air conditioning system without objectionable noise or carry over of moisture 4 76 During the design stage c
21. minimise the risks of noise nuisance to surrounding buildings contamination and vandalism 3 89 Each intake and discharge point should be protected from weather by louvres a cowl or a similar device 3 90 Louvres should be sized based on a maximum face velocity of 2 m s in order to prevent excessive noise generation and pressure loss 3 91 Any space behind or under louvres or cowls should be tanked and drained if there is a possibility of moisture penetration 3 92 Intake points should be situated away from cooling towers boiler flues vents from oil storage tanks fume cupboards and other discharges of contaminated air vapours and gases and places where vehicle exhaust gases may be drawn in 3 93 The discharge from an extract system must be located so that vitiated air cannot be drawn back into the supply air intake or any other fresh air inlet Ideally the extract discharge will be located on a different face of the building from the supply intake s Where this is not practicable there must be a minimum separation of 4 metres between them with the discharge mounted at a higher level than the intake 3 94 The discharge should be designed and located so that wind speed and direction have a minimal effect on the plant throughput and should be fitted with corrosion resistant weatherproof louvres to protect the system from driving rain with mesh screens of not less than 6 mm and not more than 12 mm to prevent infestation If possib
22. normally be justified 6 41 f a standby plant is required it must be provided with a gas tight damper at its junction with the supply distribution duct so that no back flow can occur Standby plants can become sources of contamination if warm moist air is allowed to stand in them Their design must ensure that this cannot happen 6 42 Dual duct high velocity systems have advantages but are noisy costly and may give rise to unacceptable values of humidity thus single duct low velocity pressure systems are preferred 6 43 Extract grilles should be sited and balanced to promote air movement along the clean and access corridors towards the reception transfer areas This should not affect the air distribution in the operating suite 70 HTM 2025 DC reprinted with amendments January 1999 6 0 Special ventilation systems Sterilizing and disinfecting unit 6 44 Because of high heat gains within this department it is possible that ventilation in excess of 7 air changes per hour may be necessary Sterilizers steam and condensate piping valves etc must be carefully and efficiently lagged and the plant space adequately ventilated Reception 6 45 The aim in these areas is to provide comfortable conditions having regard to the movement control requirements of the department as a whole The number of air changes will depend on the design but 7 per hour should give acceptable conditions Recovery 6 46 The air change rate in the reco
23. of needs from advice on the oversight of estates management functions to a much fuller collaboration for particularly innovative or exemplary projects Enquiries should be addressed to NHS Estates Consultancy Service address as above 117
24. of the building In general the air transfer grilles should not be installed within fire resisting boundaries although if this is unavoidable these should be fitted with fire or smoke dampers 3 155 Where installed transfer grilles should be of the non vision type sized for a maximum face velocity of 1 5 m s HTM 2025 DC reprinted with amendments January 1999 31 3 0 Assessment of service requirements Pressure relief damper size and location 3 156 Pressure relief dampers are required in lieu of air transfer grilles in areas where it is necessary to maintain pressure differentials between adjacent rooms to prevent reversal of air flows for example in operating theatre suites and clean rooms 3 157 Fire precautions for pressure relief dampers are the same as transfer grilles see paragraphs 3 135 3 136 and for sizing criteria refer to Chapter 6 operating departments 3 158 Where installed pressure relief flaps should be of the balanced blade type with fine adjustment of relief pressure settings and should give a seal as tight as practicable when closed Thermal insulation 3 159 Thermal insulation is applied to ductwork to reduce heat exchange and to prevent condensation 3 160 In a duct system the air temperature changes can be significant especially when passing though untreated space and these have the effect of reducing the heating or cooling capacity of the air and of increasing the energy input to the system
25. page 97 Other publications in this series page 116 About NHS Estates page 117 HTM 2025 DC reprinted with amendments January 1999 1 0 Introduction General 1 1 Ventilation is used extensively in healthcare premises for primary patient treatment in operating departments intensive treatment units and isolation suites It is also installed to ensure compliance with quality assurance of manufactured items in pharmacy and sterile supply departments and to protect staff from harmful organisms and toxic substances for example in laboratories 1 2 This edition of Health Technical Memorandum 2025 Ventilation in healthcare premises is published in separate sections It is equally applicable to both new and existing sites It gives comprehensive advice and guidance to healthcare management design engineers estates managers and operations managers on the legal requirements design implications maintenance and operation of specialist ventilation in all types of healthcare premises 1 3 Current statutory legislation requires both management and staff to be aware of their collective responsibility 1 4 Ventilation is provided in healthcare premises for the comfort of the occupants of buildings More specialised ventilation will also provide comfort but its prime function will be to closely control the environment and air movement of the space that it serves in order to contain control and reduce hazards to patients and staff from airbor
26. re circulation exhaust in which the air is returned to the air treatment system d transfer exhaust in which air passes from the treated space to another treated space Dampers components inserted into air ducts or used in conjunction with air terminal devices which when activated permit modification of the air resistance of the system and consequently a change complete shut off or control of the air flow rate Dampers can be a multiple leaf comprising a number of opposed or parallel blades b single leaf dampers commonly called splitter dampers having two or more slotted slides C butterfly dampers with two flaps in a V arrangement d iris dampers with inter leaving vanes Fire dampers components which are installed in an air distribution system between two fire separating compartments and are designed to prevent propagation of fire and or smoke They are maintained open until activated by fire or smoke detection Sound attenuators silencers components which are inserted into the air distribution system and designed to reduce noise being propagated along the ducts Air terminal device a device located in an opening provided at the end of the duct to ensure a predetermined motion of air in the occupied space Supply air diffuser a supply air terminal device through which air enters a treated space It usually consists of one or more deflecting blades which produce a reductio
27. regulations c dilute and control airborne pathogenic material d thermal comfort e the removal of heat generated by equipment for example in catering wash up and sterilizing areas and in some laboratory areas f the reduction of the effects of solar heat gains g the reduction of excessive moisture levels to prevent condensation for example Hydrotherapy pools h combustion requirements for fuel burning appliances see BS5376 BS5410 and BS5440 j make up supply air where local exhaust ventilation LEV etc is installed Influences on building layout 2 2 Mechanical ventilation systems are expensive in terms of capital and There is a statutory requirement to running costs and planning solutions should be sought which take mechanically ventilate all enclosed advantage of natural ventilation work spaces 2 3 Itis acknowledged that planning constraints imposed by the building shape and or functional relationships of specific areas will invariably result in some measure of deep planning thus minimising the opportunity for natural ventilation However ventilation costs can be minimised by ensuring that wherever practicable core areas are reserved for rooms that require mechanical ventilation irrespective of their internal or peripheral location Examples are sanitary facilities dirty utilities and those rooms where clinical or functional requirements have specific environmental needs and where for reasons of privacy
28. remote central cooling plants with piped chilled water are preferred In the case of a single plant a multi stage direct expansion cooling coil with refrigerant piped from an adjacent compressor condensing plant could be considered If this option is selected a refrigerant gas detector mounted in the base of the duct and an alarm system audible to the end user will also need to be provided COSHH regulations 24 HTM 2025 DC reprinted with amendments January 1999 3 0 Assessment of service requirements 3 85 Clean dry steam is preferred for humidification provided that the boiler water treatment does not render the steam unusable for direct humidification 3 86 When boiler steam is used a warning notice regarding water treatment must be prominently displayed in the boilerhouse stating that the steam is to be used for humidification in the hospital air conditioning plant and that only approved additives must be used Boiler treatments that comply with the Federal Drug Administration FDA Regulations 21 Part 173 310 and also exclude volatiles are considered suitable 3 87 f a suitable supply of steam cannot be obtained from the steam main a steam generator should be provided locally or a self generating humidifier installed The location of a local steam generator is critical if condensate is to drain back into it Discharge and inlet sizing and location 3 88 Air intakes and discharge points are generally located at high level to
29. structural leakage 108 HTM 2025 DC reprinted with amendments January 1999 Appendix 1 Design of air movement control schemes for operating suites Door opening 1 30 Whereas the resulting pressures are dependent upon the ductwork layout the room relationships and the characteristics of the fan the generalisations shown in Table 6 2 can be used to estimate the change in room pressure when a door is opened 1 31 The key door will be the open double door which leaves the operating room at the highest pressure and or requires the largest air flow This will normally be the door to the anaesthetic room but other doors should be checked using the procedure in Worksheet WS3 Transfer grilles 1 32 These may be used to limit the pressure differences across the closed door of a single flow room or in some instances for protection of a series flow or parallel series flow room They allow air flow in both directions and may not be suitable for all applications 1 33 The free area of a grille is calculated from Q A where Ais free area m 0 84 NAP Q is flow rate m3 s AP is pressure difference Pa The flow through a grille at a different pressure may be found from Q Q AP where Q and AP are original flow and AP differential pressure Q and AP are new flow and differential pressure The transfer grille may be replaced by carefully proportioned door undercuts of the equivalent free area 1 34 The funct
30. than 0 42 m sec a transfer grille will be acceptable because at all times the air flow will exceed the flow required for door protection By pressure stabilisers to the corridor 1 45 If it is undesirable to pass operating room air through the anaesthetic room it may be passed directly to a corridor via a separate pressure stabiliser 1 46 If there is sufficient excess air the transfer grille solution at 1 b above should be adopted as it provides the simplest solution and once set up will require no further maintenance With less excess air it is recommended that the air be passed through the anaesthetic room via the pressure stabilisers as at 1 a above thus keeping the number of pressure stabilisers to a minimum Both these solutions increase the air change rate in the anaesthetic room HTM 2025 DC reprinted with amendments January 1999 113 Appendix 1 Design of air movement control schemes for operating suites Corridor patients staff 3 Anaesthetic Scrub Operating room Prep S P S Tex P M Fire door Outer corridor disposal Figure C1 Plan of operating suite Nucleus plan Two corridor with sterile pack store and disposal hatch 114 HTM 2025 DC reprinted with amendments January 1999 Appendix 1 Design of air movement control schemes for operating suites Transitional Corridor patients staff Pass through Sterile bay semi open Preparation sterile supply store
31. the distribution ductwork 7 4 Test holes for the measurement of air flow will be required at carefully selected points in main and all branch ducts Their positions must be identified at the design stage The test positions should be located in a straight length of duct so that accurate measurement can be made and generally in the following positions a on both sides of the fans and heating and cooling coils for pressure drop measurements b in the main ducts C in all branches d in centrifugal fan drive guards opposite the end of the fan spindle for speed measurements 7 5 The number and spacing of holes at a particular location are given in BSRIA Application Guide 1 75 7 6 The actual location for the measurement point should be chosen a at least 1 5 duct diameters upstream of sources of turbulence such as dampers and bends b if this is not possible 10 diameters downstream of dampers bends or tees and 5 diameters downstream of eccentric reducers c where there is enough space round the duct to insert the pitot tube and take readings d where the duct has a constant cross sectional area 7 7 Test holes for measuring total air flow from a fan should be located either 4 diameters upstream or 10 diameters downstream of the fan HTM 2025 DC reprinted with amendments January 1999 89 7 0 Commissioning Information to be provided 7 8 Itis essential that the designer should pass on his intentions fully to th
32. the field Using this knowledge NHS Estates has developed products which are unique in range and depth These are described below NHS Estates also makes its experience available to the field through its consultancy services Enquiries should be addressed to NHS Estates Department of Health 1 Trevelyan Square Boar Lane Leeds LS1 6AE Tel 0113 254 7000 Some other NHS Estates products Activity DataBase a computerised briefing and design system for health buildings applicable to both new build and refurbishment schemes NHS Estates Design Guides complementary to Health Building Notes Design Guides provide advice for planners and designers about subjects not appropriate to the Health Building Notes series SO Estatecode user manual for managing a health estate Includes a recommended methodology for property appraisal and provides a basis for integration of the estate into corporate business planning SO Concode outlines proven methods of selecting contracts and commissioning consultants Reflects official policy on contract procedures SO Health Building Notes advice for project teams procuring new buildings and adapting or extending existing buildings SO Health Facilities Notes debate current and topical issues of concern across all areas of healthcare provision SO Health Guidance Notes an occasional series of publications which respond to changes in Department of Health policy or reflect ch
33. the sizing of transfer devices The resultant pressures are not critical provided the desired air movement is achieved B An open or semi open bay is considered to be part of the operating room and provided air movement is satisfactory no specific extract is required C 15 AC hr is considered necessary for the control of anaesthetic gas pollution D Supply air flow rate necessary to make up 7 AC hr after taking into account secondary air from cleaner areas E No dilution requirement Temperature control requirements only If it is decided that no flammable anaesthetic gases are to be used neither this nor the antistatic floor need be provided In this case a notice that the theatre suite is not suitable for the use of flammable anaesthetic gases must be prominently fixed at the entrance 60 HTM 2025 DC reprinted with amendments January 1999 6 0 Special ventilation systems Maintenance of room pressures 6 13 When considering the overall air flow movement careful thought needs to be given to the operation of the ventilation system to limit smoke spread in the event of a fire However this is a highly staffed department with a low fire risk load status and these factors need to be recognised when developing the fire strategy Table 6 2 Typical pressures in an operating suite when a given door is open Resultant Effect on other rooms Door open between pressure in these rooms Room Pressure Pa Operating room and
34. to accurately establish the required diversified capacity of the chiller 3 52 Due to the complexity of the calculations and the necessity to perform multiple calculations cooling load calculations computer modelling maybe helpful 3 53 There is however a manual calculation procedure detailed in section Ab of the CIBSE guide and a simplified approximate procedure detailed in Section A9 Annual energy consumption 3 54 Annual energy consumptions of simple heating only ventilation systems are simple to calculate based on supply to external air temperature rise and frequency of occurrence of external temperature data CIBSE Table A2 8 3 55 Air conditioning systems are expensive to operate in terms of energy costs when compared to standard heating systems 3 56 The energy consumption of an air handling unit is dependent upon a external conditions b internal control bands HTM 2025 DC reprinted with amendments January 1999 21 3 0 Assessment of service requirements c volume of air flow d method of zoning and control 3 57 Minimum air volumes are usually fixed by the room loads or fresh air requirements however the designer may increase air flow to some rooms or zones in order to balance loads as detailed in paragraphs 3 70 3 71 3 58 The method of zoning and control can significantly influence energy consumption 3 59 The nature of air conditioning operation that is cooling and reheating for humidity or z
35. trap or a floor gully or channel Layout of plants 4 14 The plant must be arranged so that the majority of items are under positive pressure It is preferable that any item of plant requiring a drain be on the positive pressure side of the fan A recommended layout is given in schematic form in Figure 4 1 4 15 Flexible joints should be provided at fan inlet and outlet connections should be equal in cross section to the points of connection and should not be longer than 200 mm or shorter than 100 mm 4 16 Separate extract plant will generally be required for the area served by each supply plant If applicable energy recovery equipment should be fitted and provision made for the fitting of a grade EU2 panel filter to protect it Provision of dampers 4 17 Motorised non return dampers should be located immediately behind the intake and discharge of each supply and extract system respectively They should be of the opposed blade type opening through a full 90 and must close automatically in the event of power failure or plant shutdown to prevent any reversal of air flow 4 18 The quality of motorised dampers is critical They should be rigid with square connections fitted with end and edge seals of a flexible material and with minimal play in linkages The leakage on shut off should be less than 2 4 19 A manually operated isolating damper should be installed between the main plant and its distribution system to enable the plan
36. w p 450 450 Lights general 300 300 Fabric 150 280 Equipment 100 100 Nett gain 1 000 570 Disposal O people during operation 0 0 Lights general 150 150 Fabric 50 150 Equipment 0 0 Nett gain 200 0 Notes a typical maximum b includes full patient monitoring video monitors diathermy etc To be taken into account for selecting the cooling plant 6 27 This duct should run from the sampling point and either connect into the general extract ductwork system or be provided with its own fan built into the operating theatre surgeon s panel 6 28 Where one supply and extract plant serves two operating rooms the sensors should be located in the common extract duct at a point where there is a representative sample of air from both rooms 6 29 The individual control sensors should be removable to prevent damage during cleaning Wall mounted sensors thermostats and humidistats are not recommended 6 30 Controls should be provided in the air handling plantroom to enable operating department ventilation plants to be closed down when the operating suites are unoccupied 6 31 When in the off mode the control system should ensure that the ventilation plant is automatically reinstated if the space temperature falls below 15 C Theatre ventilation plant control and its status indication for run and stop should also be located at the staff control base HTM 2025 DC reprinted with amendments January 1999 67 6 0 Special ventilation
37. 5 DC reprinted with amendments January 1999 Appendix 1 Design of air movement control schemes for operating suites Pressure stabilisers 1 36 Pressure stabilisers Figure B1 have a steep flow rate differential pressure characteristic They therefore hold the pressure constant over a wide range of flow rates They are useful where requirements exist for accurate room pressure control or rapid shut off on pressure fall 1 37 Because the installation of a grille in association with a stabiliser will seriously alter the operating characteristics it is recommended that a location be chosen to avoid the need for visual screening for example at high level The location should be chosen to minimise the likelihood of damage 1 38 The stabilisers used should be virtually silent in operation adjustable on site maintenance free and of a type which cannot be wrongly inserted They should not be used in external walls or where the pressure difference is less than 10Pa The required size of a pressure stabiliser is dependent on the design pressure difference across it and flow rate through it The manufacturer should provide data relating pressure difference to mean velocity or flow rate per unit area From this the required area can be calculated and then rounded up to the nearest size manufactured or nearest combination of smaller sizes 1 39 t is sometimes possible to arrange for a pressure stabiliser to perform two tasks In an anaesthetic room
38. 6 7 Temperature differences of up to 10 K for winter heating and 7 K for summer cooling must not be exceeded Removal and dilution of waste anaesthetic gases 6 8 Waste anaesthetic gas must be contained and removed by a suitable gas scavenging system Some leakage from the anaesthetic equipment and the patient s breathing circuit will occur with all systems during connection and disconnection and from the interface with the patient The air movement scheme should ensure that this leakage is diluted and removed from the theatre suite 6 9 Air extracted from operating suites should not be recirculated as it may contain these contaminants however an energy recovery system should be fitted in the extract in order to reduce the plant energy consumption HTM 2025 DC reprinted with amendments January 1999 59 6 0 Special ventilation systems 6 10 Itis acceptable for the humidity to swing uncontrolled between 40 and 60 saturation In the unlikely event of flammable anaesthetic gases being used a minimum of 5096 humidity must be maintained within the operating room The set point for the humidity control would therefore be set at 55 x 5906 Dilution of airborne bacterial contaminants 6 11 Supply flow rates for the main rooms of the operating suite are given in Table 6 6 For the other areas where room sizes and activities vary from site to site air change rates are given in Table 6 1 These figures have been found to give sufficient
39. 6 during set back as detailed elsewhere 4 41 Where there is a requirement for stand by fans for example in foul extract systems the system should incorporate an automatic changeover facility activated via an air flow sensor and fault indication should be provided Requirements for particular applications 4 42 Where the system air is explosive aggressive or has a high moisture content the extract fan motor should be located outside the air stream This is generally achieved with axial fans by using a bifurcated unit Heater batteries General requirements 4 43 Fog frost heating coils should not be protected by filters They should therefore be constructed in plain tubing without fins and be as near to the outside as possible to minimise condensation during cold weather Access for cleaning must be provided 4 44 Finned tube coils should be constructed of solid drawn copper pipe generally connected in parallel with aluminium fins In instances where the atmosphere is particularly corrosive copper fins should be used 4 45 Where there is a wet heating system in the areas served the main heater battery should be sized for the ventilation requirements only not for the fabric loss Acceptable types 4 46 Electric water or steam heater batteries may be considered however electric heater batteries are expensive to operate and where there are alternatives their use should be restricted to low power use for example trimmi
40. 93 68 Ducts and panel assemblies 1993 69 Protection 1993 70 Fixings 1993 71 Materials management modular system 1995 72 80 Firecode 81 Firecode fire precautions in new hospitals 1996 82 Firecode alarm and detection systems 1989 83 Fire safety in healthcare premises general fire precautions 1994 85 Firecode fire precautions in existing hospitals 1994 86 Firecode fire risk assessment in hospitals 1994 87 Firecode textiles and furniture 1993 88 Fire safety in healthcare premises guide to fire precautions in NHS housing in the community for mentally handicapped ill people 1986 Health Technical Memoranda published by The Stationery Office can be purchased from SO Bookshops in London post orders to PO Box 276 SW8 5DT Edinburgh Belfast Cardiff Manchester Birmingham and Bristol or through good booksellers SO provide an on demand service for publications which are out of print and a standing order service Enquiries about Health Technical Memoranda but not orders should be addressed to NHS Estates Department of Health 1 Trevelyan Square Boar Lane Leeds LS1 6AE HTM 2025 DC reprinted with amendments January 1999 About NHS Estates NHS Estates is an Executive Agency of the Department of Health and is involved with all aspects of health estate management development and maintenance The Agency has a dynamic fund of knowledge which it has acquired during over 30 years of working in
