Radiant heating and cooling by embedded water-based
Contents
1. K hlung von Atrien 16 Internationaler Velta Kongre St Christoph Tirol Carli M de Peron F Romagnoni P Zecchin R 2000 Computer simulation of ceiling radiant heating and cooling panels and comfort evaluation Proceedings of Healthy Buildings Helsinki Carli M de Olesen B W 2001 Field measurements of thermal comfort conditions in buildings with radiant surface cooling systems Proceedings of Clima 2000 Naples CEN 199 Ventilation for Buildings Design Criteria for the Indoor Environment Brussels European Committee for Standardization CR 1752 DIN 1994 DIN 1946 1994 Raumlufttechnik Teil 2 Berlin Deutsches Institut f r Normung EN1264 1998 Floor heating Systems and components Fort K 1996 Type 160 Floor Heating and Hypocaust Hauser G Kempkes Ch Olesen B W 2000 Computer Simulation of the Performance of a Hydronic Heating and Cooling System with Pipes Embedded into the Concrete Slab between Each Floor ASHRAE Winter meeting Dallas 5 9 February 2000 Holst S and Simmonds P 1999 K hlkonzeption am Beispiel Flughafen Bangkok 21 Internationaler Velta Kongre St Christoph Tirol International Organization for Standardization 1993 Moderate Thermal Environments Determination of the PMV and PPD Indices and Specification of the Conditions for Thermal Comfort EN ISO Standard 7730 Knudsen H N et al 1989 Thermal Comfort in Passive Solar Buildings Technica2. floor 5 floor meeting all offices range C window window window window middle room except east south west east middle lt 20 0 0 1 2 0 0 0 0 0 0 0 0 0 2 20 22 11 2 34 5 2 5 1 4 20 4 35 7 17 1 22 25 88 6 64 4 75 0 11 7 12 6 63 8 12 1 25 26 0 1 0 0 18 4 21 7 7 0 0 5 8 1 26 27 0 0 0 0 3 7 5 2 0 0 0 0 1 8 gt 27 0 0 0 0 0 4 0 0 0 0 0 0 0 1 Table 10 Percentage of operative temperature distribution during working time heating period Temperature 4 floor 4 floor 5 floor 5 floor meeting all offices change window window window window room during a day east south west east C lt 20 0 11 0 1 0 0 2 2 20 22 55 3 75 1 34 18 1 29 9 42 5 22 25 44 7 13 9 65 9 81 9 70 1 55 3 gt 25 0 0 0 0 0 0 Building 3 Cooling period Operative 4th floor window east Operative 4th floor window south Operative 5th floor window east Operative 5th floor window west outside gt oO oO oa o amp oO fi N oO Temperature C ol 15 10 7 7 7 7 7 7 7 7 7 oO io io oO C je 2 o 2 o o o 2 o 2 o o oO N oO N oO N oO N oO N oO gt e gt s gt e gt s gt s N q X X Q X X N I RK S S x gt x nr 1O a oO N foe o gt N x N ite N oO N N N eo N N N N N N time Figure 6 Sample of temperature trend in a working week for cooling condi
3. 25 5 C and a lower class a range of 22 27 C In the German Standard DIN 1946 DIN 1944 1994 the operative temperature may increase up to 27 C and for higher outdoor temperatures up to 32 C Especially for high thermal mass systems it is important that comfort is specified as a range because with these systems the room temperature cannot be controlled at a fixed level As the heat transfer between the heated or cooled surfaces the space and people in the space is mainly by radiation it is important to use the operative temperature for specifying comfort conditions and for load calculations With concrete slab systems where the dynamic effects 2 and thermal storage capacity of the slabs are used the operative temperature during the day should be within the comfort range Studies by Knudsen et al 1989 show that as long as the temperature change is less than 5 K per hour the temperature range based on steady state conditions ISO 7730 is still valid Compared to air systems there will be fewer problems with draught and noise using water based slab heating and cooling systems Further comfort requirements are related to vertical air temperature differences radiant temperature asymmetry and too high or low surface temperatures Measurements with floor cooling Olesen 1997 show that even at a floor temperature of 10 K lower than the room temperature the vertical air temperature difference between head and feet is less than the requir
4. direct heating and cooling capacity depending on the distance between pipes the thickness above below pipes the surface material and the water temperature The heat exchange coefficient depends however on the position of surfaces wall ceiling floor and whether heating or cooling is used Olesen 1997 Olesen et al 2000 The heating and cooling capacities mentioned above are for systems where the pipes are positioned near the surface of ceiling or floor This will require water temperatures within the range 15 45 C depending on the construction of ceilings and floors If the humidity is not controlled the cooling capacity may be further reduced To obtain the same capacities with the pipes embedded in the centre of the concrete slabs an even wider water temperature range would be needed This would however make it almost impossible to control the system Therefore much lower capacities are possible with concrete slab systems It is therefore recommended to use these systems only if the loads are less than 50 W m In office buildings it is very common to use a raised floor for running cables In the case of concrete slab cooling most of the heat transfer will then be over the ceiling side which means suspended ceilings should not be used As the air systems only have to be sized for the ventilation rate needed for acceptable indoor air quality which means an air change rate of 1 to 2 h instead of 4 to 6 h the ducts will be muc