41. 999 41 4 0 Plant equipment selection the device can be discharged and collected at atmospheric pressure it should be discharged directly to drain 4 80 A local steam generator where used must be fed with potable quality water Additional water treatment to the standard set out above may be required If the humidifier is unused for a period exceeding 48 hours it must automatically drain its water content including that contained in the supply pipework right back to the running main and leave itself empty 4 81 Some generators are of a type that requires regular cleaning and descaling The design must allow for them to be installed such that they can be physically isolated from the air duct in order to prevent contamination of the supply by cleaning agents while this is taking place Location 4 82 Careful siting of the humidifier lance is required to prevent the steam impinging onto the side s of the duct condensing and generating excess moisture 4 83 It is essential to position the humidifier upstream of the final attenuator with at least 1 metre unobstructed air flow downstream Control 4 84 Accurate humidity control can only be provided on single zone systems or multi zone systems with zonal humidifiers In the above systems humidity sensors control the humidifier for low level humidity control and override the temperature controls to open the cooling coil valve for high level humidity control 4 85 Multi zone system
42. Air flow generated noise is often referred to as re generated noise 3 129 The noise level generated by air flow in ductwork is very sensitive to the velocity The sound power of this noise is approximately proportional to the sixth power of the velocity that is a doubling of the duct velocity will increase the sound power by a factor of 64 or about 18 dB The duct velocities should therefore be kept as low as possible In general duct fittings which have lower pressure loss factors in similar flow conditions will generate less noise 3 130 Ductwork serving quiet areas should not be routed through noisy areas where noise break in can occur and increase the noise level in the ductwork 3 131 Grille register and louvre noise should be kept to the minimum by selecting types having low noise producing characteristics without high tonal noise and should be fitted with acoustically treated external inlet and outlet louvres Volume control damper locations 3 132 Manually operated balancing dampers are needed generally a in the main duct downstream of the fan b in branches of zone ducts c in sub branch ducts serving four or more terminals d at terminals not covered by c above 3 133 Dampers integral with terminals should only be used for final trimming of air volumes or noise and air distribution problems may ensue 3 134 Dampers in rectangular ducts should be single bladed up to 450 mm longer side and opposed blade multi lea
43. Due to the HEPA filters the discharge from safety cabinets is relatively clean Discharge to outside provides additional safeguards by dilution of any penetrating materials in the event of filter failure In view of the hazard involved it is usually preferable to provide short discharge ducts to atmosphere through a wall or window or through the roof 6 120 Where this is impracticable discharge into the room via a double HEPA filter has been accepted the preferred method however is to discharge above the roofline as per the standard for fume cupboard discharges 6 121 BS5726 permits the installation of microbiological safety cabinets with integral fans provided that the extract ductwork can be kept short that is less than 2 m such an installation however is likely to be noisy and is not recommended for use in new buildings 6 122 Roof level discharge wherever practicable is preferred provided that this does not result in extensive and complicated extract ducts since it removes much of the uncertainty over air re entering the building through ventilation inlets and or windows In such an installation the extract fan should be situated separate from the cabinet and close to the discharge outlet to maintain the duct under negative pressure Laminar flow cabinets 6 123 Vertical laminar flow cabinets BS5726 Class II will be required for certain procedures for example media preparation They operate by drawing air from the labora
44. ON px HP E CONDENSATION PROTECTION Se rm RUN PLANT AT SET BACK FROST PROTECTION SEQUENCE Table 5 2 Plant control algorithm normal shut down sequence 56 HTM 2025 DC reprinted with amendments January 1999 5 0 Automatic control PLANT RUNNING INITIATE SET BACK DISABLE ALARMS SHUT DOWN HUMIDIFIER SHUT DOWN CHILLER SET BACK ROOM TEMP 15 C REDUCE SHUT DOWN EXTRACT REDUCE SUPPLY TO 50 PLANT RUNNING SET BACK MONITORING FUNCTIONS i MINIMUM AIR FLOW MINIMUM AIR TEMPERATURE Table 5 3 Plant control algorithm set back sequence HTM 2025 DC reprinted with amendments January 1999 CONTROL FUNCTIONS FROST FOG COIL OPERATING ROOM AIR TEMP 57 5 0 Automatic control PLANT RUNNING SET BACK INITIATE RESTART SUPPLY TO FULL OUTPUT EXTRACT FAN START ESTABLISH AIRFLOW RESET ROOM TEMP SET POINT RELEASE CHILLER HUMIDIFIER TIME DELAY CONDENSATE STAT MADE RELEASE HUMIDIFIER PLANT RUNNING MONITORING FUNCTIONS CONTROL FUNCTIONS FROST FOG COIL OPERATING ROOM AIR TEMP OPERATING ROOM HUMIDITY MINIMUM AIR FLOW p MINIMUM AIR TEMPERATURE HUMIDITY HIGH LIMIT 70 UMIDIFIER CONDENSATE Table 5 4 Plant control algorithm restart from set back 58 HTM 2025 DC reprinted with amendments January 1999 6 0 Special ventilation systems Operating depart
45. Often it is not possible to accurately predict building load variation at the design stage and thus optimum set points cannot be assessed Information provided by monitoring the operation of the plant via a BMS system will enable optimum set points to be established and energy consumptions reduced 48 HTM 2025 DC reprinted with amendments January 1999 5 0 Automatic control Location of controls 5 10 Whether within the plant duct or room sensors should be located to provide accurate measurement of the condition of the air being monitored 5 11 Sensors and control items such as control valves should be located close to the element being sensed or plant item being controlled in order to minimise time lags within the system which may create over shoot of conditions beyond the design envelope and result in additional energy consumption 5 12 Specific activities will require continuous or intermittent mechanical ventilation and where the latter occurs frequently at a high air change rate for example in bathrooms and treatment rooms sufficient prominence in position and type should be given to the local control of this facility to encourage economical use Time switching Requirements for time switching 5 13 Facilities to start set back and stop the plant should be provided in the plantroom Remote start and set back control and indication if required should be provided at a manned staff location for example at the reception or s
46. The heat transmission to and from the surrounding Space can be reduced by effective insulation of the ducts 3 161 Condensation can arise in ductwork systems conveying cooled air and apart from creating conditions conducive to corrosion of ductwork condensation affects the heat and vapour resisting properties of insulating materials themselves and this induces further condensation 3 162 In normal circumstances the insulation thickness for heat resistance is sufficient to prevent surface condensation but in extreme conditions the insulation thickness for vapour resistance may be greater than that for heat resistance When cold ducts pass through areas of high dew point carefully selected vapour barriers should be applied externally to the insulation 32 HTM 2025 DC reprinted with amendments January 1999 4 0 Plant equipment selection The Building Standards Scotland Regulations and Scottish Home and Health Department Fire Safety New Health Buildings in Scotland HMSO 1987 see letter reference SHHDIDGM 1988 61 and 1990 67 General requirements Air handling unit construction 4 1 The basic technical requirements of the whole of the ventilation system should meet the requirements of Model Engineering Specification C04 Mechanical ventilation and air conditioning systems and fire precautions should be incorporated in accordance with Firecode 4 2 Guidance is available in HTM 81 and BS5588 Part 9 4 3 The plants shoul
47. Ventilation in healthcare premises Design considerations Health Technical Memorandum 2025 London The Stationery Office Wiki Estates HTM 2025 DC reprinted with amendments January 1999 An Executive Agency of the Department of Health O Crown copyright 1994 1998 Published with permission of NHS Estates an Executive Agency of the Department of Health on behalf of the The Stationery Office Applications for reproduction should be made in writing to The Copyright Unit The Stationery Office St Clements House 2 16 Colegate Norwich NR3 1BQ First published 1994 Reprinted 1998 ISBN 0 11 321752 8 Standing order service Are you making full use of The Stationery Office s Standing Order Service The Standing Order Service is a free monitoring of the publications of your choice from over 4000 classifications in 30 major subject areas We send you your books as they are published along with an invoice With a standing order for class 14 02 017 you can be supplied automatically with further titles in this series as they are published The benefits to you are e automatic supply of your choice of classification on publication no need for time consuming and costly research telephone calls and scanning of daily publication lists e saving on the need and the costs of placing individual orders We can supply a wide range of publications on standing order from individual annual publications to all publications
48. a higher standard of filtration may be justified to reduce the level of staining to internal finishes 42 HTM 2025 DC reprinted with amendments January 1999 Most filter companies no longer supply automatic roll type filter housings although they are continuing to supply replacement filters for existing installations 4 0 Plant equipment selection 4 90 Filters must be securely housed and sealed in well fitting frames readily accessible for replacement and must be provided with a differential pressure indicator 4 91 Neither the filter media nor any material used in the construction of the filters should be capable of sustaining combustion and the filter media should be such that particles of the media do not detach and become carried away by the air flow 4 92 Acomplete spare set of filters is required to be provided by the contractor at handover Acceptable types 4 93 A grading system based on arrestance and efficiency has been introduced by Eurovent the European Committee of the Manufacturers of Air Handling Equipment and is shown in Table 4 1 4 94 Arrestance is a measure of the total weight of synthetic dust captured by a filter The weight of dust caught is expressed as a percentage of the total weight of dust entering the filter Arrestance provides a good indication of a filter s ability to remove the larger heavier particles found in outdoor air It is used primarily as a measure of the performance of the low
49. alpies and therefore pertain to areas shaded from the sun Items of equipment located in direct sunlight particularly when adjacent to sunlit surfaces will be subjected to higher temperatures Air cooled refrigeration condensers are particularly vulnerable 3 6 Local adjustments such as for height above sea level or other climate peculiarities should be made as appropriate 3 7 Forsummertime temperature and cooling load calculations the effect of orientation and the properties of building materials affect the sol air temperature and effective time details must be obtained before calculations are undertaken Internal design conditions 3 8 A person s feeling of comfort depends on a complex combination of air temperature radiant temperature air movement and humidity together with personal factors such as clothing and activity The non personal factors have been combined together to produce a comfort index referred to as Resultant temperature 3 9 The choice of a suitable resultant temperature for system design resolves itself into choosing that temperature which should give optimum comfort for the occupants concerned taking into account their clothing and level of activity It must be remembered however that unless mechanical cooling is installed the internal air temperature can never be less than the external shade temperature 3 10 Studies have shown that the majority of people will be neither warm nor cool in winter in ro
50. anging NHS operational management Each deals with a specific topic and is complementary to a related Health Technical Memorandum SO HTM 2025 DC reprinted with amendments January 1999 Encode shows how to plan and implement a policy of energy efficiency in a building SO Firecode for policy technical guidance and specialist aspects of fire precautions SO Capital Investment Manual Database software support for managing the capital programme Compatible with Capital Investment Manual NHS Estates Model Engineering Specifications comprehensive advice used in briefing consultants contractors and suppliers of healthcare engineering services to meet Departmental policy and best practice guidance NHS Estates Quarterly Briefing gives a regular overview on the construction industry and an outlook on how this may affect building projects in the health sector in particular the impact on business prices Also provides information on new and revised cost allowances for health buildings Published four times a year available on subscription direct from NHS Estates NHS Estates Items noted SO can be purchased from Stationery Office Bookshops in London post orders to PO Box 276 SW8 5DT Edinburgh Belfast Cardiff Manchester Birmingham and Bristol or through good booksellers Details of their standing order service are given at the front of this publication NHS Estates consultancy service Designed to meet a range
51. as requiring HEPA filters include ultra clean ventilation UCV suites and manufacturing pharmacies Location 4 102 The primary filter will be positioned on the inlet side of the fan downstream from the frost coil It is essential however that when fitted the secondary filter is on the positive side of the fan to prevent air being drawn into the system after the filter and after any item of equipment which could shed particles 4 103 The filter installation must be arranged to provide easy access to filter media for cleaning removal or replacement with side or front withdrawal as required Control 4 104 Differential pressure transducers should be provided to monitor and alarm on excessive filter pressure drop 44 HTM 2025 DC reprinted with amendments January 1999 4 0 Plant equipment selection Heat recovery General requirements 4 105 Where recirculation of air is not permitted for operational reasons there is a significant risk of discharging large quantities of useful energy in extract air Heat recovery must be considered in all ventilation system design to assess the useful value of energy discharged in relation to the cost of recovery of such heat For most systems in healthcare premises either a run around system of heat exchangers a thermal wheel or a plate type unit may be appropriate 4 106 A full economic assessment of the benefits and costs of heat recovery should be carried out prior to inclusion of hea
52. as shown in the plans in Figure 6 1 b door gaps approximate to those given in Component Data Base 4 mm along bottom 3 mm along top and sides 2 mm between double leaves see Table 6 4 C heat gains are similar to those given in Table 6 5 d a trimmer battery is installed in the air supply system to the preparation room e leakage through the structure is kept to a minimum A complete specification is given in Table 6 6 Table 6 4 Leakage flows in m s through closed door gaps Pressure difference Pa Type 5 10 15 20 25 30 40 Single door 0 03 0 05 0 06 0 06 0 07 0 07 0 08 CDB Size 2 4 3 2 6 Double door CDB 0 00 0 08 0 10 0 11 0 12 0 13 0 14 High permanent length 0 004 0 008 0 010 0 011 0 012 0 012 0 013 of 3 mm gap Note CDB Component Data Base see paragraph 6 21 6 22 It is recommended that every effort should be made to adopt one of the schemes described earlier Provided it is possible to comply with the specifications given in Table 6 6 the entire design may adopted otherwise the manual design procedure should be followed Air distribution within rooms 6 23 The method of introducing air into the operating room is of little bacteriological significance at the recommended rates of flow The velocity working zone should be between 0 1 m s and 0 3 m s and diffuser equipment should be selected to avoid dumping 6 24 In the operating room the air terminals must be at high level and should al
53. at 60 saturation at 20 C is not exceeded during the design summer outside conditions Plant arrangement 6 34 Cost analysis has shown that there can be economic advantages in serving each operating suite with independent supply and extract plant There are also operating and thermodynamic advantages to be gained from this arrangement 68 HTM 2025 DC reprinted with amendments January 1999 6 0 Special ventilation systems Table 6 6 b Air movement control specification for standard plans transfer devices Item Specification Plan Location Flow Pressure and flow rate Pa 1a 1b 2a 2b 3 4 5a 5b direction m s Transfer grilles OR AN amp 0 53 14 door AN gt CC c mounted OR e SPS 0 23 22 T X xX or 0 03 5 i Door undercut DC e DI 0 40 25 Ey Pressure relief LU OR 022 10 i dampers wall CC o DI 0 29 8 AS xscge wR mounted SC gt CC 0 22 22 Xo DO d owe DW Pressure OR oAN amp 0 47 TAa Fono Ae eR up ES conse stabilisers AN gt CC wall mounted 0 22 22 d n AES OR gt CC B 0 35 22 A x 0 45 22 2 Notes a If excess OR air is to be routed via AN the pressure setting of AN stabilisers is to be 11 Pa and OR CC stabiliser is then not required b For use when excess OR air is to be passed directly to CC c Plan 3 only use transfer grilles only when excess OR air is to be routed via AN see note d d Plan 3 only use pressure stabilisers only when excess OR air is to be passed dir
54. atural ventilation General extract ventilation systems 2 7 Ageneral extract system will be required in rooms where odorous but non toxic fumes are likely in order to ensure air movement into the space Examples are therapy kitchens and beverage preparation rooms A single fan motor unit should be provided to meet this need Foul extract ventilation systems 2 8 A separate extract system will be required for sanitary facilities lavage areas and dirty utilities using dual motor fan extract units with automatic change over facilities to ensure that these rooms are maintained at negative pressure while the unit is in use 2 9 Lavatories and dirty utilities should have an extract rate of 10 air changes hour Where WCs are located in bathroom spaces the ventilation required for the WC will usually be adequate for the whole space Supply only ventilation 2 10 Mechanical supply ventilation should be provided in areas where it is important to maintain a positive pressure in a room to prevent the ingress of less clean air for example in clean utilities or operating departments Supply and extract ventilation 2 11 Mechanical supply and extract ventilation should be provided in rooms where it is desirable to maintain the room at a neutral pressure at all times such as treatment areas and plaster rooms Comfort cooling 2 12 Cooling is very expensive in terms of energy costs and should be provided only where necessary to maintain a
55. ccordingly Fans General requirements 4 26 The fan should be selected for good efficiency and minimum noise level but the overriding factor should be the selection of a fan characteristic such that the air quantity is not greatly affected by system pressure changes due to filters becoming dirty or external wind effects Acceptable types 4 27 Fans can be of the axial centrifugal cross flow mixed flow or propeller type depending upon the requirements of the system 4 28 Where used centrifugal fans should preferably be of the backward blade type and give an efficiency of not less than 7896 Alternatively where noise 36 HTM 2025 DC reprinted with amendments January 1999 4 0 Plant equipment selection levels are more critical and pressure requirements are lower forward curved blade fans are acceptable For high power applications aerofoil blade fans may be appropriate Selection Forward curved centrifugal fans can 4 29 Generally large ventilation systems will always use centrifugal fans due overload if allowed to handle more air to their efficiency non overloading characteristics and developed pressures than they are designed for 4 30 Alternatively it may be appropriate to use mixed flow fans in high pressure systems 4 31 Axial flow or propeller fans are generally only used in local through the wall systems or systems with low pressure requirements 4 32 Cross flow fans have very low operating efficiencies and
56. ce pressure stabilisers or in some cases carefully sized transfer grilles or door undercuts are recommended here and between the anaesthetic room and corridor and between the operating room and corridor operating room scrub room interface an opening is provided between these rooms The flow of air through the opening provides protection and gives bacterial dilution within the scrub room the air is then exhausted to the corridor via a pressure stabiliser 63 6 0 Special ventilation systems F Corridor E i P t Disposal Anaesthetic Corridor Vd t t CES ds Disposal Anaesthetic Operating room ae Plan 1a Plan 1b Single corridor with sterile pack store Single corridor with lay up DA Door double 3 Supply m s Door single KEY hes Extract m s KL Door mounted transfer grille E Nominal pressure Pa Pressure relief damper Desired airflow Pressure stabilizer Corridor patients staff amp bagged disposal Corridor patients staff amp bagged disposal Vd tt A bn Anaesthetic Corridor Eu mr ee e Corridor Prep Lay up Operating room P A s Link yos Corridor staff amp supplies Corridor staff amp supplies Plan 2a Plan 2b Linked corridor with sterile pack store Linked corridor with lay up Figure 6 1 a Eight suggested air movement control systems 64 HTM 2025 DC reprinted with amendm
57. ce available b fittings are cheaper than those for circular or flat oval ductwork c it can readily be joined to such component items as heating and cooling coils and filters 3 111 When sizing ductwork the designer should take into account w both installation and operating costs b space limitations imposed by the structure and other services c operating noise levels d requirements of regulation at the commissioning stage 3 112 For overall economy and performance the aspect ratio should be close to 1 1 since high aspect ratios increase the pressure loss heat gains or losses and overall cost for example changing the aspect ratio from 1 1 to 1 4 can typically increase the installed cost of the ductwork by 4096 and add 2596 to the heat gains or losses 3 113 Rectangular ducting should not be the first choice for high pressure systems and should be avoided in systems operating at high negative pressures because the strengthening of the flat sides and the sealing requirements necessary to make rectangular ducts suitable for these high pressures are costly 3 114 Circular ducting is preferable for high pressure systems and for systems operating at high negative pressures In the case of the latter additional stiffening rings may be necessary Machine formed spirally wound ducting and a standard range of pressed and fabricated fittings can sometimes make circular ducting more economical particularly in low pressu
58. cess doors are given in DW 142 and are generally provided to give access to a every regulating damper b every fire and motorised damper C filter to facilitate filter withdrawal d both sides of cooling heating coils e humidifiers f fans and to provide access to motors and impellers 3 139 Care should be taken when siting access doors to ensure that no other services to be installed will prevent reasonable access Diffuser and grille selection and sizing 3 140 The effectiveness of all ventilation and air conditioning systems depends on the methods by which air is introduced to and vitiated air is removed from the space The usual results of poor air terminal selection and or positioning are draughts stagnation poor air quality large temperature gradients and excessive noise 3 141 Air can be supplied to a space in a number of ways although any device can be broadly placed into one of two categories that producing a diffused supply or that producing a perpendicular jet Diffusers may be radial or linear and normally utilise the Coanda effect to reduce the risk of excessive room air movement A perpendicular jet is formed by discharging air through grilles louvres or nozzles which are generally adjustable 3 142 Air flow patterns produced by both types of terminal are dependent to a large extent on the presence of the Coanda effect that is adhesion of the air stream to an adjacent surface 3 143 Supply air ter
59. ck facility to reduce the main supply air volume to 0 35 m3 s by fan control or depending upon the operational policy to isolate the ventilation plant b dirty terminal filter indication and alarm c for modular systems a means of selecting and indicating module running set back off Low air flow indication fan s failure indication d a system purging run up timer minimum 5 minutes linked to the plant start up restart from set back control Noise levels 6 96 The total noise level for a remote plant system within the operating room should be no greater than L 50 dBA For modular systems whether vertical or horizontal flow the maximum noise level should not be more than Lig 55 dBA 6 97 The noise levels apply at the maximum velocity for which the system is designed to operate see Table 3 3 Air terminal 6 98 Vertical flow systems must either be designed to support the operating luminaire system which typically should have a lowest point not less than 2 m above finished floor level FFL or allow the luminaire system to be fixed to the structural soffit of the room 6 99 The plenum chamber and any ductwork downstream of the terminal filter must be clean and of high pressure Class D construction see Figures 6 6 and 6 7 Lighting 6 100 The general lighting in the theatre should give at least 500 lux at the working plane and be as uniform as possible Systems incorporating lighting within the terminal should b