5. in a multi storey building de Carli and Olesen 2001 Long term measurements of operative air surface system and external temperatures have been carried out The results from one of the buildings are given below In this building an active thermal slab system of 6500 m was installed for heating and cooling The building had raised floors for the installation of cables but only a limited area with suspended ceiling and openable windows Mechanical ventilation was provided by a displacement system the supply air being pre cooled or heated to a temperature 1 3 degrees below room temperature Measurements have been made in two open space offices on the 4th and 5th floors during August 1999 from mid June to mid October 2000 and from December 2000 to January 2001 The outside temperature was also measured The water supply temperatures were controlled in the range 19 23 C from summer to winter according to the outside temperature The system was in operation only from 18 00 until 10 00 Cooling period A sample of operative temperature can be seen in Figure 6 for a typical warm working week From Table 9 it appears that for 95 of the total working time operative temperatures are between 21 C and 26 C From the tables it can be seen that temperatures on the 5 floor are higher than those on the on 4 floor This is because the two floors are connected by an open stairway in the middle of the landscape offices Therefore some of the convec
6. 3 C 21 23 C 21 24 C 22 23 C 21 23 C 21 24 C RE EN 0901 1 0901 8 0901 9 0901 1 0901 8 0901 9 dead band Ke lt 20 0 0 0 0 0 0 Operative 20 22 0 0 0 2 6 5 temperature 22 25 58 58 B8 81 78 69 interval 25 26 25 25 33 14 14 20 26 27 112 12 22 2 2 6 gt 27 5 5 7 0 0 0 Kl 0 0 0 0 1 2 5 5 5 19 19 19 ieper 2 3 44 44 44 31 31 32 3 4 51 51 51 49 49 48 drift days 4 5 0 0 0 1 1 1 5 6 0 0 0 0 0 0 gt 6 0 0 0 0 0 0 Pump running hours 1094 1094 878 709 657 378 of time30 30 24 19 18 10 Energy Cooling 1035 1035 983 669 657 606 KWh Heating 0 0 0 50 25 15 5 2 Study on room temperature dead band To minimize the risk for both heating and cooling within the same day and also to decrease pump running time it is recommended to let the building float within a certain room temperature interval i e dead band In the study by Olesen et al 2000 it was always 22 23 C In the present study two additional dead bands 21 23 C and 21 24 C were tested The results for the summer period are shown in Table 7 and for the winter period in Table 8 In all cases the supply water temperature was controlled according to case 901 with a constant ventilation rate of 0 8 ach for the whole day For the summer period dead bands of 22 23 C and 21 23 C gave the same results as regards operative temperature distribution energy use and pump running time The dead band 21 24 C resulted in a somewhat higher room te
7. 9 41 29 29 28 29 Tempe 2 3 21 21 20 23 12 12 13 13 3 4 2 2 0 4 2 2 1 2 drift days 4 5 0 0 0 0 0 0 0 0 5 6 0 0 0 0 0 0 0 0 gt 6 0 0 0 0 0 0 0 0 Hours 837 642 1487 1166 813 664 1533 1322 Pump running ie of time 16 13 29 23 16 13 30 26 Energy Cooling 144 144 143 143 57 64 63 45 KWh Heating 551 554 407 421 816 834 684 717 Also for the winter period Table 6 the cases 801 901 and 1401 result in the most comfortable conditions In Venice the room temperatures exceed the interval 20 24 C less than 12 of the time In case 1401 the room temperature is however below 20 C for 4 of the time On the energy side case 1401 is again about 10 better than cases 801 and 901 but the pump running time is significantly higher In winter the energy use in W rzburg is as expected higher than in Venice It is clear that with proper control the activated slab system is not only capable of reducing the indoor temperatures to a comfortable range but also as the only heating system of heating up the space to the comfort range Table 6 Operative temperatures temperature drift pump running time and energy transfer by different room temperature dead bands Control of water supply temperature according to outside and internal temperature case 0901 Summer conditions Ventilation rate 0 8 ach May to September Time of operation 18 00 06 00 Venice W rzburg Room 22 2