60. comfortable environment for staff and patient or to ensure satisfactory operation of equipment HTM 2025 DC reprinted with amendments January 1999 7 2 0 Provision of ventilation in healthcare buildings 2 13 Summertime temperature calculations using the method mentioned in paragraph 3 40 should be completed for all areas where there is a risk of excessive temperatures Generally air cooling should be provided where these calculations show that without excessive levels of ventilation internal temperatures are likely to rise more than about 3 K above external shade temperatures In these circumstances cooling should commence when the space temperature reaches 25 C Typical areas which may require cooling are some laboratories central wash up and similar areas which are subject to high equipment heat gains Where deep planning of other continuously occupied spaces for example offices is unavoidable there will also be occasions when acceptable levels of comfort can only be maintained by air cooling Planning solutions of this type however will be exceptional and no provision for cooling plant will generally have been included in the Departmental Cost Allowance DCA 2 14 Refrigeration plant should be of sufficient capacity to offset heat gains and maintain areas at a temperature that does not exceed external shade temperatures by more than about 3 K Air conditioning 2 15 Air conditioning is only required in a very small number of a
61. d have a high standard of airtightness The double skin method of construction with insulation sandwiched between two metal faces is recommended 4 4 Theinside of the plant should be as smooth as possible with no channels rolled angles or formed sections that could trap or hold moisture If stiffeners are required they should be fitted externally Internal bracing may be fitted provided it is of a design that will not trap or hold moisture 4 5 Access must be provided adjacent to filters cooling and heating coils heat recovery devices attenuators and humidifiers to facilitate easy cleaning and maintenance see individual plant items 4 6 Airflow across air treatment components such as filters heat exchangers and humidifiers will be influenced by the pattern of the approaching airstream and if unsatisfactory conditions are created the performance of the component will be reduced 4 7 The height of the air handling unit AHU must provide sufficient ground clearance to enable the installation of a drainage system as described below AHU drainage system 4 8 All items of plant that could produce moisture must be provided with a drainage system 4 9 The drip tray should be constructed of a corrosion resistant material and be so arranged that it will completely drain To prevent pooling it is essential that the drain connection should not have an up stand and that a slope of approximately 1 in 20 in all directions should be inc
62. der the dictates of either an off coil temperature sensor or a room temperature sensor depending on the plant configuration and method of control Trimmer heater batteries are generally controlled by one or more averaging temperature sensors within the room or rooms served by the zone 4 53 Various options for control of single and multi zone air conditioning systems are given in section B3 of the CIBSE guide 4 54 Itis usual to open the pre heater and close other heater batteries on system shutdown or fan failure Cooling coils General requirements 4 55 Eliminator plates are required to be fitted downstream of the coil if face velocities exceed 2 25 m s 4 56 Cooling coils will need to be periodically decontaminated The downstream access door should be glazed and have a low voltage weatherproof light fitting provided for maintenance purposes The light fitting should be mounted so that its bulb can be changed from outside the duct Acceptable types 4 57 All cooling coils must be fitted with their own independent drainage system A baffle or similar device must be provided in the drip tray to prevent air bypassing the coil and the tray should be large enough to capture the moisture from the bends and headers 4 58 Where coils are greater than 1 m high intermediate drip trays are required Selection 4 59 Care must be taken in selection to minimise electrolytic action resulting from condensation on the air side Coils construc
63. designed to have a variable velocity over the working zone the velocity decreasing from the centre towards the edge of the terminal In such systems the total air volume should be the same as uniform velocity systems of the same size and should otherwise satisfy the requirements of this guidance document 6 88 When a system is designed to have partial walls with full wall extensions a volume control facility may be incorporated to allow the system to be run with reduced velocity when the demountable full walls are in place It would be the responsibility of the user to ensure correct operation of the system but to assist the user a warning notice should be included on the control panel Filters 6 89 The main plant primary and secondary filters should be to the standards and in the location set out in paragraphs 4 87 4 104 6 90 Terminal filters must be provided within or on the air supply to the unidirectional air flow terminal High efficiency particulate air HEPA filters with a penetration of not greater than 5 when measured against BS3928 Eurovent Grade EU9 will be required 6 91 In some systems the terminal filter is used as a pressure equaliser to balance air flow and filters of greater pressure drop with a lower penetration may be required This is acceptable but there will be penalties in terms of the installed fan power and higher operating noise levels 6 92 The final filters must be installed in a leakproof housing in a
64. determining the summertime temperature is described in section A8 of the CIBSE guide however it is very important to select the time of day and time of year of peak loadings for the calculations which is dependent upon the orientation and proportion of solar to total heat gain 3 41 Where calculations indicate that internal temperatures frequently exceed external shade temperatures by more than 3 K methods of reducing temperature rise should be investigated Options include increasing ventilation rates reducing gains or providing mechanical cooling Peak heating load 3 42 Peak heating load calculations are necessary on all mechanical supply systems to establish the size of heater batteries and subsequently the central plant 3 43 Where ventilation systems provide tempered air to spaces which have supplementary LPHW to offset the building fabric losses the plant heating load should be calculated based on the external winter design temperature selected from Table 3 1 the internal air temperature given in activity data sheets or selected from CIBSE Table A1 3 and the calculated total air volume including a suitable allowance for leakage 3 44 Where the ventilation system is the only means of heating a space an increase in load equivalent to the calculated fabric heat losses from the space should be added to the ventilation load A check of supply temperature difference should be made If it exceeds 1096 the ventilation supply volu
65. difficult both supply and extract may require mechanical means 6 151 Whether natural or mechanical the system should be designed to avoid both horizontal and vertical temperature gradients Both inlet and outlet openings should be placed on opposite or adjacent sides of the building to reduce the effect of wind forces 6 152 Where mechanical air supply is employed electrical interlocks with the boiler plant should be provided to prevent damage in the event of failure of the supply fan s once the air volume is established 6 153 The necessary free opening areas for a naturally ventilated plantroom may be calculated using either the method in A4 of the CIBSE guide or the table in section B13 6 154 A combined natural and mechanical ventilation system should allow for natural extract at high level to take advantage of convective forces in the room with mechanical supply at low level The high level natural ventilators should be sized to cope with the total quantity of ventilation air as above 6 155 To prevent leakage of flue gases and to ensure that the flue draught is not impeded at any time the air pressure in the boiler room must not exceed the prevailing outside pressure Therefore the fan duty should exceed the calculated total combined combustion and ventilation air quantity by at least 25 Fan powered inlets should be arranged to flow outside air into the space at a point where cross ventilation will ensure pick up of heat withou
66. dilution of airborne bacterial contaminants provided the mixing of room air is reasonably uniform Air movement control 6 12 The design of the system should seek to minimise the movement of contaminated air from less clean to cleaner areas Transfer grilles or suitably dimensioned door undercuts enable air to pass in either direction between rooms of equal class and pressure Pressure relief dampers and pressure stabilisers operate in one direction only allow excess air to be directed to the area desired and assist in maintaining room pressure differentials Table 6 1 Hierarchy of cleanliness and recommended air flow rates for dilution of airborne bacterial contaminants Air flow rate for Nominal bacterial contaminant Class Room pressure dilution Pa Flow in Flow out A or supply or extract m3 s m3 s Sterile Preparation room a lay up 35 See Table 6 5 for b sterile pack store 25x5 recommended schemes Operating room 25 and specific values Scrub bay B 25 Clean Central sterile pack store 14 0 10 Anaesthetic room 14 0 15 0 15 Scrub room 14 0 10 Transitional Recovery room 3 15 AC hr C 15 AC hr C Clean corridor 3 D 7 AC hr General access corridor 3 D 7 AC hr Changing rooms 3 7 AC hr 7 AC hr Plaster room 3 7 AC hr 7 AC hr Dirty Disposal corridor 0 E Disposal room 5or 0 0 10 Notes A Nominal room pressures are given to facilitate setting up of pressure relief dampers the calculation process and
67. dings it is the temperature differential between the supply and room air rather than the actual temperature of the supply air which is the critical factor The maximum recommended supply to room air temperature differential is summer cooling 7K winter heating 10K 3 20 Itis also necessary to maintain supply air humidity below 70 in order to minimise risks associated with condensation Air purity 3 21 In healthcare premises the standard of filtration will depend on the activities within the occupied spaces With the exception of special areas for HTM 2025 DC reprinted with amendments January 1999 17 3 0 Assessment of service requirements example manufacturing pharmacies the requirement for aerobiological needs is not stringent and filtration is only required to a maintain hygienic conditions for the health and welfare of occupants or for processes such as food preparation b protect finishes fabrics and furnishings to reduce redecoration costs c protect equipment either within the supply air system that is to prevent blocking of coils or in the space itself to prevent dust collection In these instances an arrestance of 80 to 90 is acceptable requiring an EU3 grade filter Humidity control requirements 3 22 Providing humidification is expensive in terms of plant running costs and maintenance and therefore its use should be restricted to where it is necessary for physiological or operational reason
68. door which lu requires the greatest mechanical flow when open See guidance clause B5 2 Select key door see above Consider this door open room pressure now becomes ae Pa See table 6 2 See B 3 for room pressures Air flow m s In Remarks Flow required through doorway to give protection Air flow out or in via doors transfer devices etc Structural leakage Mechanical extract Mc to WS1 Samc Zout Zin ae transfer Consider all doors closed i Return Se from WS1 O Room pressure now Pa nominal Air flow out or in via door leakage transfer devices etc Pa AP Out in 1 Remarks DEREN Be i _ Structural leakage Mechanical extract amp supply i Total f Flow Zin Zour through transfer device AP aC lp For final selection of transfer device see B7 100 HTM 2025 DC reprinted with amendments January 1999 Appendix 1 Design of air movement control schemes for operating suites Air Movement Control Corridor Worksheet WS 4 Reference Nominal pressure Pa Consider all doors closed Flow required through doorway to give protection Leaks through closed doors transfer devices permanent openings etc Air flow m s Remarks Pa
69. e In such cases only systems with full walls should be used as if the temperature difference is greater than 1 K it will prevent air reaching the operating site A full wall is considered to apply to any wall terminating not more than one metre above the finished floor level 6 58 The term laminar flow is generally misused when discussing UCV systems Commercial systems are available which provide a true laminar flow from the terminal Reynolds No 2000 but this laminar flow will be destroyed due to the disturbance caused by the operating light and personnel Most systems produce the uni directional non laminar flow from the terminal 6 59 The air movement in the operating room as a whole will ultimately depend on a the discharge velocity velocity profile b the provision of full or partial walls c the location of the extract grilles d the supply room air temperature difference 72 HTM 2025 DC reprinted with amendments January 1999 6 0 Special ventilation systems Operating department design consideration 6 60 A UCV system will usually be designed to provide the air conditioning to an individual operating suite and will include primary secondary and terminal filtration and diffusion of air Heating cooling humidification attenuation controls and instrumentation to the standards set out for a conventional operating suite will also be included as part of the installation 6 61 Separate scrub up and disposal fac
70. e commissioning engineer by indicating which parts of the system are high medium and low pressure and by providing a relevant parts of the specification b schematic drawings indicating data listed in Table 7 1 c equipment schedules d controller and regulator schedule e fan performance curves f wiring diagrams for electrical equipment including interlock details Table 7 1 Information to be provided on schematic drawings Items of system Information to be provided Fans Fan total pressure Volume flow rates Motor current Plant items Type and identification numbers from equipment schedules Volume flow rates Pressure losses Dry bulb temperatures Wet bulb temperatures Humidity Dampers including motorised and fire Identification numbers from dampers equipment schedules Location Volume flow rates Location Main and branch ducts Dimensions Volume flow rates and velocities Identification numbers from equipment schedules Terminals Location Dimensions Volume flow rates and velocities Operating pressures Test holes and access panels Location Controllers Set points Notes 1 Fan total pressure is the difference between the total pressure static pressure velocity pressure at the fan outlet and the total pressure at the fan inlet 2 Where volume flow rates are variable maximum and minimum values should be provided 90 HTM 2025 DC reprinted with amendments January 1999 Appendix 1 Design of air movemen
71. e considered 6 101 Specialised task lighting should be provided by thyroidal cruciform or small multiple dome shaped luminaires when vertical air flows are employed as they have good aerodynamic properties The larger typically 1 m diameter HTM 2025 DC reprinted with amendments January 1999 79 08 6661 uenuer sjuawpuawe uM pejuuda Dq SZOZ NLH Figure 6 6 Methods of filter installation FILTER PERFORATED PLATE SIEVE OR OTHER DIFFUSER DEVICE SUPPLY AIR DUCT PLENUM FILTER suiajs s uone nuaA jepeds 0 9 6661 enuer sjuawpuawe yum peyuudei DG SZOZ NLH i8 SUPPLY AIR DUCT POTENTIAL LEAKAGE PATHS DO NOT RESULT IN CONTAMINATION OF PLENUM DIFFUSER Figure 6 7 Methods of filter installation POTENTIAL LEAKAGE PATH WOULD RESULT IN CONTAMINATION OF PLENUM SUPPLY AIR DUCT suiajs s uone nuaA JeDeds 0 9 6 0 Special ventilation systems saucer shaped luminaires supported from a central pillar will occlude the air flow in the critical central zone and are not recommended for vertical flow systems but may be used for horizontal systems where the lamp shape has little influence on the air flow 6 102 Orthopaedic surgery normally requires a broad beam of light from the task lighting theatre luminaire To achieve the best photometric results allowing the surgeon maximum flexibility of the luminaire a minimum of 2 75 m from floor to underside of the diffuser of the UCV system is required t
72. ection and operating pressure control pressure difference and flow rate are from WS2d pressure setting is from WS3 T E T Pressure Flow Free Pressure No Location difference rate area setting Remarks Pa m s Pa es Ds TN 2 HTM 2025 DC reprinted with amendments January 1999 105 Appendix 1 Design of air movement control schemes for operating suites Air movement control in peripheral rooms 1 12 For the design of air movement control three types of air transfer device are considered These are transfer grilles pressure relief dampers and pressure stabilisers Each has a particular field of application within the design as described in paragraphs 1 32 1 39 Air movement is controlled in each of the different room types below Single flow rooms 1 13 An appropriately sized transfer grille should be located in or adjacent to the door of each single flow room to relieve the pressure difference across the door when closed Single flow Parallel multi flow rooms 1 14 The pressure difference across the closed doors must be relieved but transfer grilles are not appropriate where two doors lead to areas of different pressures because reverse flow could occur when the other door is open For this reason pressure relief dampers are used Parallel multi flow Parallel multi flow high pressure room low pressure room 1 15 These rooms will be either high pressure or low pressure with r
73. ectly to CC see notes b and c Table 6 6 c Air movement control specification for standard plans open door air flows Item Specification Plan Location Size Flow and flow rate 1a 1b 2a 2b 3 4 5a 5b direction m s LU OR Single 0 28 ud 5 OR e SPS Single 0 i XD Design flow OR gt DI Single 0 47 rates through OR gt DI Single 0 60 x open doors OR gt SC a O28 7 5 ow X Big a OR gt CC Single 0 39 Note In many OR CC Double 0 75 cases the OR AN Double 0 57 actual flow AN CC Double 0 57 will be greater LU CC Single 0 39 x than this SPS CC Single 0 39 i SCoCC Single 0 39 Woo a DC DI Single 0 A CCoDI Single O28 OR DC Double 0 b X OR gt DC Hatch O o id SPS CC Hatch 0 20 Trimmer LU supply X x heater SPS supply ead Notes a Single opening no door b Fire door c Air lock HTM 2025 DC reprinted with amendments January 1999 69 6 0 Special ventilation systems 6 35 As a general rule if a theatre is out of use but having to be supplied with air from a common plant for more than 25 of the time a separate plant will be preferred In any event it is recommended that a plant or common plant components be limited to supplying two operating suites Ventilation of ancillary areas General 6 36 In order to maintain airflow patterns in the operating suite it is recommended that the whole depar
74. en close and the air will be diverted to the other door When it is considered necessary to protect the scrub room at all times either a transfer grille to the corridor or mechanical extract in the scrub room should be provided Operating room 1 28 Once the peripheral rooms have been considered the operating room requirements may then be decided and the supply flow rate required for air movement control calculated This flow rate should be such that with any one door open the correct air movement directions are maintained There will be one door in the suite which will require the largest supply flow rate to the operating room for protection when open This is called the key door and is discussed separately in paragraph 1 32 below Use of this concept avoids repetitive calculations for each door in turn Having established the required supply flow rate a relief route must be provided to the clean corridor for any excess air when the doors are closed This could be via transfer grilles or pressure stabilisers through a series flow room or via pressure stabilisers to the clean corridor directly Corridors 1 29 All the surplus air from the suite except that lost through structure leakage and any passing to the outer corridor will arrive in the patient staff corridor Should this air be insufficient to achieve the required air change rate see Table 6 1 some additional air supply should be provided The air balance should take account of
75. eneral supply air ceiling diffusers should not discharge directly towards fume cupboards or safety cabinets unless the terminal velocity is such that the airflow pattern of the cabinet is unaffected The design should ensure that high air change rates and or the opening and closing of doors do not have any adverse effect on the performance of safety cabinets or fume cupboards A damped door closure mechanism may help HTM 2025 DC reprinted with amendments January 1999 83 6 0 Special ventilation systems Arrangements for safety cabinet installations 6 117 The manufacture and installation of microbiological safety cabinets must be in accordance with BS5726 and the Code of practice for the prevention of infection in clinical laboratories and post mortem rooms Further information on the selection and installation of these cabinets is contained in Health Equipment Information No 86 A Class 1 microbiological safety cabinet must be specified for routine work involving Group 3 pathogens 6 118 Siting and installation of microbiological safety cabinets are of particular importance because a the protection afforded to the operator by the cabinet depends on a specific and stable uni directional air flow through the open front b the protection afforded to the environment by the cabinet depends on the high efficiency particulate air HEPA filters The exhaust air should never be considered as totally free from microbiological hazard 6 119
76. ents January 1999 Corridor patients staff amp bagged disposal d N Disposal Operating room Possible link corridor Corridor staff amp supplies Plan 3 Linked corridor with external scrub and remote sterile pack store KEY Supply m s bed Extract m s Nominal pressure Pa Desired airflow DMA Door double A Door single 6 0 Special ventilation systems Corridor patients amp staff t t tt NT Anaesthetic 0 1 Fire door Outer corridor disposal Plan 4 Two corridor sterile pack store with disposal hatch Pressure relief damper Pressure stabilizers 4 Door mounted transfer grille Disposal A LION lo Outer corridor disposal Plan 5a Conventional two corridor with sterile pack store Figure 6 1 b HTM 2025 DC reprinted with amendments January 1999 Hatch single Hatch double Corridor patients amp staff Operating room o Plan 5b Conventional two corridor with lay up Outer corridor disposal 65 6 0 Special ventilation systems No mechanical supply or extract ventilation is provided in the scrub room and thus when a door is opened elsewhere in the suite the stabiliser will close allowing the air to be re directed to help protect the doorway 6 21 Any other scheme may be used and the standard solutions applied if the following conditions are met a room layouts in air network terms are
77. er Samc or Eamc to WS1 Consider door to closec Pa At Remarks Closed door leakage Structural leakage Total Flow through transfer grille outward Sp Ef Lour or Flow through transfer grille inward Eg Se Lin Res ad HTM 2025 DC reprinted with amendments January 1999 95 Appendix 1 Design of air movement control schemes for operating suites Air Movement Control Worksheet WS 2b Peripheral room rr type parallel series multi flow Reference Nominal pressure Pa Door from this room to sss ee room of equal cleanliness is not to be protected A transfer grille is located in or adjacent to this door Air flow m s In Remarks Flow required through open doorway to give protection At above pressures leaks through closed doors Pa Mechanical supply extract SE Eg Total X Zour Zin pul or Y Zin Zour O Transfer grille required From high pressure zone NE at APa To low pressure zone Size of transfer grille free area A1 C Consider doors and hatch closed Room pressure becomes ud Pa nominal Closed door leakage from table 6 4 assuming no transfer grille Pa In Remarks Mechanical supply extract Structura leakage Total Air flow required through transfer grille IN OUT Z NN orOUT IN z
78. er grade filters as indicated in Table 4 1 4 95 Efficiency of a filter is measured as the percentage of microscopic particles removed from the air stream by the filter and is used to grade high performance filters as indicated in Table 4 1 Table 4 1 Eurovent filter grades Filter grade Arrestance A Efficiency E 96 1 A 65 2 65 lt A lt 80 3 80 lt A lt 90 4 A gt 90 5 40 lt E lt 60 6 60 lt E lt 80 7 80 lt E lt 90 8 90 lt E lt 95 9 E gt 95 4 96 All filters should be of the dry type Panel filters are cheap and disposable with relatively low dust holding capacity and are generally used as pre filters to eliminate large particles which would otherwise clog or cause damage to the fan and coils 4 97 Where a higher standard of filtration is required secondary bag filters should generally be used 4 98 Where installed as pre filters automatic roll type fabric filters should be of the dry type grade EU2 be operated automatically by an electric motor under the dictates of a pressure differential switch and include a visual indication of the end of the roll All filters develop a higher resistance to air flow with the build up of dirt and this governs the effective life of the filter Filters should therefore be selected for optimum dust holding capacity however this may often only be finally determined from the plant history HTM 2025 DC reprinted with amendments January 1999 43 4 0 Plant equipmen
79. er supply air is necessary Additional air to ventilate corridor Additional air to ventilate corridor Air extract The size of the extract plant should be sized in the order of 1096 below the supply to assist in maintaining the department under positive pressure relative to the outside departments H Extract plant Supply less leakage Less 1096 of supply Total extract Note The extract volume includes 0 15 m sec from the anaesthetic room for a balanced condition 102 HTM 2025 DC reprinted with amendments January 1999 Appendix 1 Design of air movement control schemes for operating suites Room temperatures summer Worksheet WS 6 a Reference Tss a c Find summer supply temperature t s 20 0 828 H O R qo m Note The temperature of a space may be calculated from pan HOt TEE ta Qn 0 828H Where t is temperature of source 1 C Q is flow from source 1 when all doors are closed m s H is heat gain in space kW Flows inwards Temperature C T Check doors to sterile areas Calculated i Maximum Door between room AT AT C L permitted Remarks HTM 2025 DC reprinted with amendments January 1999 103 Appendix 1 Design of air movement control schemes for operating suites Room temperatures winte