8. Radiant heating and cooling by embedded water based systems BJARNE W OLESEN PH D Technical University of Denmark International Centre for Indoor Environment and Energy Nils Koppels Alle DTU Building 402 2800 Lyngby Denmark e mail bwo mek dtu dk http www jie dtu dk ABSTRACT Because of high initial costs high energy consumption and often unacceptable indoor climate SBS noise draught some European countries do not recommend full air conditioning and sometimes even prohibit it Alternatively heating and cooling may be done by water based radiant heating and cooling systems where pipes are embedded in the building structure floors ceilings walls or in the centre of the concrete slabs in multi storey buildings The present paper will discuss the possibilities and limitations of radiant surface heating and cooling systems Differences in performance and application of surface systems compared to embedded systems are presented Results from both dynamic computer simulations and field measurements are presented The paper shows that for well designed buildings these types of system are capable of providing a comfortable indoor climate both in summer and in winter in different climatic zones Various control concepts and corresponding energy performance are presented To remove latent heat these systems may be combined with an air system This air system can however be scaled down with the benefit of improved comfort noise d
9. ant heating and cooling systems ASHRAE Tranactions v 100 Pt 1 Steimle 1999 Entwicklung der W rmepumpentechnik der Fu boden als Heiz und K hlfl che 21 Internationaler Velta Kongre St Christoph Tirol TRNSYS 1998 TRNSYS 14 2 User s Manual
10. ctive 50 radiant Moisture production during occupation 100 g h Ventilation ach outside time of occupation 0 3 h infiltration during occupation 1 5 h 11 V s per person Sun protection during occupation by direct exposure of sunlight and operative temperature above 23 C reduction factor z 0 5 4 3 Control parameters studied Three control parameters were studied e Control of water temperature e Dead band for room temperature e Use of weather forecast 4 3 1 Control of water temperature The goal for the system used in the present study was to operate water temperatures as close to the room temperature as possible If very high or very low water temperatures are introduced into the system it may result in over heating or under cooling In the present study the supply water temperature was controlled so that it was not lower than the dew point in the space For this purpose a humidity balance latent loads from people outside humidity gain from ventilation was also included in the simulation It was then possible to calculate the dew point in the room for each time step in the simulation Instead of controlling the supply water temperature it may be better to control the average water temperature The return water temperatures are influenced by the room conditions By 6 maintaining a constant supply water temperature an increase in internal loads from sun or internal heat sources will increase the return temperatu
11. d band analysis By optimizing the dead band the energy use for heating cooling and running the pump can be reduced without sacrificing comfort The dead band should not be greater than 2 K 5 3 Study on use of weather forecast The results in Figure 4 show the distribution of operative temperature during working time There is no significant difference between the cases So no benefits are obtained by trying to use a predicted future temperature In real life an additional factor will be how to correct the weather prediction So it may even be worse to use the predicted weather data as input for the control It should be mentioned that for the 24 or 72 hour average of the future outdoor temperature the water supply temperature is constant during the time of operation 18 00 to 06 00 Also when looking in detail at one week Figure 5 the same results are obtained independent of the way in which the outdoor temperature is used Table 8 Operative temperatures temperature drift pump running time and energy transfer by different room temperature dead bands Control of water supply temperature according to outside and internal temperature case 0901 Winter conditions Ventilation rate 0 8 ach October to April Time of operation 18 00 06 00 Venice W rzburg Room 22 23 C 21 23 C 21 24 C 22 23 C 21 23 C 21 24 C Das N