80. erature falls below the ambient dew point temperature 3 65 The prediction of surface condensation on building elements such as walls windows and roofs can therefore be obtained by comparing the room dew point and surface temperatures 3 66 Toundertake calculations on the risks of surface condensation it is necessary to estimate the vapour pressure or moisture content of air within the building This will largely be determined by the sources of moisture evaporation within the building that is combustion of gas and other hydrocarbons cooking washing bathing and other processes involving open vessels of hot water and perspiration and respiration of building occupants 3 67 n order to prevent surface condensation occurring it is necessary to provide sufficient ventilation to maintain the maximum ambient dew point temperature below the lowest surface temperature the coldest surface usually being the glazing 22 HTM 2025 DC reprinted with amendments January 1999 3 0 Assessment of service requirements 3 68 Where this would require excessive ventilation levels the designer should consider removal of the moisture at the source of the evaporation via an exhaust hood or similar device 3 69 In intermittently heated buildings it is necessary to consider the condensation risk at night set back conditions as well as during normal operation Calculation methods for this assessment are given in section A10 of the CIBSE guide Calculation o
81. erlocked either so that the supply fan will not operate unless airflow is established within the extract system or vice versa depending on required pressures within rooms being served 5 3 This will be particularly important in laboratory and pharmacy areas that also contain fume cupboards safety cabinets and LEV systems 5 4 Alarms should be provided to show filter fault and low air flow The filter fault alarm should be initiated by a predetermined increase of pressure differentials across the filter The low air flow alarm should be initiated when the supply air quantity falls to 8096 of the design value Objectives of control system 5 5 The primary object of a ventilation or air conditioning plant control system is to maintain the space served within the required environmental control bands at the appropriate times regardless of external conditions or internal loads 5 6 Itis the task of the designer to select a control system to achieve the above with minimum energy consumption Selection of control system 5 7 X Air conditioning plants are both complex to control and expensive in terms of energy costs This makes them ideal for microprocessor or intelligent control 5 8 With developments in building management systems BMS it is often cost effective to provide intelligent controls in lieu of conventional analogue controls for air conditioning plants whether or not there is a general site BMS system 5 9
82. ernal noise generation 4 115 A method of assessment of these factors and the sound attenuation requirements of ductwork systems is given in section B12 of the CIBSE Guide 4 116 The fan is usually the main source of system noise The sound power that it generates varies as the square of the fan pressure and thus to limit the fan noise level the system resistance should be kept as low as economically possible As a general rule the selected fan should operate close to its point of maximum efficiency to minimise its noise generation Where there is disturbance to the air flow at the fan inlet the manufacturer s stated fan noise levels should be increased by up to 5 dB More precise guidance on this aspect may be available from fan manufacturers 4 117 Noise break out from all equipment housed in the plantroom must be taken into consideration if control is to be satisfactory Any ductwork within the plantroom after the silencer should be acoustically insulated to prevent noise break in 4 118 There is no complete means of control over external noise generation from such as road traffic aircraft factory and community noise Consideration must be given to this at the design planning stage 4 119 The Department of Health has issued Health Building Notes Health Technical Memoranda Hospital Design Note No 4 supplemented by Health Circular HN 76 126 and a Data Sheet on Noise and Vibration Control DH 1 2 which should be consulted for detailed
83. erning the selection and installation of fume cupboards is contained in Health Equipment Information No 86 and BS7258 Laboratory fume cupboards published in 1990 Control of extract systems 6 134 It is desirable to provide local control of safety cabinets in order to maximise the life of the HEPA filter and to permit the sealing of the cabinet and room for fumigation if spillage occurs 6 135 To cope with the risk of an accident or spillage outside safety cabinets a panic button should be provided to switch off the supply to that area and discharge all extracted air to atmosphere HTM 2025 DC reprinted with amendments January 1999 85 6 0 Special ventilation systems 6 136 In pathology departments it will be necessary to have one or more microbiological safety cabinets and one or more fume cupboards available for use at all times including weekends Therefore local overriding controls for all these items and any associated ventilation plant will be necessary Plantroom ventilation General requirements 6 137 Plantrooms are required to be ventilated in order to maintain acceptable temperatures for satisfactory operation of the plant and controls and for maintenance activities In the case of plantrooms containing combustion equipment a secondary function of the ventilation air is to provide make up air for the combustion process 6 138 The air required for these purposes should be introduced into the space through inlets p
84. ers must be increase of pressure differential across the filters thereby indicating a dirty installed across filters to give filter maintenance staff a direct indication of their condition 5 43 Visual indication should be provided at a manned staff location for example the reception or staff base and in the plantroom to show plant failure low air flow and filter fault 52 HTM 2025 DC reprinted with amendments January 1999 Symbols Humidity h suffix HL High level 2 Supply Differential temperature Temperature 1 Outside LAF Low air flow Internal Set point X AT FA Flammable anaesthetics t LL Low level FS Fire switch Sample duct X Ir m PPM See ie iu ae Lx y eee RE Koek Extract Figure 5 1 Control system HTM 2025 DC reprinted with amendments January 1999 control panel Operating room v pE fs o me ees o c E co o e ue RE 1 o t s a D 2 5 a o o 5 0 Automatic control c L pcc H 53 5 0 Automatic control T f ji Sl System Control Set point Control Operation status Frost coil tj 5 C t 5C Cooling coil te ty t gt ty Cooling coil hae 60 e sat hy gt 6096 4 es Heating coil t2 tx t2 lt tx Humidifier hLL 40 sat ALL 4096 L 4 m Flammable H dif h 5 h 509 umidifier FA 50 g sat FA X
85. es to adjacent areas 6 54 There are several factors to be considered when designing a UCV system a convection up current from the surgical team the operating lamp and buoyancy effects tend to counter the movement of clean air towards the wound hence the discharge velocity is critical b the size of the operating zone has to be large enough to encompass the operating site and instruments consequently a large area of air diffusion is required typically 7 8 m c the high discharge air velocities and large area of air distribution continue to produce a high discharge air volume and thus recirculation of a considerable proportion of this volume is essential to minimise operating costs 6 55 Because of the size of the uni directional flow terminal and the large volume of air being moved in a relatively small space the siting of the return air grilles can cause short circuiting of the air discharge Partial walls must be provided to control short circuiting 6 56 Return air grilles can be positioned at high level adjacent to the partial wall but the partial wall must be not less than one metre from the operating room wall 6 57 A further factor affecting the air flow pattern is the supply room air temperature difference The supply air temperature should not exceed the general room temperature If the supply air temperature is above room temperature buoyancy effects reduce the volume of air reaching the operating zon
86. espect to the adjacent areas See preparation lay up room in Plan 1b and disposal room in Plan 1b respectively The pressure relief damper is always situated between the room and area which results in the smaller differential pressure to ensure best use of air 1 16 Just as reverse flow can occur if transfer grilles are used it can similarly occur via door gaps when the other door is opened It is not possible to avoid this except by using air locks but due to the low flow rates and short durations involved this is not considered to be of importance Parallel series multi flow rooms 1 17 These rooms are similar to those in paragraph 1 14 above but because the room is of equal cleanliness to one of the adjacent rooms the nominal pressures will be equal and air may flow through the adjoining doorway in either direction for example the prep sterile pack store in Plan 1a Parallel series multi flow Parallel series multi flow 106 HTM 2025 DC reprinted with amendments January 1999 Appendix 1 Design of air movement control schemes for operating suites 1 18 Where the nominal room pressure equals that of the higher pressure adjacent room the best use of air is by supplying air required for bacterial dilution only and allowing this to exhaust via a transfer grille to the area of equal cleanliness The doorway to the lower pressure area is protected by the combination of the supply air and the air which will flow inwards through the transfe
87. f air conditioning parameters in a number of areas consideration should be given to providing separate plants for each area in order to avoid the need for expensive over cooling and reheating of individual areas or zones 5 38 Most multi zone systems within healthcare premises are controlled based on off coil control within the central plant with terminal heater batteries on individual zones Alarms and indication 5 39 Supply and extract systems should include indicator lamps on plantroom control panels to confirm the operational status of each system Where the usage is on a regular daily pattern a time switch control with manual over rider for a limited period should be considered HTM 2025 DC reprinted with amendments January 1999 51 5 0 Automatic control 5 40 Where a system is provided for a particular space the indicator should be in or immediately adjacent to that space and local controls should be provided with labels clearly defining their function 5 41 The plant failure and low airflow alarm should be initiated by a paddle switch or other device located in the main air supply duct This should operate when the air quantity fails to reach or falls to around 8096 of the design value and will give indication of fan failure damper closed access door left open or any other eventuality that could cause a reduction of air quantity 5 42 The filter fault alarm should be initiated by a predetermined Inclined gauge manomet
88. f plant requirements Air supply volumes 3 70 The minimum air supply volume for a room is determined by the greater of the three criteria viz a minimum fresh air requirements paragraphs 3 15 3 17 and However the air supply volume to b minimum supply volume for room loads for heating or cooling individual rooms is often in excess of maximum supply temperature differential paragraphs 3 18 3 20 the minimum volume in order to enable a number of rooms to be supplied at the same temperature that is air volumes are increased to balance the zonal load in terms of energy per unit of supply air volume Wim3 s c specific supply air volumes for dilution ventilation 3 71 Multi zone systems often do not have terminal cooling coils and thus it is often necessary to balance the plant load in terms of cooling energy per unit of supply air volume W m s in order to prevent excessive overcooling and reheating occurring continuously on lightly loaded zones Plant sizing 3 72 Once the air flow has been established as described above the cross sectional area of the air handling unit can be calculated based on a maximum coil face velocity of 2 5 m s 3 73 n order to establish the length of the air handling unit it will be necessary to refer to manufacturers literature ensuring all necessary access panels and components are included as detailed in Chapter 4 3 74 The fan duty should be calculated by adding the resistances of al
89. f type above this size In circular ducts iris type dampers are recommended provided there is enough space round the duct for the damper housing Dampers must be accessible and have a quadrant plate with locking screw Dampers should be located as far away as possible from adjacent branches or plant items HTM 2025 DC reprinted with amendments January 1999 29 3 0 Assessment of service requirements Fire damper types and locations 3 135 Smoke diverting dampers must be provided on recirculation air The Building Standards Scotland systems to automatically divert any smoke contaminated return air to the Regulations and Scottish Home and outside of the building in the event of a fire and arranged so that the Health Department Fire Safety New normally open smoke diverting damper on the return air branch to the input Health Buildings in Scotland HMSO unit closes and all the return air is exhausted through the extract fan 1987 see letter reference SHHD DGM Guidance is available in HTM 81 and BS5582 Part 9 1988 61 and 1990 67 3 136 It is essential that all relevant fire aspects of ducting systems are agreed with the fire officer before the design is finalised Access door locations 3 137 Access doors are required to facilitate access to plant items and ductwork components for inspection maintenance cleaning and replacement and must be of sufficient size to permit access for the required functions 3 138 Recommended locations for ac
90. for calculation and construction tolerances as indicated in Table 3 4 Table 3 4 Typical fan volume and pressure margins Criteria Low pressure Medium high systems pressure systems Volume flow rate margin for leaking and 10 5 balancing requirements Total pressure loss margin a for increase in volume flow rate above 10 5 b for uncertainties in calculation 10 10 Combined total pressure loss margin 20 15 Plantroom size and location 3 80 The ventilation plant and associated equipment should be positioned to give maximum reduction of noise and vibration transmitted to sensitive departments and at the same time achieve an economic solution for the distribution of services 3 81 It is not recommended that noise and vibration generating plant be housed either directly above or below sensitive areas for example operating or anaesthetic rooms unless there is no alternative in which case additional care and attention must be given to the control measures 3 82 The plant must also be located so that it is remote from possible sources of contamination heat gains and adverse weather conditions The design should ensure that wind speed and direction have a minimal effect on plant throughput 3 83 Access to and around plant is essential to facilitate inspection routine maintenance repair and plant replacement Provision of primary services 3 84 Where more than one air handling plant requires cooling
91. guidance Acceptable types 4 120 The noise levels produced by ventilation and other plant should be reduced by using duct silencers These reduce fan noise generated within the duct systems and also control noise break out to the atmosphere It should be noted that duct silencers offer a resistance to air flow The resistance must be included in the fan and ductwork calculations 46 HTM 2025 DC reprinted with amendments January 1999 4 0 Plant equipment selection 4 121 The construction of the sound absorbing in fill should be suitable for the quality of air being handled The duct silencer acoustic in fill should be protected by a perforated sheet metal casing Absorption of moisture dirt and corrosive substances into the in fill and the release of fibrous particles into the airstream should be prevented by the use of a plastic membrane Selection 4 122 Provided care is taken in the design and construction of low pressure systems to avoid significant noise generation in the ductwork attenuation should only be needed to absorb fan noise 4 123 Cross talk attenuators may be necessary where noise intrusion between adjacent spaces can arise and where individual room confidentiality is required Location 4 124 It is always preferable to control noise and vibration at source or as close to source as possible This may be achieved in the equipment specification and selection at the design stage and usually results in a lower cost
92. he rate of evolution is high it is preferable to use local exhaust ventilation systems These tend to give greater control of the substance and minimise the overall ventilation needs Certain substances are regarded as too highly toxic for ventilation control and require devices such as glove boxes Mechanical ventilation systems System selection 2 42 Natural ventilation is always the preferred solution for a space provided that the quantity and quality of air required and the consistency of control of ventilation to suit the requirements of the space are achievable with this method If this is not the case a mechanical ventilation system will be required Choice of central local plant 2 43 Mechanical ventilation is expensive to operate and as such should be controlled to operate when the space being served requires to be ventilated In addition loads on air conditioning plant are rarely constant owing to changes in solar gain occupancy and use of heat generating equipment and lights therefore control of temperature is critical 2 44 If the variation of loads throughout a department or building are in phase or are not significant a central plant with single zone control can be adopted However this is rarely the case and elsewhere the condition or quantity of supply air to different areas or zones of the building must be varied accordingly This can be done by providing either individual plants to each zone or separate zo
93. hould be designed to the same criteria as the main plant To avoid problems with the removal of moisture from the cooling battery it is preferable to effect cooling by means of the primary supply system 6 66 The number of bacteria at the wound site depends on the operating team their discipline and the type of UCV system and choice of clothing Table 6 7 indicates the typical range of values for bacteria carrying particles per cubic metre of air BCP m3 which can be expected at the wound site and shows the combination of clothing and system selection required The maximum recommended standard is 10 BCP m The installed system will be required to meet the performance standard set out in the Validation and verification volume of this HTM Table 6 7 Typical performance of UCV systems for different types of clothing BCP counts expressed as an average over a number of operations Types of clothing Horizontal flow system with walls Vertical flow system Conventional cotton gt 10 BCP m 1 10 BCP m clothing Clothing designed to gt 1 20 BCP m 1 BCP m minimise dispersion of bacteria 74 HTM 2025 DC reprinted with amendments January 1999 6 0 Special ventilation systems 6 67 Horizontal flow systems have been shown to be three to eight times less effective than vertical flow systems and clothing designed to minimise dispersal of bacteria is up to 20 times more effective than conventional cotton clothing 6 68
94. igh Notes A The degree of protection required at an open doorway between rooms is dependent upon the degree of difference in cleanliness between them B Flow rate required between rooms within the same class tends to zero as class reduces C If two rooms are of equal cleanliness no flow is required in practice there will be an interchange in either direction and the design of the air movement will assume zero air flow In certain cases however interchange is not permitted and a protection air flow of 0 28 is assumed in the design for example in the case of a preparation room used as a lay up 6 17 The recommended air flow rates to achieve this are given in Table 6 3 Provided that the dilution criteria in Table 6 1 are met the occasional small back flows created when two doors are opened simultaneously or when there is a high temperature difference across an open door will have little effect on the overall air cleanliness of the affected room Notes on the layout of operating suites 6 18 The following general points should be taken into consideration during the design of operating suites a number of exits the smaller the number of rooms and therefore doorways leading from the operating room the better as traffic is reduced and less complicated air movement control schemes are required b scrub and hand wash facilities these may be a part of the operating room often in a bay Should a separate room
95. ilities are not necessary for air cleanliness where a UCV system is installed although operational policy may prefer such a provision A separate anaesthetic room should however be provided The preparation room sterile store can be shared where the workload permits When a sterile store is provided laying up in the clean zone is preferable bacteriologically 6 62 There is no aerobiological reason why two or more UCV systems should not be installed in a common area as long as adequate spacing is provided but this will require special design considerations and operational discipline Selection of UCV system 6 63 The types of UCV system available are as follows Remote plant systems 6 64 In a remote plant system all the air conditioning equipment is located outside the operating room except for the uni directional air flow terminal the terminal filter and the return air grilles filter see Figure 6 2 EL_3 TO OTHER ROOM IN SUITE PRIMARY A C SECTION RECIRCULATION PRIMARY FILTER UNIT EA EA at V VN AANAANS Puenumanirruser amp DIFFUSER PARTIAL LL FIXED WALL l O l oz me 2 8m min e z lt DEMOUNTABLE Ss WALLS e I d SEE NOTE 2 9 m FIXED CLEARAN OPERATING TABLE Figure 6 2 Typical remote plant UCV system Note Final filters may form part of plenum chamber Modular systems 6 65 Horizontal flow systems are typically of the modular ty
96. ion of the transfer grille is to provide a means of air flow control by which the volume and pressure loss can be established Any method which achieves this for example carefully prepared door undercuts or a simple framed opening is satisfactory If a grille is used it should have an easily removable core to facilitate cleaning Key to figures see paragraphs 1 13 to 1 27 High medium or low pressure H M All other symbols as per key to Figure 6 1 Pressure relief dampers 1 35 Pressure relief dampers have an approximately linear flow differential pressure characteristic but do not have the steep characteristic of the pressure stabiliser see Figure B1 They are therefore not suitable for accurately controlling pressure to a pre set level but may be used to control air volume allowing excess air to vent when not required to protect an open doorway The damper may then be sized to give the desired room pressure at the known flow rate HTM 2025 DC reprinted with amendments January 1999 109 Appendix 1 Design of air movement control schemes for operating suites Pressure relief damper Open wo o E ne LL Shut h Pressure difference Pressure stabiliser w S S Open LL Shut Pressure difference Pressure stabiliser with grille g oO S Open o LL Shut gt Pressure difference Figure B1 Typical flowrate pressure characteristics 110 HTM 202
97. ion systems are merely a combination of a supply and extract system of equal volume and either a single space or a whole building may be considered to be balanced A balanced system is necessary in instances where it is essential to maintain consistent air movement within an area for example treatment rooms Cascade ventilation 2 34 In operating departments it is normal practice to supply air to the operating room and allow it to pass through to less clean areas corridors utility rooms etc from whence it is exhausted Recirculation systems 2 35 Due to the nature of the use of mechanical ventilation systems within healthcare buildings there are few opportunities for the application of recirculation air systems 2 36 Where the designer is considering the installation of a recirculation air system due account must be taken of a minimum fresh air supply volumes b prevention of contamination of supply air from vitiated air in extract systems c prevention of stratification occurring within mixing boxes which may result in freezing of downstream coils d ensuring sufficient velocities through control dampers ideally 5 6 m s to provide suitable authority and good shut off e modulating control of mixing to provide optimum on plant conditions f use of free cooling by cycling the dampers to minimum fresh air when the enthalpy of the outside air is above that of the extract air under conditions when cooling is requi
98. ions are taken the latter may result in an unacceptable level of draughts occurring in winter and possible risk of unacceptable levels of noise transmission 2 28 If individual systems are used the ventilation can be operated intermittently provided it continues to run for at least 15 or 20 minutes after the room is vacated as with light switch operated fans in individual toilets 2 29 f general exhaust systems are used it is recommended that filtered and tempered replacement air is provided via a central supply plant to adjoining lobbies or corridors to prevent the risk of discomfort caused by the ingress of cold air Fire compartmentation requirements must be maintained 2 30 Information on specialist extract systems is given in Chapter 6 10 HTM 2025 DC reprinted with amendments January 1999 2 0 Provision of ventilation in healthcare buildings Mechanical supply systems 2 31 Where mechanical supply systems are required the fresh air should be tempered and filtered before being delivered to the space to avoid discomfort 2 32 The air should be heated using a constant rather than variable temperature source but generally only to the space air temperature In most instances the low pressure hot water heating LPHW should offset any fabric loss so that set back room temperatures can be maintained during unoccupied periods without the need for the ventilation system to operate Balanced ventilation 2 33 Balanced ventilat
99. irements for hospital departments 2 52 Specific requirements for individual spaces and departments are included in the Health Building Notes HBNs and Activity DataBase ADB A Sheets HTM 2025 DC reprinted with amendments January 1999 13 3 0 Assessment of service requirements Selection of design criteria External design conditions 3 1 The most accurate data that is available for the summer and winter conditions at the site should be used 3 2 As virtually all healthcare ventilation systems are full fresh air without recirculation the majority of the load on the air handling plant is in treating the incoming air The plant therefore responds closely to the enthalpy of the outside air and is not influenced to a great extent by other factors 3 3 To improve design accuracy the figures advocated herein Table 3 1 and Figure 3 1 are based on long term frequency distribution of ambient enthalpy Legg and Robertson 1976 The use of simultaneous occurrences of wet and dry bulb temperatures enthalpy avoids errors associated with choosing values from two independent frequency distributions Table 3 1 Outside design values Summer Winter Location Design Associated Design Associated enthalpy temperature enthalpy saturated temperature kj kg DB WB sling kj kg C 8C SC Aldergrove 57 22 27 20 0 1 6 5 Boscombe Down 59 22 30 20 5 2 7 0 Croydon 61 26 29 21 2 2 7 0 Driffield 57 20 28 20 0 4 8 5 Elmdon 58 20 28 20 2 4