12. d via a special module developed by Fort 1996 The following describes the test space and other boundary conditions which were very similar to the conditions reported by Olesen et al 2000 and Hauser et al 2000 4 1 Description of system and test space The system considered is shown in Figures 2 and 3 The ceiling floor consists of an 18 cm thick concrete slab with 20 mm plastic pipes embedded in the middle with 150 mm spacing The slab is finished with 20 mm of acoustical insulation and 45 mm screed Heat is supplied or removed by the heated or cooled water flowing in the embedded pipes The mass flow rate of the system is constant at 350 kg h The effect of heating and cooling the ceiling is described using a central room module in an office building with offices on either side west and east of the corridor This characterizes the thermal behaviour of all rooms that are at least two rooms away from the roof corner and ground floor rooms The geometrical dimensions of the room module are shown in Figure 2 Detail CC OSC OD oC DO ee COO oO Oe Oe Oo oO Office Office Corridor Roomwidth 3 6 m Figure 2 Central room module used for the computer simulation of a building with concrete slab cooling All dimensions are in metres ER tes at Pts we BA D eV VNANNAAANAAMAMMANYANNAN oO Om S oF P 5 ER eel eco hee AL TITTEN Figure 3 Position of the plastic pi
13. e 0901 1 0901 8 0901 9 901 1 0901 8 0901 9 dead band aC lt 20 0 0 0 0 0 0 Operative 20 21 Jl 8 8 2 13 13 temperature 21 23 162 71 68 78 77 77 interval 23 24 127 13 12 16 7 7 24 26 J10 7 11 4 2 2 gt 26 0 0 0 0 0 0 lt 1 0 0 0 5 1 1 1 2 49 47 47 64 69 69 emp rt 2 3 43 44 44 22 22 22 drift days Zn i i i i i 4 5 0 0 0 0 0 0 5 6 0 0 0 0 0 0 gt 6 0 0 0 0 0 0 Pumptining hours 761 526 443 841 634 594 of time 15 10 9 17 12 12 Energy Cooling 101 83 61 33 19 11 KWh Heating 842 713 695 1194 1138 1113 Distibution of the operative temperatures in the worktime 700 4 case 18 600 To o case 21 500 case 24 4 400 300 200 100 Figure 4 Distribution of operative temperature during working time One week in october 30 25 P a case 18 case 18 D case 19 case 20 case 21 case 24 Toutdoor E 5 7 j 7 j 1 06 10 00 00 07 10 00 00 08 10 00 00 09 10 00 00 10 10 00 00 11 10 00 00 12 10 00 00 13 10 00 00 Figure 5 Operative temperature during a week in October 6 FIELD MEASUREMENTS Hundreds of buildings exist with embedded heating cooling systems To study the performance in real buildings some field measurements of thermal comfort conditions were made in several buildings with radiant surface systems floor wall and systems with pipes embedded in the concrete slabs between each floor
14. e building mass you will not only get a direct heating cooling effect but you will also due to the thermal mass reduce the peak load and transfer some of the load Ceiling Wall EEEREN AA Seen OOOO OOOO Figure 1 Examples of the positioning of pipes in floor wall ceiling and slab constructions outside the period of occupancy Because these systems for cooling operate at a water temperature close to room temperature they increase the efficiency of heat pumps ground heat exchangers and other systems using renewable energy sources The present paper will discuss the possibilities and limitations of radiant heating and cooling systems Especially results from studies on systems where pipes are embedded in the concrete slab between each storey of a building are presented These results are based on dynamic computer simulation and measurements in buildings during normal operation 2 THERMAL COMFORT The requirements for thermal comfort may limit the capacity and use of radiant surface heating and cooling systems Based on international standards and guidelines ISO 1993 CEN 1998 the thermal comfort requirements for people with mainly sedentary activity 1 2 met is in winter heating season 1 0 clo an operative temperature range of 20 24 C and in summer cooling season 0 5 clo 23 26 C In CR 1752 different classes of thermal environment may be specified A higher class has an operative temperature range of 23 5
15. ed 3 K The comfort requirements for radiant temperature asymmetry due to a heated ceiling is 5 K and for a cooled ceiling 14 K This will limit the acceptable ceiling temperature for heating to approximately 27 28 C For a cooled ceiling the dew point in the space and not the radiant asymmetry will limit the lower surface temperature The acceptable range for the floor temperature for people wearing shoes is 19 29 C However in spaces where people are mainly involved in sedentary activity it is recommended that the floor temperature be no less than 20 C 3 HEATING AND COOLING CAPACITY The important factors for the heating and cooling capacity of surface systems are the heat exchange coefficient between the surface and the room the acceptable minimum and maximum surface temperatures based on comfort and consideration of the dew point in the space and heat transfer between the pipes and the surface Table 1 Table 1 Heat exchange coefficient minimum and maximum recommended surface temperature and cooling and heating capacity Olesen 1997 Olesen 2000 Total heat exchange Surface temperature Capacity coefficient C W m W m K Heating Cooling Maximum Minimum Heating Cooling Floor Perimeter 11 7 35 20 165 42 Occupied zone 11 7 29 20 99 42 Wall 8 8 40 17 160 12 Ceiling 6 11 27 17 42 99 The heat exchange coefficient depends on the position of the surface and the surface temperature in relation t
16. h smaller and a suspended ceiling is not needed The air ducts and the main supply and return water pipes are then installed in the hallway between the offices The avoidance of suspended ceilings has the big advantage of reducing the total building height resulting in significant savings on construction costs and materials used Without the suspended ceiling the acoustical requirements must be solved in other ways 4 OPERATION AND CONTROL Even if surface heating and cooling systems often have a higher thermal mass than other heating cooling systems they have a high control performance This is partly due to the small temperature difference between the room and the system water surface and the resulting high degree of self control Studies on controllability of floor heating cooling Olesen 2001 show that floor heating control the room temperature as well as radiators To avoid condensation on a cooled surface there is a need to include a limitation on water temperature based on the space dew point temperature If however the pipes are embedded in the building structure it is often questioned how these systems should be controlled or operated Some studies deal with this issue Brunello et al 2000 Carli de et al 2001 Olesen 2002 In the following further results are presented A study was performed with the aid of the dynamic simulation program TRNSYS 1998 The multidimensional heat transfer processes in the slab were modelle
17. l University of Denmark Koschenz M and Dorer V 1996 Design of air systems with concrete slab cooling 5 International Conference on Air Distribution in Rooms Roomvent 96 Koschenz M 1998 Thermoaktive Bauteilsysteme Potentialabsch tzung und Erfahrungen Beitrag am 10 CH Status Seminar ETHZ 10 09 98 Z rich Meierhans R A and Olesen B W 1999 Betonkernaktivierung Book 67 pg ISBN 3 00 004092 7 Meierhans RA 1993 Slab cooling and earth coupling ASHRAE Transactions V 99 Pt 2 Meierhans R A 1996 Room air conditioning by means of overnight cooling of the concrete ceiling ASHRAE Transactions V 102 Pt 2 Olesen B W 1997 Possibilities and limitations of radiant floor cooling ASHRAE Transactions V 103 Pt 1 Olesen B W Michel E Bonnefoi F De Carli M 2000 Heat exchange coefficient between floor surface and space by floor cooling theory or a question of definition ASHRAE Transactions Part I Olesen B W 2001 Control of floor heating and cooling systems Clima 2000 Napoli 2001 World Congress Napoli September 2001 Olesen B W 2002 Control of slab heating and cooling systems studied by dynamic computer simulations AICARR conference Milan 2002 Simmonds P Gaw W Holst S Reuss S 2000 Using radiant cooled floors to condition large spaces and maintain comfort conditions ASHRAE Transactions Part I Simmonds P 1994 Control strategies for combined radi
18. mperature especially in Venice The pump running time decreased significantly but the energy use was about the same as for the two other dead bands In winter the greatest effect is achieved by lowering the dead band from 22 to 21 C This reduces the energy for heating by 20 and extends the time in which the operative temperatures are within the range 20 21 C although always higher than 20 Table 7 Operative temperatures temperature drift pump running time and energy transfer by different room temperature dead bands Control of water supply temperature according to outside and internal temperature case 0901 Summer conditions Ventilation rate 0 8 ach May to September Time of operation 18 00 06 00 Venice W rzburg Room 22 23 C 21 23 C 21 24 C 22 23 C 21 23 C 21 24 C RE EN 0901 1 0901 8 0901 9 0901 1 0901 8 0901 9 dead band C lt 20 0 0 0 0 0 0 Operative 20 22 0 0 0 2 6 5 temperature 22 25 58 58 38 81 78 69 interval 25 26 25 25 33 14 14 20 26 27 12 12 22 2 2 6 gt 27 5 5 7 0 0 0 lt 1 0 0 0 0 0 0 1 2 5 5 5 19 19 19 ieper 2 3 44 44 44 31 31 32 3 4 51 51 51 49 49 48 drift days 4 5 0 0 0 1 1 1 5 6 0 0 0 0 0 0 gt 6 0 0 0 0 0 0 Pump running hours 1094 1094 878 709 657 378 oftime 30 30 24 19 18 10 Energy Cooling 1035 1035 983 669 657 606 kWh Heating 0 0 0 50 25 15 Conclusions of the dea