100. ise which will allow the overall noise level to be achieved The ventilation plant design noise level is that generated by the plant alone with no other noise source being considered The levels suggested make recognised allowance for the ingress of environmental noise which must be considered in the overall design that is in specifying the attenuation of walls partitions ceilings etc 3 33 The recommended criterion is measured as the a weighted sound pressure level expressed in decibels which should not be exceeded for more than 1096 of the time 3 34 The designer must also consider noise escaping to the external environment and this must not be unacceptable to occupants of adjacent buildings Calculation of building loads Air infiltration 3 35 Air infiltration occurs due to a complex combination of wind pressures and thermal effects operating on a building and is governed by the size and number of openings in the building envelope and the complexity of internal air paths 3 36 Table A4 4 in the CIBSE guide provides formulae for calculation of ventilation for a simple building however in general buildings where it is necessary to accurately calculate infiltration rates solutions can only be obtained by computer modelling 3 37 CIBSE Tables A4 12 and A4 13 give empirical values for typical buildings in normal use in winter For non standard applications the infiltration chart Figure A4 3 with the appropriate correction fact
101. l elements which contribute to the pressure drop of the index circuit 3 75 The main elements which must be considered are a inlet or discharge louvres b plant entry and discharge C attenuators d components within the air handling unit e duct mounted heaters and filters including a dust allowance f ductwork distribution g ductwork fittings including fire dampers volume control dampers bends and sets tees changes of section h air terminal device j discharge velocity 3 76 The pressure drops of louvres grilles external filters and attenuators may be obtained from the selected manufacturers literature HTM 2025 DC reprinted with amendments January 1999 23 3 0 Assessment of service requirements 3 77 Where packaged air handling units are installed the fan pressure drop is usually quoted as external plant resistance and thus the designer does not need to calculate the resistances of individual plant items The designer should however ensure that an allowance has been made for filter clogging and confirm whether the fan pressure quoted is fan total or static pressure 3 78 Resistances of ductwork and fittings may be obtained from the CIBSE guide section C4 however the designer should exercise some care when using tabulated pressure loss information for fittings which are relatively close together 3 79 Upon completion of the resistance calculation exercise the designer should make allowances
102. l be adjustable for rate of flow as well as being easily cleaned and silent in operation Supply terminals will require means of directional adjustment 6 25 Large supply diffusers for example ultra clean style diffusers are particularly prone to buoyancy effects as a result of temperature difference see paragraphs 6 48 6 83 Unless the manufacturer of a proprietary system of this type is able to provide type test data of the performance envelope the installation of these devices is not recommended Automatic control 6 26 Each operating room should have a sampling extract duct for the air conditioning control sensors This should be positioned at normal working height 1 8 m above fixed floor level AFFL and be accessible for cleaning and removal of fluff and lint 66 HTM 2025 DC reprinted with amendments January 1999 6 0 Special ventilation systems Table 6 5 Heat gains and losses assumed in standard solutions Room Item Typical heat gains watts Summer S Winter W Operating 8 people at 150 w p a 1 200 1 200 Lights general 750 750 Lights operating 1 000 1 000 Fabric 250 750 Equipment b 1 000 1 000 Nett gain 4 200 3 200 Preparation 1 person at 150 w p 150 150 Lights general 140 140 Fabric 60 160 Equipment 0 0 Nett gain 350 130 Scrub O people during operation 0 0 Lights general 180 180 Fabric 70 140 Equipment 0 0 Nett gain 250 40 Anaesthetic 3 people at 150
103. lant start up 5 30 With certain types of steam humidifier it may be necessary to install a thermostat in the condensate line from the humidifier s steam supply to ensure that the steam at the control valve is as dry as possible before it is injected into the air supply 5 31 The humidifier and cooling coil control must be interlocked so that they cannot be on at the same time 5 32 The humidifier control system should ensure that it is switched off with the fan It is preferable to design the control system so that the humidifier is isolated for an adequate time before the fan is turned off so as to purge humid air from the system 5 33 All control valves must fail safe that is close in the event of power failure and the humidifier must be interlocked with the low air flow switch 5 34 Suggested humidifier plant control algorithms showing their interrelationship with the rest of the control system are shown in Tables 5 1 to 5 4 Multi zone control methods and application 5 35 Control of all air conditioning parameters is difficult to achieve with multi zone systems since each zone requires reheater and humidifier to give total control of humidity assuming reheat for each zone 5 36 It is therefore usual with multi zone systems to provide control of zonal temperature only with humidity control based on average conditions within all zones or minimum conditions within one zone 5 37 Where there is a requirement for control o
104. ld be provided with a continuous upstand at the rear Each position should have a 1200 mm x 150 mm linear extract grille mounted on a purpose designed plenum box incorporating guide vanes as necessary with its face flush with the upstand The bottom of the grille should be as close as practicable to the level of the working surface usually 75 mm above to allow for cleaning The minimum velocity across any part of the grille should be 1 m s The grille should be readily demountable to allow for cleaning Control of bench extract systems 6 114 Provided that it does not interfere with the operation of the department when not in use the ventilation system for the bench extract and any associated supply can be shut down However a run on timer with a minimum setting of 30 minutes must be provided To this end local control should be provided 6 115 Glutaraldehyde mobile cabinets and work stations development are continuing to take place in the design of systems using glutaraldehyde generally used for the disinfection of scopes These include totally enclosed processing machines to a fume cupboard type of installation Technical requirements and guidance are being developed and will be published when completed Safety cabinet and fume cupboard extract systems Special requirements 6 116 The supply air system should not distort the uni directional and stable air pattern required for fume cupboards and microbiological safety cabinets In g
105. le expansion and a greater angle is necessary internal splitters should be used 3 125 A contraction in a duct section is less critical but the total included angle of the taper should not exceed 40 or 20 where the contraction is made on one side of the duct only 3 126 The most economical way to change the section of a rectangular duct is to restrict the change of duct size to one side only If the calculated reduction or increase to the side dimension is 50 mm or less it is usually not 28 HTM 2025 DC reprinted with amendments January 1999 3 0 Assessment of service requirements economical to change the size at that position The minimum size of a rectangular duct should usually be 150 mm x 100 mm Other fittings 3 127 As a general rule fittings should avoid abrupt changes in direction and sharp edges which cause the flow to separate and form eddies thus limiting pressure loss and noise generation If the fitting leads to the flow preferentially attaching to one side of the outlet then a significant length of straight downstream duct is necessary before the next branch or fitting this length should be greater than five equivalent diameters Noise generation within the ductwork 3 128 Noise is generated in ductwork at sharp edges by tie rods damper blades duct obstructions and sharp bends etc This air flow generated noise becomes an important factor if it is about the same or greater level than the upstream noise level
106. le the inlet duct should slope back towards its intake so that is self draining If this is not practicable it should be provided with a drainage system Heat rejection devices 3 95 The design conditions given in Chapter 2 make no allowance for the elevated temperatures that can occur on the roof of buildings Refrigeration condensers and cooling towers should if practicable be shaded from direct solar radiation or the design adjusted to take account of the gain HTM 2025 DC reprinted with amendments January 1999 25 3 0 Assessment of service requirements 3 96 Air cooled condensers must always be the first choice for heat rejection from any refrigeration plant Evaporative cooling systems must not be used in healthcare premises unless limitations of space mean that they are the only way that the cooling load can be met If they are used the guidance set out in NHS Estates The control of legionellae in healthcare premises a code of practice HTM 2040 must be closely followed Air distribution arrangements Ductwork distribution systems 3 97 Ductwork systems for ventilating and air conditioning applications are referred to by their velocity or pressure category that is as low medium or high velocity or pressure systems HVCA limits are up to 10 m s or 1000 Pa 20 m s or 1750 Pa and 40 m s or 3250 Pa in the case of conventional low medium and high pressure systems respectively High pressure systems are more expensive t
107. logical contamination will be much lower than the general level in a conventional operating room The system should have either fixed partial walls with demountable full wall extensions or fixed full walls down to at least 1 m above FFL 6 76 Horizontal flow systems should have a minimum distance between the side wall panels of 2 4 m The minimum height of the terminal should be 2 1 m These dimensions reflect currently available equipment and may impose operational constraints in addition to a lower level of performance common in these systems Air movement scheme 6 77 There is no strict requirement when using a UCV system to have an air movement control system except in the preparation room 6 78 The inherent feature of a UCV system is its large air flow and it is essential to recirculate air to optimise energy savings 6 79 The fresh air volume should be dispersed via the disposal room and other doors or openings from the operating room as required The anaesthetic room can have balanced ventilation this may be achieved by use of door grilles under cuts or other means 6 80 If preparation rooms are intended to be used for laying up they should have balance ventilation to avoid air transfers interfering with the ultra clean air zone perimeter Discharge air velocities 6 81 To ensure that sufficient air reaches the operating plane the discharge velocity is crucial A number of factors either singly or collectively tend to preve
108. ly and extract WS1 volumes Sd Ed on plan fig C1 5I 4 Define peripheral room types see clauses B2 and B3 and select appropriate Select from worksheets WS2a to WS2e poule e o 5 Locate air transfer devices enter details on worksheets and locate on Selected worksheets figures C1 and C2 from WS2a WS2e I 6 For each peripheral room determine air flows through doors when open and as above calculate mechanical supply or extract and transfer device flows SES 7 Select Key Door and calculate air supply for operating room Does this door produce solution with greatest flow YES Transfer to WS1 and select final rate S and E WS3 El Does Sr to OR exceed 1 0 Reduce Se to 1 0 correct WS1 YES NO Make provision for relief of excess air with doors closed Selected worksheets amp WS3 T p WS4 Calculate supply and extract flow rates for corridor s WS5 I Calculate room temperatures all doors closed and AT s WS6a amp WS6b Do any Ats across doors to sterile rooms exceed 1 0 C YES Rectify as in clause B9 NO Make summary of flows WS6a amp WS6b SE e Size transfer devices size ductwork central plant etc Design ductwork layout control plant etc Figure A1 Air flow design procedures HTM 2025 DC reprinted with amendments January 1999 Appendix 1 Design of air movement control schemes for o
109. m between double leaves Doors should not have wider gaps than these Tighter gaps would HTM 2025 DC reprinted with amendments January 1999 111 Appendix 1 Design of air movement control schemes for operating suites result in lower flow rate requirements and hence lower fan power but care should be taken to ensure that all doors in the suite have similar gap dimensions Room temperature estimation 1 41 The air flow rate required to prevent backflow through an open door is dependent on the temperature difference across the door The design figures shown in Table 6 2 are based upon the temperature differences which will normally occur in practice assuming heat gains and losses in accordance with Table 6 4 1 42 At step 11 of the air flow design process the temperature differences across the doors of all rooms classed as sterile are calculated Worksheet WS6 is recommended for the calculations using the following criteria a assume that the operating room is being controlled at 20 C and calculate the incoming air supply temperature as shown on Worksheet WS6 b the calculation should be repeated for both summer and winter conditions with an operation in progress c assume all doors are closed d use the room supply flow rates from WS1 e use the inward air flows through air transfer devices and closed door leakages from WS2a to WS2e f the formula used in Worksheet WS6 is as follows T 2 Qut Qi QU 0 828H
110. manner which ensures that the filter and its seal can be verified A DOP test will be carried out during commissioning to prove the effectiveness of the complete installation the design must allow access for the introduction of the DOP at least 2 metres upstream of the terminal filter Some manufacturers can provide HEPA filter housings that enable a DIN 1946 housing seal leakage test to be carried out These have the advantage that the test can easily be repeated using simple non specialist equipment as part of the systems monitoring procedures 78 HTM 2025 DC reprinted with amendments January 1999 6 0 Special ventilation systems 6 93 An EU3 grade recirculation return air filter is required to capture relatively coarse particles which could otherwise significantly reduce the life of the final filter Some manufacturers of filters believe that these are not necessary as the larger particles will form a layer on the upstream face of the HEPA filter thus increasing both its efficiency and its capacity 6 94 The design of the system must ensure that all terminal filters are easily accessible for monitoring and maintenance An access point at least 2 m upstream of the terminal filter for the DOP test and a means of monitoring the pressure drop across all filters must be provided Controls and instrumentation 6 95 The controls and instrumentation for the main plant are set out in Chapter 5 UCV systems will additionally require a a set ba
111. me should be increased 20 HTM 2025 DC reprinted with amendments January 1999 3 0 Assessment of service requirements 3 45 If there are multiple heater batteries within a ventilation system the size of each battery will be determined by the desired temperature rise across it Peak cooling load 3 46 Peak cooling load calculations are far more complex than heating load calculations 3 47 n addition to the base data of air flow rates and temperatures when calculating cooling loads the engineer must take into account a solar cooling loads b surface conduction cooling loads c internal gain cooling loads d cooling loads due to high level humidity control e method of control of internal conditions f fluctuations in internal temperatures 3 48 When the peak internal loads have been assessed and a suitable allowance made for non coincidence the supply temperature may be calculated 3 49 Once the lowest required supply temperature of the air handling unit has been established and an allowance made for temperature rise through the fan and ductwork usually 1 K for low pressure systems the off plant enthalpy can be established from a psychrometric chart or table 3 50 The cooling load is calculated from the difference between the internal and external design enthalpies and total air flow 3 51 The cooling loads for all plants on the chilled water system should be calculated at each of the individual peak times in order
112. mental control Temperature control methods and application General 5 19 All control valves must fail safe that is close in the event of power or airflow failure with the exception of the fog frost battery control valve which should open upon power or air flow failure 5 20 A suggested arrangement for controlling heating and cooling batteries is shown in Figures 5 1 and 5 2 Complete plant control algorithms showing their interrelationship with the rest of the control system are shown in Tables 5 1 to 5 4 Room temperature control 5 21 The limits for room temperature set point are generally between 16 C and 25 C depending on the particular application and in some specialised instances for example operating departments are selectable by the user 5 22 The selection of temperature set point for each room or zone may be by a control facility in the room or zone or remotely at the control panel or BMS system The control device should be marked raise and lower and should control within the specified air temperature range with a tolerance of x1 K All other control set points must be selectable in the plantroom and the BMS system where installed 5 23 Where local control is provided an indication of temperature will be required locally or at a staff base if appropriate using an analogue or digital indicator This may be mounted in a supervisory control panel with the signal repeated in the plantroom or on the BMS system
113. ments Special requirements 6 1 The supply of air to an operating room has four main functions a to control the temperature and humidity of the space b to assist the removal of and dilute waste anaesthetic gases C to dilute airborne bacterial contamination d to control air movement within the suite such that the transfer of airborne bacteria from less clean to cleaner areas is minimised 6 2 Functions a b and c are important and must be achieved in full but it is not essential to achieve perfect air movement control d provided that bacterial dilution is adequate 6 3 Terminal or HEPA filters are not generally required 6 4 Because of the complexities of controlling air movement patterns much design effort will be required for this aspect It is important that the design makes the best possible use of the air available as excessive supply air flows for the control of air movement should not be used The maximum air supplied to the operating room should be 1 0 m sec and this air should be distributed evenly within the space usually via ceiling diffusers 6 5 The detailed considerations upon which the supply air flow rate is based are as follows Temperature and humidity control 6 6 Supply flow rates to achieve the required room conditions are calculated conventionally taking account of all heat and moisture gains and losses and of maximum permissible temperature differences between the room and supply air
114. minals can be incorporated into any room surface for example floors walls high or low level desk top etc 3 144 As they operate on the jet principle the use of side wall and linear grilles is restricted to areas where air change rates are low that is less than 10 per hour Linear perforated or rectangular diffusers can provide acceptable 30 HTM 2025 DC reprinted with amendments January 1999 3 0 Assessment of service requirements conditions within the occupied zone at up to 15 air changes per hour In areas where a higher air change rate is required circular diffusers should be used 3 145 The performance of supply air terminal devices is provided based on three criteria throw spread and drop Throw is defined as perpendicular or parallel distance from the terminal to the point at which the air velocity is 0 5 m s isovel Spread is defined as the width of the 0 5 m s isovel and drop is defined as the vertical distance from the centre line of the terminal to the bottom edge of the 0 25 m s isovel 3 146 It is necessary to consider each of these parameters in both summer and winter conditions to ensure satisfactory operation of the air terminal device as warm jets behave very differently from cold jets 3 147 A warm jet tends to rise until it attaches itself to a horizontal surface while a cold jet falls Care must be taken to ensure that this does not lead to unacceptable temperature gradients in winter or excessive air veloci
115. n of the air velocity to a suitable level in the occupied zone a given direction of throw and efficient mixing of the supply air with the air in the treated space May be of the fixed or adjustable type Exhaust grille an air terminal device with multiple passages for the air through which air leaves the treated space May be of the fixed or adjustable type Slot diffuser a diffuser with one or several slots with an aspect ratio of 10 1 or more for each slot Register a combined grille and damper assembly Nozzle an air terminal device designed to generate a low energy loss and thus produce a maximum throw by minimum entrainment 4 HTM 2025 DC reprinted with amendments January 1999 1 0 Introduction Nominal size of an air terminal device is the nominal value of the dimensions of the opening required to mount the air terminal device in Effective area of an air terminal device is the smallest net area used by the air stream in passing through the air terminal device Envelope the geometrical surface of the points of an air jet Throw for a supply air terminal device is the maximum distance between the centre of the core and the extremity of the terminal velocity envelope Induction process by which the primary air entrains secondary air into motion in the room Induction ratio ratio of the combined primary and secondary air flow rate to the primary air flow rate Spread for a supply
116. nd notes are also used to amplify the text c the National Health Service in Scotland Management Executive and they set standards consistent with Departmental Cost Allowances HTM 2025 DC reprinted with amendments January 1999 Contents About this publication 1 0 1 1 1 7 2 0 2 1 2 21 2 42 2 52 3 0 3 1 3 35 Introduction page 3 3 70 General Definitions Provision of ventilation in healthcare buildings page 6 General requirements 2 1 Reasons for ventilation 3 97 2 2 Influences on building layout 2 4 Natural ventilation 2 7 General extract ventilation systems 2 8 Foul extract ventilation systems 2 10 Supply only ventilation 2 11 Supply and extract ventilation 2 12 Comfort cooling 2 15 A Air conditioning 2 17 Specialist ventilation 2 19 q Air scrubbing 2 20 Ventilation for general areas Acceptable methods 2 21 Use of natural ventilation 2 26 Mechanical extract ventilation 4 0 2 31 Mechanical supply systems 4 1 2 33 Balanced ventilation 2 34 Cascade ventilation 2 35 Recirculation systems 2 37 Split comfort air conditioners 2 41 Dilution ventilation Mechanical ventilation systems 2 42 System selection 2 43 Choice of central local plant 4 26 2 46 X Zoning of the building 2 48 Methods of control Specific requirements for hospital departments Assessment of service requirements page 14 Selection of design criteria 3 1 External design conditions 4 43 3 8 Internal design c
117. ne contaminants 1 5 Ventilation systems in themselves present little danger to patients or staff however they do possess the ability to transmit hazards arising from other sources to large numbers of people The danger may not become apparent until many patients and staff have been affected 1 6 The sophistication of ventilation systems in healthcare premises is increasing Patients and staff have a right to expect that it will be designed installed operated and maintained to standards that will enable it to fulfil its desired functions reliably and safely Definitions 1 Air distribution the transportation of air to or from the treated space or spaces generally by means of ducts Air diffusion distribution of the air in a treated space by means of air terminal devices in a manner so as to meet certain specified conditions such as air change rate pressure cleanliness temperature humidity air velocity and noise level Supply air the air flow entering the treated space Exhaust air the air flow leaving the treated space HTM 2025 DC reprinted with amendments January 1999 3 1 0 Introduction Exhaust may be implemented by one or more of the following methods a extraction exhaust in such a manner that the air is discharged into the atmosphere b relief exhaust in such a manner that the air is allowed to escape from the treated space if the pressure in that space rises above a specified level c
118. ne terminal control Where there is a high density of rooms with similar ventilation requirements in an area of a building or department it is usually economical to combine them into a central system 2 45 n large buildings a choice between a single distribution system and multiple smaller systems may arise Large distribution systems and their plant can have the advantage of lower operating costs but require more space for vertical shafts In general very long runs of ducting should be avoided to prevent undue heat losses or gains excessive leakage and difficulties in balancing during commissioning As the pressure losses in the long runs will be greater and a higher initial static pressure will be required this will lead to a more expensive class of ductwork Multiple smaller distribution systems may be more expensive in capital and operating costs but they avoid long runs large ducts and vertical shafts and this may reduce overall building costs 12 HTM 2025 DC reprinted with amendments January 1999 2 0 Provision of ventilation in healthcare buildings Zoning of the building 2 46 The efficiency and effectiveness of any ventilation or air conditioning installation depends largely on the zoning and control of the installation The factors to consider when determining the zoning of a ventilation system for a building or department are a periods of occupancy b fresh air ventilation requirements c smoke control 2 47 Where the ve