19. o the room temperature heating or cooling While the radiant heat exchange coefficient is for all cases approximately 5 5 W m K the convective heat exchange coefficient will change The listed maximum surface temperature for the floor is based on the European standard for floor heating EN 1264 where it is permitted in the perimeter zonel m from outside walls to increase the maximum floor temperature to 35 C The maximum temperature for the wall is based on the pain limit for skin temperature approximately 42 C and the risk of being in contact with the wall over a longer period of time The maximum temperature of the ceiling is based on the requirement to avoid temperature asymmetry The minimum surface temperatures for wall and ceiling are based on consideration of the dew point and risk of condensation A special case for floor cooling is when there is direct sun radiation on the floor In this case the cooling capacity of the floor may exceed 100 W m B rresen 1994 This is also why floor cooling is increasingly used in spaces with large glass surfaces like airports Simmonds et al 2000 atriums and entrance halls The heat transfer between the embedded pipes and the surface of wall ceiling or floor will as long as there is no airspace in the construction follow the same physics It is then possible for all three type of surface to use the standard for floor heating CEN 1998 as the basis for design and calculation of the
20. pes in the concrete slab between two storeys The floor Figure 2 consists of 45mm screed 2 1 4 W m K c 1 kJ kgK p 2000 kg m3 20 mm insulation 4 0 04 W m K c 1 5 kJ kgK p 50 kg m and 180 mm concrete A 2 1W mK c 1kl kgK p 2400 kg m The outside pipe diameter is 20 mm and the spacing is 150 mm The window has a U value 1 4 W m K The room volume is 55 44 m with a thermal capacity of 700 kJ K 4 2 Boundary conditions The meteorological ambient boundary conditions correspond to those of W rzburg Germany and Venice Italy The external temperature data for winter and summer design days are shown in Table 2 Summer was the period from 1 May to 30 September and winter was the period from 1 October to 30 April Table 2 Design day outdoor temperatures for W rzburg Germany and Venice Italy l Lat Long Bley Heanng Dry Bulb Kopling Dry Bulb City ei a ar ra C 99 6 99 0 4 2 Venice 45 30 N 1220E 6 4 9 3 1 30 8 28 2 MUZDUrB 50 05N 8 60E 113 11 82 30 3 26 7 Frankfurt The time of occupancy was Monday to Friday from 8 00 to 17 00 with a lunch break from 12 00 to 13 00 The system was in operation only outside the period of occupancy from 18 00 to 06 00 Internal heat sources during occupied periods 550 W corresponding to 27 8 W m This corresponds to two occupants two computers a printer and light During the lunch break 350 W corresponding to 17 7 W m 50 conve
21. r temperature case 0801 or the average water temperature case 0901 is very small In the case of 1401 the control does not take into account the internal operative temperature but the results are almost identical to cases 0801 and 0901 With a constant average water temperature 22 C the cooling effect is too low and the operative temperature is often too high 60 of the time above 27 C in Venice and 27 in W rzburg The energy use is the same for the cases 0801 0901 and 1401 in Venice For W rzburg case 1401 is the energy use but it is about 10 lower than case 801 and 901 Energy use in case 1201 with a constant water temperature is relatively high The pump running time for case 1401 is equal to or lower than for the other cases In the summer case 1401 is overall better than the others Due to the warmer climate in Venice Table 3 the room temperatures are higher and energy use and pump running time are also higher compared to W rzburg Table 4 Operative temperatures temperature drift pump running time and energy transfer for different water temperature control strategies Summer conditions Dead band 22 23 C Ventilation rate 0 3 ach from 17 00 to 8 00 1 5 ach from 8 00 to 17 00 May to September Time of operation 18 00 06 00 Venice W rzburg Water Sn Be Aseas Ds Bene y pune genase Di outside outside 12 0 gt outside ou
22. raught compared to full air conditioning An added benefit can be reduced building height due to the elimination of suspended ceilings Finally surface heating and cooling systems use water at a temperature close to room temperature This increases the possibility of using renewable energy sources and increasing the efficiency of boilers heat pumps and refrigeration machines 1 INTRODUCTION In Europe it is mainly water based heating systems that are used These systems use radiators or floor heating as heat emitters One advantage compared with air systems is the more efficient means of transporting energy The demand for comfort better insulation of buildings and greater internal loads from people and equipment have increased interest in installing also a cooling system to keep indoor temperatures within the comfort range This resulted first of all in the introduction of suspended ceiling panels for cooling and in recent years also in the use of floor systems for cooling Holst and Simmonds 1999 Olesen 1997 Simmonds 1994 B rresen 1994 Typical positioning of pipes for wall floor and ceiling systems is shown in Figure 1 A new trend which started in the early nineties in Switzerland Meierhans 1993 1996 is to use the thermal storage capacity of the concrete slabs between each storey in multi storey buildings Pipes carrying water for heating and cooling are embedded in the centre of the concrete slab Figure 1 By activating th
23. re The average water temperature will then increase and the cooling potential will decrease If instead the average water temperature 2 treturn tsupply is controlled an increase in return temperature will automatically be compensated for by a decrease in supply water temperature In well designed buildings with low heating and cooling loads it may be possible to operate the system at a constant water temperature The following concepts for water temperature control were studied Supply water temperature is a function of outside temperature according to the equation 0 52 20 1 20 1 6 r 22 C case 801 Poy ly eben operative pP p Average water temperature is a function of outside temperature according to t 0 52 20 1 20 1 6 r 22 C case 901 average external operative Average water temperature is constant and equal to 22 C in summer and 25 C in winter case 1201 Supply water temperature is a function of outside temperature according to the equation 0 35 18 1 18 C summer case 1401 0 45 18 t 18 C winter case 1401 eup ply external Pain ply external 4 3 2 Dead band of room temperature To avoid a too frequent change between cooling and heating it is recommended that the circulation pump be stopped during a certain room temperature range i e dead band In the study by Olesen et al 2000 a dead band of 22 C to 23 C was used This means that when the room operative
24. re supply or average as a function of outdoor temperature There is no need to take into account the room temperature The actual outside temperature can be used as input to the control No benefits are obtained by using an average outdoor temperature or a future predicted outdoor temperature based on the weather forecast The energy performance energy use for heating and cooling pump running time can be reduced further by introducing a 2 K room temperature interval dead band where the circulation pump is stopped The system was able to keep the room temperatures within a comfortable range in both summer cooling and winter heating and in both climatic zones Due to the use of water temperatures close to room temperatures water based surface heating and cooling systems will increase the possibility to use renewable energy sources like ground source heat pumps ground heat exchangers geothermal energy solar energy evaporative cooling etc The level of water temperatures used also increase the efficiency of boilers chillers and heat pumps 7 REFERENCES ASHRAE 55 1992 Thermal Environmental Conditions for Human Occupancy Atlanta American Society of Heating Refrigerating and Air Conditioning Engineers Inc Brunello P Di Gennaro G De Carli M Zecchin R 2001 Mathematical modeling of radiant heating and cooling with massive thermal slab Proceedings of Clima 2000 Naples B rresen B 1994 Fu bodenheizung und
25. t and a west facing room Only results for a west facing room are presented in this paper In a pre test it was found that the highest exposures occurred in the room facing west Results from the summer period 1 May to 30 September and the winter period 1 October to 30 April are presented The total number of hours in each period is 3690 number of working days 109 and number of working hours 981 The results will be evaluated based on comfort operative temperature ranges daily operative temperature drift during occupancy and energy running hours for circulation pump energy removed or supplied by the circulated water The calculated operative temperatures may be compared to the comfort range 23 26 C recommended for summer cooling period and 20 24 C recommended for winter heating period ASHRAE 1992 CEN 1998 ISO 1993 This is based on a fixed level of clothing insulation for summer 0 5 clo and winter 1 0 clo which may not be relevant for the whole period 5 1 Study of water temperature control The results of the simulation are shown in Table 4 for summer conditions and in Table 5 for winter conditions The operative temperature of the cases 0801 0901 and 1401 Table 4 is for most of the time gt 85 in a comfort range 22 26 C In Wiirzburg 27 C is never exceeded and 26 C is exceeded less than 5 of the time In Venice only 5 of the temperatures are above 27 C The difference between controlling the supply wate