119. nents High tonal components from air diffusers etc can seriously disturb concentration over longer periods even when the overall noise level is low Broadband noise causes less annoyance 3 31 The values recommended in Table 3 3 are for the total noise environment of space In general there will be noise transmitted into the space and noise generated within the space The designer requires knowledge of the total hospital layout and operational policies to assign acceptance magnitudes to all the possible noise sources in order to arrive at the correct rating 18 HTM 2025 DC reprinted with amendments January 1999 3 0 Assessment of service requirements Table 3 3 Interior noise level Room Overall noise Ventilation plant Ventilation plant level commissioning design Db A Lio Db A Db A Operating room see 6 96 ultra clean Operating room 50 45 40 conventional Anaesthetic 50 45 40 Preparation 50 45 40 Scrub up 50 45 40 Ward areas 35 30 30 Sanitary facilities 45 40 35 Industrial areas 50 45 40 Circulation areas 50 45 40 3 32 n Table 3 3 the overall noise level takes account of all internal and external noise sources The commissioning noise level is the level measured with a sound level meter in the unoccupied room taking account of the external noise together with the noise generated by the ventilation system When occupied and in use this commissioning level will constitute a continuous background no
120. nes in square bends when used 3 121 The number of duct fittings should be kept to a minimum and there should be a conscious attempt to achieve some standardisation of types and sizes Increasing the number and variety of fittings in a system can markedly raise its overall cost 3 122 Bad design in relation to air flow can lead to vibration of flat duct surfaces increases in duct generated noise and pressure loss unpredictable behaviour in branch fittings and terminals and adverse effects on the performance of installed plant items such as dehumidifying coils Branches 3 123 There are many designs of branch and junction in use The important features are that the flow should be divided or combined with the minimum interference and disturbance Changes in duct sizes should not be made at the branch but a short distance downstream or upstream A good dividing branch design cannot be effective if the flow entering the branch is not uniform across the section Changes of section 3 124 The expansion of a duct section should be formed with sides having a total included angle of no more than 30 and preferably less than 20 If the angle of expansion is greater the flow is not likely to remain attached to the walls of the duct and large eddies will be formed with flow reversal at the walls This leads not only to a high pressure loss but also to a non uniform velocity pattern at the outlet Where there is insufficient space for a gent
121. ng control 4 47 f steam supplied heater batteries are used for example their venting trapping and condensate systems must be designed so that a vacuum cannot occur within the coil and nor will the condensate back up due to excessive back pressure in the condensate main Location 4 48 The standard arrangement of heater batteries in air handling units is given in Chapter 3 38 HTM 2025 DC reprinted with amendments January 1999 4 0 Plant equipment selection 4 49 Where possible wet trimmer heater batteries should be located in plant areas 4 50 Where it is necessary to locate heater batteries in false ceilings etc consideration should be given to the use of electric heaters If this is not practicable drip trays should be installed under both the battery and the control valve assembly to protect the ceiling Control 4 51 Water heater batteries should be connected to a constant temperature heating circuit Fog frost coils should be controlled by an off coil temperature sensor operating a two or three port motorised valve to provide a minimum plant on temperature of between 2 C and 5 C The off coil temperature of the frost coil is generally sensed by a serpentine thermostat laid across the downstream face of the coil or upstream of the next plant item This thermostat will shut the fan down if any part of the air stream is below the minimum set point 4 52 The main heater battery should be controlled in the same manner un
122. nt control schemes for operating suites Air Movement Control Worksheet WS 2e Peripheral room type bay Reference semi open Nominal pressure Pa Note If the room is of the open bay type i e opening is larger than normal single doorway the room should be considered as part of the main room No air movement control considerations need then be made and this sheet can be discarded Supply and or extract flow will be based on air distribution considerations Consider permanent opening Air flow m s Remarks Flow required through opening to give protection Leaks through closed doors to Structural leakage Eamc or flow outward through transfer device Ly Zout Transfer Samc or Eamc to WS1 Transfer device transfer grille O pressure stabilizer Ea Size select transfer device for flow rate m AP pall Note A door from the bay is considered with the peripheral room to which it leads or if it leads to the corridor it is considered with the main room HTM 2025 DC reprinted with amendments January 1999 99 Appendix 1 Design of air movement control schemes for operating suites x E zw Air Movement Control Worksheet WS 3 Operating room Reference Nominal pressure Pa Note To avoid considering each door open in turn the key door concept is introduced This is the
123. nt this a uncontrolled short circuiting b heat emission from the operating lamp c buoyancy effects resulting from the supply room air temperature difference d up current generated by personnel e the movement of staff within the zone 6 82 The minimum discharge velocity is selected to take account of these factors and is greater than the theoretical minimum value 6 83 At the suggested minimum discharge velocity insufficient air will reach the working zone if the supply air temperature is greater than the room air temperature HTM 2025 DC reprinted with amendments January 1999 77 6 0 Special ventilation systems 6 84 The minimum velocity of the discharged air as measured 2 metres above the FFL should be as shown in Table 6 8 Table 6 8 Minimum discharge velocities Vertical flow systems Horizontal flow systems velocity measured 2 m from FFL Full Walls terminating not Fixed Partial Walls Measured 1 m from filter more than 1 m above FFL terminating 2 m above diffuser face these walls may be FFL demountable extensions of the fixed partial wall 0 40 m s 0 3 m s average 0 38 m s average 6 85 The minimum discharge velocity measured 1 m above FFL for vertical flow systems should be 0 2 m s 6 86 Variable speed fans with differential pressure control may be the most suitable solution for maintaining consistent performance and energy saving see also paragraphs 4 26 4 42 6 87 Some UCV systems are
124. ntilation system is not merely tempering the air but also providing the heating and or cooling requirements the following additional factors will need to be considered a internal or peripheral location b orientation of windows c variation in internal loads d level of control required Methods of control 2 48 The method of control selected for a ventilation system is governed to a large extent by the complexity of the system installed The options available range from an electrical spur to a building management system BMS 2 49 For single zone plant in staff areas local control with a run on timer if required is recommended as this can be turned off when the space is not in use thus saving both thermal and electrical energy Most supply and extract systems conversely are required to operate continuously while the department is in use thus some form of time control is necessary 2 50 For most ventilation applications in healthcare buildings the supply system is only required to temper the air hence the supply temperature of the plant can either be maintained at a constant level or controlled by a room sensor in an internal zone or return air duct if applicable 2 51 The control of individual plant items is covered in Chapter 4 with examples of typical control strategies in Chapter 5 For control of particular specialist ventilation and air conditioning systems refer to Chapter 6 of this document Specific requ
125. o allow for supporting mechanisms 6 103 New designs of operating luminaire should comply with the The traditional means of light support photometric requirements detailed in relevant sections of BS4533 and be is a central column rigidly fixed to the mounted such that there is a clearance of 1 m between the underside of the building structure Separate supports luminaire and the operating table top displaced from the centre of the clean zone would lead to improved air flow but as yet no manufacturer has Hood extract systems adopted this solution Special requirements 6 104 Extract canopies will be required over steam and heat emitting appliances for example sterilizers catering and washing equipment and for the extraction of toxic fumes over benches used for mixing sifting and blending procedures 6 105 Perimeter drain gulleys and corrosion proof grease eliminators should be provided on kitchen hoods Typical arrangements 6 106 The air flow rate must be sufficient to ensure an adequate capture velocity in the vicinity of the process typical values are as follows a evaporation of steam and like vapours 0 25 m s to 0 5 m s b chemical and solvent releases 1 0 m s C vapour or gases 5 m s to 6 m s d light dusts 7 m s to 10 0 m s Excessive velocities will be wasteful of power and generate noise 6 107 The lowest edge of the canopy should be 2 m above finished floor level with a minimum of 300 mm overhang beyond the edge of
126. o install and because of their greater input power requirements are increasingly more expensive to run 3 98 For normal applications in healthcare buildings low velocity systems are recommended and the use of higher velocities than those recommended is not likely to be economical Future trends are likely to be towards even lower optimum duct velocities however velocities lower than 2 5 m s are unlikely to be justified 3 99 The site will often dictate the main routing of ductwork systems but in general the design should seek to make the layout as symmetrical as possible that is the pressure loss in each branch should be as nearly equal as possible This will aid regulation and may reduce the number and variety of duct fittings that are needed Ductwork materials and construction 3 100 The choice of material to be used for the formation of a duct should take account of the nature of the air or gas being conveyed through the duct the environment in which the duct will be placed and the cost of the installation 3 101 Galvanised sheet steel is generally suitable and most economical for normal ventilating and air conditioning applications 3 102 In instances where moisture levels and or corrosive elements in the air being conveyed are very high aluminium stainless steel PVC or GRP ducts should be used Stainless or black steel are however the only suitable materials for high temperature ductwork 3 103 Where builders work duct
127. oms with still air that is the air velocity in the occupied zone is 0 1 m S when the resultant temperature is between 19 and 23 C and that levels of dissatisfaction do not increase when the temperature varies by within 1 5 K of the selected value 3 11 It has also been found that there is a relationship between preferred indoor temperatures and mean outside temperature Figure A1 2 in the CIBSE Guide indicates this relationship 3 12 The design conditions selected within patient areas must strike a balance between the comfort requirements of staff and patients who often have very different levels of clothing and activity In areas such as operating departments the comfort of the surgeon is of prime importance whereas in ward areas the patient requirements are the overriding factor 3 13 The effect of relative humidity on thermal comfort is less well defined than that of temperature For most applications the comfort range is between 4096 and 7096 in order to minimise the build up of static electricity and allow for evaporation of perspiration 3 14 Recommendations for the resultant temperatures and humidities of individual spaces are shown on activity data A Sheets but generally acceptable figures are given in Table 3 2 HTM 2025 DC reprinted with amendments January 1999 3 0 Assessment of service requirements Table 3 2 Internal conditions for design of plant Inside design conditions Season A Control
128. on a selected subject If you do not already use this free service or think you are not using it to its full capacity why not contact us and discuss your requirements You can contact us at The Stationery Office Standing Order Department PO Box 276 London SW8 5DT Tel 0171 873 8466 fax 0171 873 8222 We look forward to hearing from you HTM 2025 DC reprinted with amendments January 1999 About this publication Health Technical Memorandum HTM 2025 gives comprehensive advice and guidance on the operation of ventilation in all types of healthcare premises It is applicable to new and existing sites and is for use at various stages during the inception design upgrading refurbishment extension and maintenance of a building HTM 2025 focuses on the a legal and mandatory requirements b design of systems c maintenance of systems d operation of systems It is published as four separate volumes each addressing a specialist discipline a Management policy considers the overall responsibility of managers of healthcare premises It outlines legal obligations and clinical needs with respect to ventilation summarises the technical aspects and concludes with guidance on the management of systems b this volume Design considerations does not set HTM 2025 DC reprinted with amendments January 1999 out to give detailed instruction in design but highlights the overall requirements and considera
129. onal temperature control makes prediction of energy consumption very complex It is imperative that these calculations are performed to ensure optimum energy efficiency 3 60 Computer modelling is the preferred method however a manual method is available for example load and plant operation charts 3 61 The concept of load and plant operation charts is outlined in CIBSE guide section B3 The method requires the designer to establish the minimum and maximum loads on all zones across the range of external temperatures between winter and summer design conditions Once the load chart is complete the plant chart converts the loads to supply temperatures which are then superimposed on external air temperatures 3 62 Humidity levels are plotted based on a mean condition line of dew point temperatures and the required supply dew point temperature 3 63 When all temperatures for all zones are plotted on the plant operation chart set points and resetting schedules can be established From this information the outputs of individual heaters coolers and humidifiers can be established at any given external temperature When those loads are computed against annual frequency of occurrence of external temperatures as given in CIBSE Table A2 8 the annual energy consumption of individual elements and thus the air conditioning system can be established Assessment of condensation risk 3 64 Condensation of water vapour occurs whenever a surface temp
130. onditions 3 15 Minimum fresh air requirements 3 18 Limiting supply air conditions 3 21 Air purity 3 22 Humidity control requirements 4 55 3 26 Maximum noise levels Calculation of building loads 3 35 Air infiltration 3 39 Summertime temperatures 3 42 Peak heating load 3 46 Peak cooling load HTM 2025 DC reprinted with amendments January 1999 3 54 Annual energy consumption 3 64 Assessment of condensation risk Calculation of plant requirements 3 70 Air supply volumes 3 72 Plant sizing 3 80 Plantroom size and location 3 84 Provision of primary services 3 88 Discharge and inlet sizing and location 3 95 Heat rejection devices Air distribution arrangements 3 97 Ductwork distribution systems 3 100 Ductwork materials and construction 3 109 Duct sections 3 119 Standard ductwork fittings 3 128 Noise generation within the ductwork 3 132 Volume control damper locations 3 135 Fire damper types and locations 3 137 Access door locations 3 140 Diffuser and grille selection and sizing 3 152 Transfer grilles size and location 3 156 Pressure relief damper size and location 3 159 Thermal insulation Plant equipment selection page 33 General requirements 4 1 Air handling unit construction 4 8 AHU drainage system 4 14 Layout of plants 4 17 Provision of dampers 4 21 Health and safety aspects 4 24 X Vibration 4 25 Sequence of components Fans 4 26 General requirements 4 27 Acceptable types 4 29 Selection 4 33
131. onsideration should be given to the proposed methods for the regular cleansing of the humidifier s and their components 4 77 Ultrasonic humidifiers are available The action of ultrasonic frequencies should not be considered an effective method for control of micro organisms The supply of water to the humidifier should be free from viable bacteria The humidifier reservoir is accessible to micro organisms including legionellae carried by the incoming air and the water temperature in the humidifier during operation may be such as to encourage growth of these bacteria biofilms may form These units are capable of producing aerosols that may transmit legionellae Selection 4 78 A mains steam humidifier can be noisy and will be difficult to control if it is operated at an excessive steam pressure It should be sized for an operating pressure of approximately 1 bar and the pipework supplying it should be provided with a dirt pocket pressure reducing valve and steam trap installed as close as practicable to the humidifier so that the steam condition at entry is as dry as possible A temperature switch on the condensate line or equivalent design provision by the humidifier manufacturer should be incorporated to prevent spitting on start up 4 79 Most operational problems with mains steam humidifiers arise because of back pressure in the condensate discharge line Unless the condensate from HTM 2025 DC reprinted with amendments January 1
132. ontrol schemes 6 23 A Air distribution within rooms 6 26 Automatic control 6 34 Plant arrangement 6 36 X Ventilation of ancillary areas 6 44 Sterilizing and disinfecting unit 6 45 Reception 6 46 Recovery 6 48 Ultra clean ventilation systems 6 48 Special requirements 6 51 Design considerations 6 60 Operating department design 6 104 6 112 6 116 6 137 6 158 7 0 BA 7 3 7 8 consideration 6 63 Selection of UCV system 6 69 Performance of UCV system 6 70 Choice of system 6 75 Design requirements Hood extract systems 6 104 Special requirements 6 106 Typical arrangements 6 111 Control of hood extracts Bench extract systems 6 112 Special requirements 6 113 Typical arrangements 6 114 Control of bench extract systems Safety cabinet and fume cupboard extract systems 6 116 Special requirements 6 117 Arrangements for safety cabinet installations 6 123 Laminar flow cabinets 6 126 Arrangements for fume cupboard installations 6 134 Control of extract systems Plantroom ventilation 6 137 General requirements 6 141 Assessment of ventilation levels 6 148 Choice of ventilation system Ventilation of hydrotherapy suites 6 158 Special requirements 6 159 Arrangements for hydrotherapy pool installations 6 163 Control of hydrotherapy pool installations Commissioning page 89 General Location of dampers and test holes Information to be provided Appendix 1 Design of air movement control schemes for operating suites
133. or horizontal flow systems the use of partial or full walls the choice of special operating room etc are not discussed in depth Systems designed and commissioned in accordance with this guidance can provide a significant benefit to patients Design considerations 6 51 The design philosophy of a conventionally ventilated operating suite is based on the need to dilute contaminants and control both the condition and movement of air in the suite 6 52 The general objective of an ultra clean ventilation UCV system is to provide clean filtered air in the zone in which the operation is to be performed and sterile instruments and drapes are exposed This is achieved HTM 2025 DC reprinted with amendments January 1999 71 6 0 Special ventilation systems by means of a uni directional discharge of air from an air filter bank or diffuser over the sterile field of the operation Generally vertical flow systems provide a more effective solution than horizontal flow systems 6 53 Some factors which are important when designing operating departments with conventional ventilation systems are not relevant when a UCV system is to be installed UCV systems are so efficient in preventing airborne bacteria reaching the sterile zone and in reducing the bacterial concentrations in the remainder of the operating room that there is no need for complex air movement control schemes and except for the preparation room there is no need for high air supply volum
134. orporated to the drain outlet position The tray must be easily removable for inspection and maintenance 4 10 The trap need not be directly under the drainage tray provided that the pipework connecting the two has a continuous fall Each trap should be of the clear borosilicate glass type to show visibly the integrity of the water seal and should be provided with a means for filling A permanent marker on each trap should be provided to indicate the water seal level when the system fan is running at its design duty Each installation should incorporate quick release couplings to facilitate removal of the traps for cleaning HTM 2025 DC reprinted with amendments January 1999 33 4 0 Plant equipment selection 4 11 Traps fitted to plant located outside or in unheated plantrooms may need to be trace heated in winter The trace heating must not raise the temperature of water heated in the trap above 5 C 4 12 Pipework from each trap outlet should be thermoplastic copper or stainless steel tube Stainless steel could be particularly useful in situations requiring mechanical strength glass is not necessary The pipework should be a minimum diameter of 22 mm and have a minimum fall of 1 in 60 in the direction of flow and be well supported 4 13 Water from each trap must discharge via a type A air gap as specified in BS6281 Part 1 above the unrestricted spill over level of either an open tundish connected to a drainage stack via a second
135. ors should be referred to HTM 2025 DC reprinted with amendments January 1999 19 3 0 Assessment of service requirements 3 38 When calculating thermal loads due to infiltration based on Table A4 12 the following should be noted a infiltration allowances may be halved during unoccupied periods b where the majority of rooms have only single sided ventilation the load on the central plant will be roughly half the total of individual room loads c if the ratio of openable doors and windows exceeds 2596 on one wall only the tabulated infiltration rate should be increased by 2596 d if the ratio of openable doors and windows exceeds 2596 on two or more walls the tabulated infiltration rate should be increased by 5096 e on severely exposed sites the tabulated infiltration rates should be increased by 5096 f on sheltered sites the tabulated infiltration rates should be reduced by 33 g in rooms with mechanical supply systems half the tabulated value should be used for calculations of room loads to ensure that room temperatures can be maintained when the ventilation system is not operating Summertime temperatures 3 39 Summertime temperature calculations should be carried out for all rooms where the possibility of local solar or other heat gains may cause the temperature within an uncooled area to rise to an unacceptable level for the equipment and or procedures to be carried out 3 40 The calculation method for
136. ositioned to minimise the discomfort to occupants they should be unlikely to be blocked closed deliberately except in the case of fire shutters if required or rendered inoperative by prevailing winds 6 139 Plantroom ventilation air should not be used for any other purposes such as make up air for extract and where the plantroom contains combustion equipment the appliance pressure must not fall below the outside air pressure 6 140 Statutory regulations for plantroom ventilation are contained in the Building Regulations and further guidance in section B13 of the CIBSE guide Assessment of ventilation levels 6 141 Ventilation requirements must take into account all heat sources within a plantroom and where there are large glazing areas solar gains The ventilation rate should limit the maximum temperature within the plantroom to 32 C 6 142 As the level of equipment operating during mid season and summer is often lower than the winter condition and the cooling effect of the outside air is reduced it is necessary to calculate the minimum volume for each season of operation and the inlet and outlet grilles or fan sizes should be chosen to cater for the largest seasonal air volume 6 143 Replacement air should not be drawn through pipe trenches or fuel service ducts Where metal ducts penetrate walls and floors effective sealing should be provided to confine the ventilation to the boiler room and to meet fire protection requirement
137. pe and can be a vertical flow comprising a recirculating air module containing final filter and terminal HTM 2025 DC reprinted with amendments January 1999 73 6 0 Special ventilation systems Return air filters and fans may be incorporated into a false ceiling to improve headroom These do not include primary fresh air conditioning equipment within the module The module must be connected to the primary air conditioning system see Figures 6 3 and 6 4 b horizontal or cross flow comprising a recirculating air module standing vertically to produce a horizontal flow of air and containing final filter diffuser return air filters and fans PRIMARY A C SECTION TO OTHER ROOM IN SUITE RECIRCULATING AIR MODULE FINAL FILTER DIFFUSER PARTIAL FIXED WALLS petam min e DEMOUNTABLE i CLEARANCE WALLS SEE NOTE OPERATING TABLE 2 9 m FIXED earners S SEE NOTE Figure 6 3 Typical commercial modular system Note Make up air volume escapes to peripheral area via doors etc The system must have side walls which may fold to facilitate cleaning of the theatre A deflector at the top of the filter diffuser will be acceptable as an alternative to a full roof Regardless of which of the above systems is preferred the recirculation fan power may necessitate the inclusion of supplementary cooling coils within the module These s
138. perating suites Single flow 1 6 Thisis a room with only one door and a nett surplus of supply or extract air Parallel multi flow 1 7 Thisis a room with two or more doors through each of which the air flows either outwards high pressure or inwards low pressure for example lay up plan 1b Parallel series multi flow 18 Thisis a room having a nett surplus of supply or extract and with two or more doors One or more doors will be to an area of equal cleanliness and need not be protected hence the flow may vary between inwards and outwards the remaining door being to an area of greater or lesser cleanliness for example a sterile pack store plan 1a Series multi flow unbalanced 1 9 Thisis a room having a nett surplus of supply or extract and with two or more doors Air flows inwards through one or more doors and outwards through one or more doors Series multi flow balanced 1 10 This is a room as in paragraph 1 9 above but having either no mechanical ventilation or no nett surplus of supply or extract for example an anaesthetic room Bay 1 11 A room which has a permanent opening to the operating room may be considered as a bay off the latter for example a scrub Two categories exist a open bay the opening is larger than a normal single door opening The bay may be considered as part of the main room b semi open bay the opening is no larger than a normal single door opening In this case it is pos
139. r Worksheet WS 6 b Reference Te c Find summer supply temperature tiw 20 0 828 H O R C oom 1 Note The temperature of a space may be calculated from rae EO Gt tn On 0 828H Where t is temperature of source 1 C Q is flow from source 1 when all doors are closed m s H is heat gain in space kW Supply Flows inwards Heat Room gain kW H Q t Temperature C T Check doors to sterile areas Calculated T Maximum Door between room AT AT Remarks C permitted eat ot ole JL 104 HTM 2025 DC reprinted with amendments January 1999 Appendix 1 Design of air movement control schemes for operating suites Transfer grilles pressure relief dampers and pressure stabilizers Worksheet WS7 Reference Transfer grilles see clause B 5 NIS ae SNR e TOROS imt Pressure Flow Free Resultant No Location difference rate area Model p Remarks Pa m s m Pa eroe ES i cete pneu 4 iconem aa ee eee i ML RTA EG andi at ave b cei ene SEMINE sa RR am Pressure relief dampers see clause B 6 Pressure No Location difference Remarks Pa ele dies js uec TERN Pressure stabilizers see clause B 7 Note Where a stabilizer is acting both as series room door prot
140. r grille from the area of equal cleanliness 1 19 Conversely where the nominal pressure equals that of the lower pressure adjacent room extract ventilation and a transfer grille to the lower pressure adjacent room should be provided for example the disposal room in Plan 5a Series multi flow unbalanced 1 20 These rooms are somewhat similar to those in paragraph 1 15 above but because the pressure lies between that of the rooms on either side the back flow problem does not exist 1 21 Where the room has a nett surplus of mechanical supply air a transfer grille should be located in or adjacent to the door through which air flows outwards and the mechanical supply flow rate to the room should be chosen to give protection when this door is open Series multi flow unbalanced 1 22 Where the room has a nett surplus of mechanical extract air a transfer grille should be located adjacent to the door through which the air flows inwards and the mechanical extract flow rate to the room should be chosen to give protection when this door is open 1 23 The grille must be sized for the protection requirement of the opposing door when open When the room on the high pressure side is depressurised there is a possibility of back flow through gaps around the door but this problem may be ignored Series multi flow balanced 1 24 In these rooms a transfer device is required adjacent to each doorway to provide a flow path for the air requi
141. range Dry bulb temp C 96 sat Winter heating 22 40 nominal 15 to 25 C 4 596 096 Summer cooling 20 60 nominal 15 to 25 C 096 596 Manual selection 15 to 25 C max 5096 sat minimum control range obtainable at for using flammable non extreme external anaesthetics conditions only 5 096 Minimum fresh air requirements 3 15 For most applications involving human occupancy the dilution of body odours is the critical factor in determining ventilation requirements and where natural ventilation or full fresh air systems are used all ventilation air will be fresh 3 16 Where odour dilution is the overriding factor it is recommended that 8 litres second person should be taken as the minimum ventilation rate however this rises to 32 litres second person for rooms with heavy smoking CIBSE Table B2 2 3 17 n non standard applications such as laboratories or operating departments the particular requirements for each area should be considered independently in order to determine the overriding minimum requirement for ventilation Limiting supply air conditions 3 18 Where the ventilation system is used to maintain conditions within the space or pressure differentials between spaces this requirement may exceed that for provision of fresh air In these instances recirculation systems can be used if appropriate in order to reduce the energy consumption of the system 3 19 For most applications in healthcare buil
142. re prone to inaccuracy and drift 4 64 Off coil control is however expensive to operate in terms of energy consumption due to the fact that there is no feedback of room loads and thus at low loads and in systems where there are large zonal variations significant over cooling and reheating will occur 4 65 On systems with two speed operating it is usual to isolate the cooling coil upon selection of low speed In addition on system shutdown low air flow or fan failure the cooling coil must be isolated Humidifiers General requirements 4 66 The most important requirement for a humidifier is to create complete mixing of the steam with the air and the manufacturers instructions should be followed regarding minimum distances which should be allowed before bends or other components 4 67 The number and length of steam injection manifolds to be used is dependent on various factors such as duct cross section area air velocity air dry bulb temperature and manifold design 4 68 Adequately sized glazed access doors and low voltage swimming pool type weatherproof bulkhead light fittings are essential for maintenance purposes The light fittings should be mounted so that their bulbs can be changed from outside the duct 40 HTM 2025 DC reprinted with amendments January 1999 4 0 Plant equipment selection 4 69 All parts of the humidifier and its associated ductwork in contact with moisture must be manufactured from corrosion resistant
143. re systems having a relatively low proportion of fittings 3 115 Flat oval ducting provides an alternative to circular ducting principally where there is a limitation on one of the dimensions in the space available for the duct run 3 116 Other sections may be used such as triangular sections to pass through roof trusses Such sections present difficulties in the provision of HTM 2025 DC reprinted with amendments January 1999 27 3 0 Assessment of service requirements fittings and connections to standard plant items and are likely to be more expensive than traditional sections 3 117 Builder s work ducts and intake chambers should be surface treated and sealed to prevent dust particles being picked up by the airstream 3 118 Flexible ductwork can be used for final connections to grilles and diffusers provided it is constructed to meet the fire precautions recommended in CP413 that is the length of flexible ductwork branches is not greater than 3 7 metres and does not pass through fire compartment walls floors or enclosures of sub compartment walls or enclosures or through cavity barriers Standard ductwork fittings 3 119 All fittings should conform to DW142 Wherever possible long radius bends large radius main branches not more than 45 angle sub branches and long taper transformations should be used 3 120 Fittings should be arranged with vanes in sub branches connected directly to grilles and diffusers and turning va
144. reas within healthcare buildings and due to the capital and running cost implications its inclusion should be kept to a minimum 2 16 Areas whose functions do warrant the installation of full air conditioning include operating departments intensive therapy units manufacturing pharmacies and areas with sensitive equipment where the environment needs to be maintained within specified limits to prevent equipment failure Specialist ventilation 2 17 Due to the nature and extent of activities carried out in healthcare buildings there are needs for a wide range of specialist ventilation systems These types of system which are generally required in individual departments and typical arrangement are given in Chapter 6 2 18 The activities within some departments will require the provision of local exhaust ventilation LEV This is a statutory requirement under COSHH wherever the escape of chemicals toxic fumes biological material or quantities of dust into the general area would present a hazard to the occupants Air scrubbing 2 19 Air scrubbing is the process by which air is recirculated through a filter in order to maintain airborne contamination at an acceptable level An example of this is laminar flow cabinets Ventilation for general areas 2 20 Table 2 1 provides recommended air change rates temperatures and pressures for general areas which require mechanical ventilation in healthcare buildings 8 HTM 2025 DC reprinted wi
145. red Split comfort air conditioners 2 37 Split comfort air conditioners room conditioning or cassette units are used increasingly where there is a small local requirement for cooling for operational purposes 2 38 Until recently the application of these units was restricted to single rooms but recent technological advances have led to the development of systems which allow multiple indoor units to independently provide either heating or cooling served by a single outdoor unit These systems enable good temperature control of a number of rooms with maximum energy efficiency HTM 2025 DC reprinted with amendments January 1999 11 2 0 Provision of ventilation in healthcare buildings 2 39 Split comfort air conditioners can often provide an effective economic solution to cooling needs where a central refrigeration system is not practicable 2 40 Whether single or multiple systems are used it is essential that the designer gives due consideration to the provision of maintenance the source of electrical supply and the environmental effects to the refrigerant used Dilution ventilation 2 41 Dilution ventilation may be appropriate under COSHH in certain circumstances provided that the threshold limit values TLV are capable of being maintained without excessive air change rates In addition the source and distribution of the contaminants within the space must be reasonably uniformed In cases where substances are highly toxic or where t
146. red to protect the opposing door when opened Series multi flow balanced 1 25 These transfer devices will normally be pressure stabilisers although transfer grilles may be used where a large amount of excess air is to be exhausted from the operating room when all doors are closed for example anaesthetic rooms HTM 2025 DC reprinted with amendments January 1999 107 Appendix 1 Design of air movement control schemes for operating suites 1 26 The calculation procedure is to assume that pressure stabilisers are used and then if there is sufficient excess air change to transfer grilles as described in paragraphs 1 43 to 1 44 Bay 1 27 a Open bay a bay of the open type for example scrub up is considered to be part of the operating room and provided air movement is satisfactory no specific extract is required Bay semi open Note the pressure stabiliser may be replaced by mechanical Bay open extract b Semi open bay in a bay of the semi open type protection of one area from the other is possible for example scrub up As stated in paragraph 6 2 the need for protection between operating room and scrub room is not very great Better use of air can therefore be achieved in this case by installing a pressure stabiliser between the scrub room and clean corridor This will allow a flow of air through the scrub room at all times except when a door is opened elsewhere in the suite The pressure stabiliser will th
147. rlocked so that the supply fan does not operate until flow is established within the extract system 6 164 Time clock control should be provided with a local override switch to extend the normal operating period as required 6 165 Night set back temperature in the range of 21 25 C and high humidity control in the range of 60 75 sat should be provided to override the time clock in order to prevent condensation The exact set points should be ascertained post installation 6 166 A remote indication panel should be provided in the pool hall giving a visual display of the pool water and pool air temperature 88 HTM 2025 DC reprinted with amendments January 1999 7 0 Commissioning General 7 14 Commissioning is an essential process for ductwork systems and if the needs of on site regulation are not foreseen and provided for in the design stage balancing the system within accepted limits may never be possible Procedures for commissioning air handling systems are given in CIBSE Commissioning Code A and in BSRIA Application Guide 1 75 The Validation and verification volume of this HTM sets out commissioning procedures 7 2 The duct sizing procedure should take into account the requirements of system balancing and the position and number of regulating dampers included in the design should be sufficient for this purpose Location of dampers and test holes 7 3 Balancing commissioning dampers will be required in each branch of
148. rti os cites Transfer grille irc Pressure relief damper les HTM 2025 DC reprinted with amendments January 1999 97 Appendix 1 Design of air movement control schemes for operating suites Air Movement Control Worksheet WS 2d Peripheral room cccccsccsccsssecesccesesevees type Reference series multi flow balanced Nominal pressure Pa Note In this type of room the supply and extract air flow rates are equal and take no part in the air movement control AMC Firstly open door to higher pressure area Room pressure then becomes 25 or 17 or Pa See table 6 2 Air flow m s Remarks Flow required through open doorway to give protection See table 6 2 At above pressures leaks through closed doors are Structural leakage Next open door to lower pressure a Room pressure then becomes Out in Remarks Flow required through open doorway to give protection At above pressures leaks through closed doors are Pa AP Structural leakage Total Q2 Zour Zin ues ve outwards Flow through transfer device TD1 to Lower protect door 1 Q4 at resultant pressure TD1 T A 7 Door 2 Flow through transfer device TD2 to protect door 2 Q2 at resultant AP aauina Higher pressure 7 TD2 98 HTM 2025 DC reprinted with amendments January 1999 Appendix 1 Design of air moveme
149. s 3 23 The comfort band for humidity is wide current practice recommends that it should be kept between 40 and 60 saturation 3 24 Below 40 saturation there is a tendency to feel dryness in the eyes nose and throat while static electricity increases and organisms spore making them more difficult to kill by means of surface disinfectants 3 25 At humidity levels above 70 there is increased risk of surface condensation and mould growth and organisms are more likely to multiply Maximum noise levels 3 26 Noise will be generated in an air distribution system by the fan ductwork fittings dampers and grilles Again the specified maximum noise level will depend on the activities within the occupied spaces 3 27 The overall noise level should be to levels set down in Hospital Design Note 4 Noise control amended by Health Notice HN 76 126 although general requirements are given in Table 3 3 3 28 Attenuation should be incorporated into the ductwork system or plant arrangement as necessary to reduce noise from fans and plant items in order to achieve the acceptable limits within the rooms at the design air flows 3 29 Plant noise should not be greater than 85 dBA within the plantroom from the fans coolers heaters humidifiers etc when starting up or running and should be reduced to lower noise levels where the plant is near to departments sensitive to noise 3 30 Attention must be given to the reduction of tonal compo
150. s Plan 1a single corridor with sterile pack store 6 20 1b single corridor with lay up 2a linked corridor with sterile pack store 2b linked corridor with lay up 3 linked corridor with external scrub and sterile pack store 4 Nucleus plan two corridors with sterile pack store and disposal hatch 5a two corridor with sterile pack store 5b two corridor with lay up These appear in diagrammatic form in Figure 6 1 which shows the relationships of rooms and the various doors and transfer devices between them and should not be regarded as architectural layouts The schemes have been developed using the calculation procedure described in Appendix 1 of this HTM Important features of the solutions are a HTM 2025 DC reprinted with amendments January 1999 zonal trimmer heaters a trimmer heater battery is advocated when calculations indicate that the temperature differential between rooms may be greater than 2 K Generally this will only be the case in the preparation room the preparation room sterile pack store operating room interface these rooms are deemed to be of equal cleanliness and thus a transfer grille is required between these rooms preparation lay up disposal room interface pressure relief dampers are recommended here to provide an airpath when doors are closed while preventing back flow when a door is opened elsewhere operating room anaesthetic room interfa
151. s 1993 1994 Medical gas pipeline systems 1994 Supp 1 Dental compressed air and vacuum systems 1997 Supp 2 Piped medical gases in ambulance vehicles 1997 2023 Access and accommodation for engineering services 1995 2024 Lifts 1995 26 Commissioning of oil gas and dual fired boilers with notes on design operation and maintenancet Hot and cold water supply storage and mains services 1995 28 to 29 2030 Washer disinfectors 1995 32 39 2040 The control of legionellae in healthcare premises a code of practice 1993 41 to 44 2045 Acoustics 1996 46 49 2050 Risk management in the NHS estate 1994 51 54 2055 Telecommunications telephone exchanges 1994 2021 2022 2027 116 2065 Healthcare waste management segregation of waste streams in clinical areas in preparation 2066 Supply and treatment of water in preparation 2070 Estates emergency and contingency planning in preparation 2075 Clinical waste disposal treatment technologies alternatives to incineration 1998 Component Data Base HTMs 54 80 54 1 User manual 1993 55 Windows 1989 56 Partitions 1989 57 nternal glazing 1995 58 nternal doorsets 1989 59 ronmongeryt 60 Ceilings 1989 61 Flooring 1995 62 Demountable storage systems 1989 63 Fitted storage systems 1989 64 Sanitary assemblies 1989 65 Health signst 66 Cubicle curtain track 1989 67 Laboratory fitting out system 19
152. s Penetration of fire barrier walls by ventilation ducts should be avoided if possible 6 144 Fire dampers in ventilation ducts should be electrically interlocked with the boiler plant 6 145 Care must be taken to prevent any noise generated in the boiler room emerging from natural or mechanical ventilation openings to the detriment of the surrounding environment Particular care is necessary with mechanical flue draughts and fan diluted flue systems 6 146 Information on required air volumes is contained in section B13 of the CIBSE guide 86 HTM 2025 DC reprinted with amendments January 1999 6 0 Special ventilation systems 6 147 Where combustion plant is installed the high level outlet openings should be sized to cater for the total ventilating air quantity and the low level supply openings sized to cater for the total combined ventilating and combustion air quantity Choice of ventilation system 6 148 The ventilation air may be introduced and exhausted by either natural or mechanical means or a combination of both however where possible natural systems are preferred 6 149 Generally small installations at or above ground level should have their combustion and ventilation air provided by natural means employing both high and low level openings 6 150 Basement internal and large installations at or above ground level will usually require a combination of natural and mechanical ventilation If the air flow route is
153. s are more usually controlled by a minimum humidity sensor located in the supply duct s following the last heater battery 4 86 Overriding controls separate from the normal plant humidistat should be installed Their purpose is to prevent excessive condensation when starting up A time delay should be incoporated into the humidifier control system such that the humidifier does not start until 30 minutes after the ventilation plant start up In addition a high limit humidistat should be installed to switch off the humidifier when the saturation reaches 70 This humidistat is to control added moisture it is not necessary to install a de humidifier to reduce the humidity of the incoming air if it already exceeds 7096 The normal humidifier control system should ensure that the humidifier is switched off when the fan is not running Filtration General requirements 4 87 The purpose of filtration is to reduce the level of airborne contamination entering a building and is generally carried out in one or two stages 4 88 General ventilation supply plant should incorporate air filters of grade EU3 sized for a maximum face velocity of 2 5 m s Coarse pre filters may be justified where the intake air is exceptionally polluted Extract filtration will only be required where heat recovery devices are installed or contaminated air is required to be filtered prior to discharge to atmosphere 4 89 In urban or other areas of high atmospheric pollution
154. s are used these may be constructed of various materials however brickwork ducts must be rendered and a greater allowance made for leakage 3 104 Galvanised black and stainless steel ductwork should be manufactured and installed to DW 142 HVCA specification for sheet metal ductwork but excluding the use of bolt through supports 3 105 GRP and PVC ductwork should be manufactured and installed to DW 151 HVCA specification for plastic ductwork 26 HTM 2025 DC reprinted with amendments January 1999 3 0 Assessment of service requirements 3 106 The inside of the ductwork should be free from structural projections and as smooth as possible Flanged gasketed joints are preferred 3 107 Ductwork must be fire stopped where it penetrates fire compartment walls floors and enclosures cavity barriers and sub compartment walls or enclosures and provided with weatherproof collars where roofs or external walls are penetrated 3 108 In inherently wet areas such as the base of fresh air inlet ducts the ductwork may require draining to avoid any formation of water with the layout of any drains as specified for paragraphs 4 8 to 4 13 Duct sections 3 109 Ducting is generally available in rectangular circular and flat oval sections although other sections may be made for special situations 3 110 Rectangular ducting is most common on low pressure systems for the following reasons a it can readily be adapted to fit into the spa
155. sible to protect the bay from the main room by provision of air supply or extract in the bay or by passing air to or from another area HTM 2025 DC reprinted with amendments January 1999 93 Appendix 1 Design of air movement control schemes for operating suites Worksheet WS 1 Reference Calculation Sheet for Flow rates Room Name 1 Summer temperature control Heat gain 2 Acceptable At 3 Air flow rate Sc 4 Winter temperature control Heat loss 5 Acceptable At 6 Air flow rate SL _ Loss Atx 1 2 7 Dilution of bacterial contaminants Air flow rate Sp or Ep 8 Maximum of Sc SL Sp or Ep 9 Air movement control Air flow rate for air movement control Samc or Eamc From WS2 WS3 or WS4 10 Final supply flow rate Sc 11 Final extract 12 Total supply 13 Total extract 94 HTM 2025 DC reprinted with amendments January 1999 Appendix 1 Design of air movement control schemes for operating suites Air Movement Control Peripheral room type single flow Worksheet WS 2a Reference Nominal pressure Consider door to soose open Air flow m s In Remarks Flow required through doorway to give protection Structural leakage or two Zm Zour _ Transf
156. stems are less effective and are not the preferred solution There may be occasions however where architectural engineering economic or workload considerations prevent the installation of vertical flow systems and only a horizontal flow system can be installed 6 73 In the horizontal flow systems personnel working between the filter and surgical wound will disperse bacteria which is more likely to enter the wound This may be minimised by the use of improved clothing and operating procedure to reduce dispersion of bacteria 6 74 The use of lines on the floor delineating the extent of the clean zone in all systems and the no entry zone in horizontal systems will assist staff and are therefore recommended see Figures 6 4 and 6 5 ZONE FOR SURGICAL SERVICES COMPRESSED AIR VACUUM AND SOCKET OUTLETS CLEAN ZONE ZONE FOR ANAESTHETIC SERVICES MEDICAL GAS AND ELECTRICAL SOCKET OUTLETS Figure 6 5 Plan of vertical flow supply 76 HTM 2025 DC reprinted with amendments January 1999 6 0 Special ventilation systems Design requirements General 6 75 Vertical flow systems are preferred they should have a minimum area of 2 8 m x 2 8 m This is the area projected on a plan of the supply air terminal within the partial or full walls with a clearance to the underside of the fixed partial wall of 2 m from finished floor level FFL Any air outside this zone should not be considered as ultra clean although the level of microbio
157. systems Table 6 6 a Air movement control specification for standard plans supply and extract flow rates Item Specification Plan Room Nominal Flow pressure rate 1a 1b 2a 2b 3 5a 5b Pa m3 s 0 75S S Operating room 25 0 65 S y i OR 0 80 S 0 76 S Air Anaesthetic 14 Ost bs c De sou ox A UY Supply S room AN Q 15 E KC E de and Sterile pack 2545 0 10S Extract E store SPS flow rates Instrument 35 0 34 S and lay up LU nominal Scrub bay SC 25 04010 es a SX l9 T o room 0 00 E pressures Disposal DI 5 OATE E coo s o 0x5 0 10E du Clean corridor 3 d ach 5 2 X seno EP M CC Outer corridor 0 ox DC Total supply to 1 00 m3 s the suite 1 14 i x 0 95 1 01 Notes S Supply E Extract Ac hr Air changes per hour 6 32 The theatre control panel should also include plant status indication temperature and humidity indicating gauges and means of adjusting the setpoint for temperature and humidity The panel should also include the air sampling terminal 6 33 The humidity within the operating department should be kept within the range 4096 to 6096 Provision should be made for raising the minimum level to 5096 in the unlikely event that flammable anaesthetics are to be used The humidifier should be selected to humidify to 50 saturation at 20 C during the design winter outside conditions and the cooling coil should be able to remove sufficient moisture so th