26. temperature increases above 23 C the system will start in the cooling mode If the room operative temperature is less than 22 C the system will start in the heating mode In between the circulation pump is stopped In the present study the following dead bands were tested 22 23 C case 0901 1 21 23 C case 0901 8 21 24 C case 0901 9 4 3 3 Use of weather forecast As the reaction time of the building and the activated slab is very long it may be an advantage to control the water temperature according to the weather forecast of external temperature By using a test reference year W rzburg or Venice the forecast can be made 100 correctly Table 3 shows the cases tested The supply water temperature tsup was controlled according to the outside temperature following the same algorithm but a different time average of external temperature tex was used as input The dead band was the same for all cases The simulation was made for the whole year Table 3 Boundary conditions case Water temperature External temperature dead band 18 Tsup 0 5 18 tex 18 Imean value next 24 hours 21 5 23 5 19 Tsup 0 5 18 tex 18 mean value next 72 hours 21 5 23 5 20 Tsup 0 5 18 te 18 mean value 12 hours around actual time 21 5 23 5 21 Tsu 0 5 18 tex 18 mean value 24 hours around actual time 21 5 23 5 ToajTan 03118103118 nstantveue iT 5 RESULTS AND DISCUSSION The simulations were made for both an eas
27. tions in Building 3 Building 3 Heating period 4th floor east side 4th floor south side 5th flooreast side 5th floor west side 24 23 5 23 an 22 5 fa Er d temperature C 9 pa J Ta wd 6 N N 21 5 20 5 20 19 5 19 08 01 01 0 00 08 01 01 6 00 08 01 01 12 00 08 01 01 18 00 09 01 01 0 00 09 01 01 6 00 09 01 01 12 00 09 01 01 18 00 10 01 01 0 00 10 01 01 6 00 10 01 01 12 00 10 01 01 18 00 11 01 01 0 00 11 01 01 6 00 11 01 01 12 00 11 01 01 18 00 12 01 01 0 00 12 01 01 6 00 12 01 01 12 00 12 01 01 18 00 13 01 01 0 00 time Figure 7 Sample of temperature trend in a working week for heating conditions in Building 3 16 6 CONCLUSIONS The use of surface heating and cooling using water based systems is becoming very popular Procedures for calculating the steady state heating cooling capacity are available By a proper control the risk for condensation on the cooled surfaces can be limited The results of a dynamic computer simulation of different control concepts for a water based radiant cooling and heating system with pipes embedded in the concrete slabs have been presented The system was studied for both the summer period May to September and the winter period October to April in two geographical locations Venice Italy and W rzburg Germany The best performance regarding comfort and energy is obtained by controlling the water temperatu
28. tive part of the internal loads on the 4 floor people equipment sun will rise to the 5 floor and increase the internal load there It can be seen that on some days the temperature in the morning is on the cool side As no subjective evaluations were made it is impossible to determine whether this caused a real comfort problem or not The low temperatures could probably be avoided by decreasing the number of hours of cooling operation during the night Heating period A example of the operative temperature can be seen in Figure 7 for a typical working week under heating conditions From Table 10 it can be seen that the operative temperatures are for most of the time within the comfort range suggested by the existing standards Except for the 4 floor south the measured operative temperatures are within the recommended comfort range in this position 11 of the time the temperature dropped below 20 C The building had an additional heating system installed which however has not been in operation The basic heating is made by the activated concrete slab system During the winter however the supply air temperature increased above the room temperature during the morning hours After 1 2 hours occupancy the supply temperature again decreased below room temperature Table 9 Percentage of operative temperature distribution during working time cooling period Temperature 4 floor 4 floor 5 floor 5
29. tside outside ie 0 e outside 0801 0901 1401 0801 0901 1401 ce lt 20 0 0 0 0 0 0 0 0 Operative 20 22 0 0 0 0 3 3 1 5 temperature 22 25 56 58 8 56 75 78 30 77 interval 25 26 26 25 13 25 18 16 21 14 26 27 113 12 19 14 5 4 22 4 gt 27 5 5 60 5 0 0 27 0 lt 1 0 0 0 0 3 2 6 4 1 2 9 9 14 10 26 27 26 24 TAD 2 3 56 54 65 49 33 33 46 35 3 4 B5 37 21 41 38 38 22 37 drift days 4 5 0 0 0 0 1 1 0 1 5 6 0 0 0 0 0 0 0 0 gt 6 0 0 0 0 0 0 0 0 Pump running hours 1254 1190 1417 1214 1091 971 1327 953 of time 34 32 39 33 30 26 36 26 Energy Cooling l 104 1109 1297 1106 763 785 978 749 KWh Heating l 2 0 0 29 41 2 2 Table 5 Operative temperatures temperature drift pump running time and energy transfer for different water temperature control strategies Winter conditions Dead band 22 23 C Ventilation rate 0 3 ach from 17 00 to 8 00 1 5 ach from 8 00 to 17 00 October to April Time of operation 18 00 06 00 Venice W rzburg Water p Ee a Average A verage SUBPIY nz Average RT Ss outside outside gt a a 2 outside outside n outside 0801 0901 0801 0901 1401 re lt 20 0 0 0 1 0 0 4 4 Operative 20 21 Jl 1 6 14 9 7 19 24 temperature 21 23 72 75 50 63 77 80 50 63 interval 23 24 14 15 5 14 8 7 7 7 24 26 12 10 23 8 6 5 15 2 gt 26 0 0 16 0 0 0 5 0 lt 1 33 34 30 32 57 57 58 57 1 2 44 43 4
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