158. t causing discomfort to the occupants 6 156 Where it is impractical to provide sufficient natural ventilation to remove the heat emitted by the plant both mechanical supply and extract will be required 6 157 The high level extract should be sized to cater for the total ventilating air quantity and the low level supply should exceed the total combined combustion and ventilating air quantity by at least 2596 as above HTM 2025 DC reprinted with amendments January 1999 87 6 0 Special ventilation systems Ventilation of hydrotherapy suites Special requirements 6 158 The Departmental Cost Allowance for a hydrotherapy suite includes for heat recovery via a heat pump system Arrangements for hydrotherapy pool installations 6 159 The quantity of supply air should be calculated as 25 litres sec m wetted surface with the wetted surface taken as 11096 of the pool water surface area 6 160 A recirculation plant is recommended with a minimum of 2096 fresh air 6 161 As far as practicable recirculated pool air should be provided to the ancillary changing and recovery accommodation with the only extract from the toilets laundry utility room and pool hall 6 162 Supply air to the pool hall should be introduced at high level and directed towards the perimeter to mitigate condensation with extract air taken from directly over the pool Control of hydrotherapy pool installations 6 163 The supply and extract fans should be inte
159. t control schemes for operating suites General 1 1 The standard plans are given in paragraph 6 1 If these standard solutions cannot be used the following procedure should be adopted which will result in an acceptable design 1 2 The method is concerned with the calculation of air flow rates to ensure that correct air movement occurs between rooms when any one door is open Under most circumstances the air quantities required for air movement control will approximate to those for either temperature control or bacterial contaminant dilution and the air flow rate to the operating department will not exceed 1 m sec This flow rate is sufficient to control the effects of any slight reverse flows occurring when a door is opened 1 3 The progression through the design procedure is shown in the Air flow design procedure chart Figure Al and is supported by the worksheets WS1 to WS7 described below It is recommended that a plan of the suite and an air flow network be made to collate all information Flow rates air transfer devices etc are entered as required The remainder of this Appendix may be treated as reference data to assist in the various steps The following symbols are used a S supply air flow rate for summer temperature control b Sw supply air flow rate for winter temperature control c Sp supply air flow rate for dilution of bacterial contaminants d Ej extract air flow rate for dilution of bacterial contaminan
160. t recovery in a ventilation system 4 107 Where a local comparable heat demand can be supplied economically by thermal reclamation heat recovery equipment should be installed Where extracted air has a high moisture level the cooling effect on the extract air may require drains for condensate and access for cleaning heat exchangers Selection should be based on efficiency maintenance requirements and the practical reliability of the preferred system Run around coils offer ease of installation in either new or existing plantrooms and like plate heat exchangers require little maintenance 4 108 Where heat recovery devices are installed they should be protected on the extract air side by a grade EU2 filter to prevent clogging fitted in accordance with the requirements of paragraphs 4 87 4 101 This subject is covered in Energy Efficiency Heat recovery from ventilation Systems Location 4 109 Heat recovery devices should be installed with an upstream filter on the extract side and prior to the cooling coil or main heater battery on the supply side Control 4 110 It is essential to consider the control of both the heat recovery device and the fog frost coil when assessing the economics of heat recovery as all energy provided by the frost coil will directly reduce the heat exchange of the heat recovery device To this end the off coil setting of the frost coil should be the minimum possible to protect the primary filter around 2 C
161. t selection Selection 4 99 Some general guidance on the application of the various grades of filter is given in Table 4 2 Table 4 2 Filter applications Grade Application 2 3 Pre filters and filters for systems serving areas not requiring any great degree of cleanliness such as toilet supply systems and light industrial applications 4 For application as main filters where low to moderate cleanliness is required 5 Main filters for general applications where decor protection is not critical Suitable for paint spray installations 6 As 5 but with added decor protection Intermediate filter to extend life of a HEPA main filter 7 As 5 but for use where protection of decor is particularly important Typically operating room 8 High protection from dust staining suitable for computer room and other areas containing electronic equipment 9 For high quality filtration but where HEPA filters are not justified for example Class 3 clean room applications 4 100 In addition to the nine grades of filter already described there is another classification known as High Efficiency Particulate Air HEPA filters sometimes known as absolute filters They are designed to provide very high efficiency filtration of tiny particles in the sub micron size range 4 101 HEPA filters are expensive and their use should be kept to a minimum Where used HEPA filters should be of the replaceable panel type with air proof seals Are
162. t to be isolated when cleaning is in progress 4 20 A main volume control damper should be provided in the main plant to set the design flow rate during commissioning The damper must be capable of being locked in any position If it is intended to use it for plant isolation also it must be capable of being reset to give the design air flow without the need for re measurement Health and safety aspects 4 21 It is essential that the main plant ductwork is located far enough from the floor to permit the correct installation of drainage systems for cooling coils humidifiers and heat recovery systems Easy access for maintenance of drainage systems and their associated pipework must be provided 34 HTM 2025 DC reprinted with amendments January 1999 4 0 Plant equipment selection Fresh air intake NNNNNNNNNNNNNNS 4 Control damper NNSNSNNNNNNNNNSNSS Frost coil o I gt 28 33 e o 2 5 E Fan a Pre filter Silencer 5 YESEBmS 9999999 N 99999 99999949 9999995 Fans FRI Access light inspection window e9999 Wii Heat recovery coil e99999 A Cooling coil 4 o Cc 9g D 5 az o a oi ae S o Jg e o PH S l S 3 g Heating coil a A D 7 2 a mee Humidifier o 3 E a D e 4 E 3 w PIS Final filter Wood dad A Balancing damper jio bunean 2 Figure 4 1 Typical operating suite ventilation system
163. taff base 5 14 Where two speed controls are installed the set back facility for each plant should depress the control temperature to around 15 C exclude any humidification and cooling from the system and reduce the supply and extract air volumes by around 5096 Provided any desired direction of air movement from clean to less clean can be maintained it may be possible to turn the associated extract fan off during set back Methods of time switching Start up control 5 15 The plant start control should contain a control logic that will start the plant in the sequence set out in the algorithms in Tables 5 1 and 5 2 Set back control 5 16 If a two speed fan or twin supply fans are used the volume can be reduced to 5096 and the control temperature set point depressed to around 15 C when spaces are in the set back position 5 17 The chosen method will depend on the likely usage and economic advantages of the system Provision should be made to lock out the alarms when on set back and to interlock the extract fan humidifiers cooling coils main and trimmer heaters with the fan so that they cannot operate when the air system is off See also the control algorithms in Tables 5 3 and 5 4 5 18 The fire control panel should have restricted access for the fire officer and include independent on off control and indication of the supply and extract HTM 2025 DC reprinted with amendments January 1999 49 5 0 Automatic control Environ
164. ted from copper tubes with copper fins extended on the downstream side in the form of an eliminator and HTM 2025 DC reprinted with amendments January 1999 39 4 0 Plant equipment selection electro tinned after manufacture are preferred All parts of the coil and its associated ductwork in contact with moisture must be manufactured from corrosion resistant materials Stainless steel GRP or plastic finishes are preferred Location 4 60 Micro organisms which multiply in moisture cannot be avoided when the coil is dehumidifying but the risk of infection will be reduced by locating the final filter downstream of the coils 4 61 The standard arrangement of cooling coils in air handling units is given in Chapter 3 Control 4 62 There are two basic methods of control for cooling coils a off coil control used in multi zone systems or single zone systems where close humidity control is required to provide a constant maximum off plant condition which satisfies the temperature and high humidity requirements of the zone with the highest load b sequential control used in single zone systems or multi zone systems with averaging sensors where close control is not required A room or duct temperature sensor controls the cooling coil and heater battery in sequence to maintain constant room conditions 4 63 The advantage of off coil control is that accurate humidity control can be provided without relying on humidity sensors which a
165. th amendments January 1999 6661 enuer sjuawpuawe yum pajuldes DG SZOZ NLH ROOM TEMPERATURE C NOMINAL VENTILATION TYPES amp RATE ROOM DESCRIPTION SUMMER WINTER PRESSURE SUPPLY GENERAL FOUL IF COOLING WITH RESPECT AC h EXTRACT EXTRACT TO AC h AC h SURROUNDINGS ALL DEPARTMENTS WCs 18 C ve z 10 BATHROOM SHOWER 21 C ve 6 LABORATORIES Ambient 3 C 18 C ve TO SUIT ROOM LOADS B TREATMENT 25 C 21 C 0 10 10 STAFF CHANGE 21 C ve 3 B COFFEE LOUNGE is 8 C ve 3 E BEVERAGE ROOM 8 C ve 5 DIRTY UTILITY 8 C ve 10 CLEAN UTILITY 8 C ve 6 B Table 2 1 Typical internal design conditions Refer to Activity DataBase for specific details sBuipjing auesyyeay ui uone nuaA jo UOISIAO d O Z 2 0 Provision of ventilation in healthcare buildings Acceptable methods Use of natural ventilation 2 21 With the trend towards better sealed buildings infiltration through building leakage has significantly reduced and more attention is now given to the provision of purpose made ventilation openings to achieve the necessary flow rates 2 22 However internal partitions fire compartment walls and closed doorways can often impede the flow path and when this happens the process will be more dependent on single sided ventilation Nevertheless even with this degree of compartmentation acceptable ventilation may still be achieved without window openings which would prejudice safety securit
166. than corrective measures 4 125 Fans radiate noise through both the inlet and outlet connections and it may be necessary to provide attenuators to limit the noise from both of these connections 4 126 Attenuation or other sound absorbing material should not be applied to the inside surface of the duct system after the final filter owing to the risk of mechanical damage and the subsequent dispersal of the media into the ventilation system 4 127 In addition attenuators should be located so that insulation is not nearer to a fire damper than one metre and is not fitted anywhere after the final filter Requirements for particular applications 4 128 Rooms in operating departments typically have hard surfaces for hygienic reasons This makes the room acoustically very live that is the reverberation times will be long Due account must be taken of both the direct noise and the reverberant diffuse noise from any source in the room HTM 2025 DC reprinted with amendments January 1999 47 5 0 Automatic control General requirements Requirements for automatic control 5 1 The basic requirements for an automatic control system are as follows a facilities to start set back and stop the plant b temperature control and indication c humidity control and indication d alarms to indicate plant failure low air flow and filter state 5 2 The designer should consider whether it is necessary for the supply and extract fans to be int
167. the equipment on all sides 6 108 A compact arrangement of equipment but with access for maintenance will minimise the canopy area and hence reduce the air volume necessary to achieve the optimum capture velocity 6 109 Hoods required for the control of heat gain and vapours may be connected to the general extract system when it is convenient to do so but where non corrosive ductwork materials are necessary a separate discharge is preferred 6 110 Lighting and internal divider plates are often required to be built into the perimeter of large canopies however built in shelving systems are not recommended as they interfere with the airflow and constitute a maintenance problem 82 HTM 2025 DC reprinted with amendments January 1999 6 0 Special ventilation systems Control of hood extracts 6 111 Provided that it does not interfere with the operation of the department when not in use the ventilation system for the hood extract and any associated supply can be shut down To this end local control should be provided Bench extract systems Special requirements 6 112 Bench extract ventilation is required in departments such as pathology and mortuary where activities involve the release of malodorous or toxic fumes which should not be inhaled Typical arrangements 6 113 Each ventilated position will usually be accommodated in a continuous run of benching which should not be more than 650 mm from front to rear and which shou
168. thus their use is restricted to applications such as fan coil units Fan location and connection 4 33 Fans can be positioned to either blow through or draw through the central plant The main advantages of a blow through unit are alower supply air moisture content can be achieved e the cooling coil and humidifier drains will be under positive pressure 4 34 The consequent disadvantages of this arrangement are a there is greater risk of condensate leakage through the casing of the cooling coil b an additional plant section is required at fan discharge to reduce the velocity before the next plant component 4 35 The fan performance figures given by manufacturers in their catalogue data are based on tests carried out under ideal conditions which include long uniform ducts on the fan inlet outlet These standard test connections are unlikely to occur in practice the designer should therefore ensure as far as is practical that the fan performance will not be significantly de rated by the system This objective can be approached by ensuring that the fan inlet flow conditions comprise uniform axial flow velocities with low levels of turbulence 4 36 Where the outlet duct is larger than the fan discharge connection there should be a gradual transition with a following section of straight duct having a length equivalent to three duct diameters 4 37 The design of the fan inlet connection must be carefully considered to avoid s
169. ties in the occupied zone in summer 3 148 In order to ensure satisfactory air movement within a space it is necessary to consider interaction between air movement from adjacent terminals and ceiling mounted fixtures light fittings etc as well as interaction between air movement and room surfaces 3 149 If the supply and extract terminals are too close short circulating may occur while if they are too far apart stagnant zones may be formed Where two opposing air streams meet the individual velocities must not be greater than 0 25 m s 3 150 Supply and extract grilles and diffusers should be fitted with opposed blade dampers for fine balancing purposes 3 151 Further guidance on the selection of grilles and diffusers is given in Section B3 of the CIBSE guide Transfer grilles size and location 3 152 Transfer grilles are required in locations where there is a significant imbalance between the supply and extract rates in a room to relieve any pressure differentials which may affect the operation of the spaces and or the ventilation system Minor air flows can be catered for by leakage around doors and frequent opening 3 153 While air transfer grilles in walls partitions or doors etc are not strictly part of the ventilation system they form essential components of the building s air distribution 3 154 Care needs to be taken to ensure that the positioning of transfer grilles does not interfere with the fire or smoke integrity
170. tions that should be applied to the design up to the contract documentation c Validation and verification gives general advice for ensuring that the installed equipment has been formally tested and certified as to contract The importance of correctly setting to work and commissioning the completed installation is emphasised The handover procedure including the provision of documentation and training is set out Q Operational management provides information to those responsible for overseeing day to day operation and maintenance Safe systems of work record keeping and legal obligations are included Guidance in this Health Technical Memorandum is complemented by the library of National Health Service Model Engineering Specifications Users of the guidance are advised to refer to the relevant specifications About this publication The contents of this Health Technical This HTM was written with the advice Memorandum in terms of management and assistance of experts in the NHS policy operational policy and technical and industry guidance are endorsed by T TP References to legislation appearing in a the Welsh Office for the NHS in the main text of this guidance apply in Wales England and Wales Where references differ for Scotland and or Northern b the Health and Personal Social Ireland these are given in marginal Services Management Executive notes Where appropriate marginal in Northern Irela
171. tment should be mechanically ventilated and that the plant be sized to cope with all heat losses thereby making separate radiator or convector systems unnecessary The grilles and diffusers should be located to eliminate condensation on windows and provide even air distribution The use of ceiling heating and embedded heating panels is not recommended Ventilation requirements 6 37 Table 6 6 a gives guidance on the operating department areas in descending order of cleanliness and this should be considered in the overall design of the department ventilation systems The specified flow rates of air through doors given in Table 6 6 c for the operating suite are not necessary for other areas of the department however the airflow directions must be maintained from the clean to the less clean areas 6 38 All windows in the department should be double glazed and hermetically sealed in order to ensure that the desired air flow pattern is maintained under all external environmental conditions and to avoid infestation Systems design 6 39 The design of the ventilation system for the ancillary rooms depends on the overall configuration of the department The ancillary room plants may need to be interlocked to the theatre suite plant so that reverse air flow patterns do not occur 6 40 Generally the most satisfactory solution is to have a number of plants Spare motors should be provided but apart from this no provision for standby plant can
172. tory and discharging filtered air uni directionally over the work space 6 124 They protect the media from contamination but protection of the operator depends on the design of the cabinet and subsequent maintenance 6 125 Limitations on the use of Class Il cabinets are given in Categorisation of pathogens according to hazard and categories of containment Appendix A Arrangements for fume cupboard installations 6 126 The primary factors which contribute to the effective performance of fume cupboards include 84 HTM 2025 DC reprinted with amendments January 1999 6 0 Special ventilation systems e an adequate volume of supply air e an effective exhaust system to promote the safe dispersal of waste products to atmosphere 6 127 The air velocities through sash openings must be sufficient to prevent hazardous materials from entering the laboratory while avoiding excess flow rates that interfere with the investigation process Average face velocities should be between 0 5 and 1 0 m s with a minimum at any point within 20 of the average the upper end of the range being applicable to the containment of materials of high toxicity The design velocity must be maintained irrespective of whether the sash opening is varied or whether doors or windows are open or closed 6 128 The possibility of a fire or explosion which may not be contained by a fume cupboard must always be considered A fume cupboard should not therefore be sited in
173. ts e S final supply air flow rates f E final extract flow rates J SAwc air supply flow rate for air movement control h E air extract flow for air movement control AMC 1 4 To simplify the procedure standard worksheets WS1 to WS7 have been devised For each operating suite a set is required comprising one each of WS1 WS3 WS5 WS6 a WS6 b and WS7 one WS4 for each corridor and one of WS2 to cover each peripheral room WS2 has five versions WS2a single flow WS2b parallel series multi flow WS2c parallel multi flow or series multi flow unbalanced WS2d series multi flow balanced and WS2e Bay semi open Peripheral room types 1 5 The rooms in the operating suite other than the operating room and corridor are referred to as peripheral rooms Peripheral rooms have been classified according to the flows in and out These room classifications are under the headings below HTM 2025 DC reprinted with amendments January 1999 91 Appendix 1 Design of air movement control schemes for operating suites Step Description Worksheet 1 Show nominal room pressures and air flow directions on the plan fig C1 and WS1 WS1 AEE DAT SONS ERE RUE sp 2 Enter heat loss gain data and calculate supply air flow rates for temperature control WS1 only Categorise room types e g sterile clean etc rep 3 Enter air flows required for bacterial contamination control add supp
174. very room will be rather higher than that needed merely to provide clean comfortable conditions as it is necessary to control the level of anaesthetic gas pollution 15 air changes are recommended with a balanced air flow 6 47 Where possible the supply air terminals should be ceiling mounted above the recovery bed positions so that anaesthetic gas exhaled by recovering patients will be immediately diluted Ultra clean ventilation systems Special requirements 6 48 Ultra clean ventilation UCV systems installed in operating rooms can reduce the joint sepsis rate after total joint replacement surgery to approximately half that found in a conventionally ventilated operating room Clothing designed to reduce airborne bacteria dispersion total body exhaust gowns when used in UCV systems was shown to reduce the sepsis rate by half again The bacteria counts at the wound site associated with these results are approximately 10 m and 1 m respectively A minimum standard for the UCV has been suggested where the average count at the wound should not exceed 10 bacteria carrying particles m BCP m However it is also suggested that to ensure minimal or no contamination of the wound from the air an airborne concentration of no more than 1 BCP m would be required 6 49 Investigations have shown that different designs of UCV systems give different airborne bacteriological concentrations 6 50 Many design issues such as the merits of vertical
175. wirl in the airstream When the air spins in the same direction as the impeller the performance and power consumption of the fan are reduced When the air spins in the opposite direction to the impeller the power consumption and noise will increase with hardly any pressure increase Airstream swirl is usually induced by large variations across the fan inlet eye caused by the air passing round a tight bend immediately before the eye 4 38 For any condition in which a centrifugal fan is located with a free inlet the clear distance between the suction opening and the nearest wall should be not less than the diameter of the inlet If two fans with free inlets are positioned within the same chamber their adjacent suction openings should be at least 1 5 diameters apart HTM 2025 DC reprinted with amendments January 1999 37 4 0 Plant equipment selection Control 4 39 Fans in healthcare applications are generally either single or two speed Where there is a requirement for two speed operation this is generally via a local user control for example in a hood extract system to provide a boost facility or via a time schedule for energy saving during unoccupied periods 4 40 Where two speed operation is required twin supply fans may be preferred as they allow greater flexibility of plant control and avoid the need for spare motors to be provided If single speed fans are selected speed reduction will be required to reduce the flow rate by 509
176. y or comfort 2 23 Some types of window for example vertical sliding can enhance single sided air change by temperature difference and these will improve the overall rate of natural ventilation in protected or sheltered areas where the effect of wind pressure is likely to be minimal 2 24 Itis generally considered that cross flow ventilation is able to give reasonable air distribution for a distance of up to 6 metres inwards from the external facade provided that reasonably clear air paths are maintained Beyond this distance in areas where clear air paths cannot be maintained and in areas where high minimum air change rates are specified mechanical ventilation should be provided Section 2 3 of HTM 55 Windows BS5295 Code of Practice for Design of Buildings and CIBSE Symposium Natural Ventilation by Design 2 12 80 provide further information 2 25 Where natural ventilation is adopted with complex air paths the designer should produce an air flow diagram in order to ensure correct provision of air transfer devices Mechanical extract ventilation 2 26 Both foul and general extract systems can vary in complexity from a single wall mounted fan for each facility to a ducted air distribution system with dual extract fans 2 27 Replacement air is either provided by a central supply system as described below or enters the building through gaps in the structure or purpose made openings Unless special precaut

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