Trane TRG-TRC010-EN User's Manual
Contents
1. Condensed liquid refrigerant collects in the bottom of the shell and flows through the liquid line to the expansion devices and economizer TRANE period one Components expansion device Orifice Plates orifice plates to gt evaporator Expansion Device An expansion device is used to maintain the pressure difference between the high pressure condenser and low pressure evaporator sides of the refrigeration system as established by the compressor This pressure difference allows the evaporator temperature to be low enough for the refrigerant to absorb heat from the water being cooled and the condenser temperature to be high enough for the refrigerant to reject heat to water at normally available temperatures High pressure liquid refrigerant flows through the expansion device causing a pressure drop that reduces the refrigerant pressure to that of the evaporator This pressure reduction causes a small portion of the liquid to boil off or flash cooling the remaining refrigerant to the evaporator temperature The expansion device is also used as a liquid refrigerant metering system balancing the refrigerant flow rate with the evaporator load condition In our example centrifugal chiller the expansion device used is a set of 2 orifice plates At full load a large amount of refrigerant is moving through the chiller The column of liquid refrigerant in the liquid line pressurizes the liquid at its base Dur2. and rating requirements WATER CHILLING PACKAGES A Scope USING THE VAPOR Factory designed and COMPRESSION prefabricated water chillers CYCLE Vapor compression refrigeration a Air cooled and water cooled condensing Equipment Certification Standards The Air Conditioning amp Refrigeration Institute ARI establishes rating standards for packaged HVAC equipment ARI also certifies and labels equipment through programs that involve random testing of a manufacturer s equipment to verify published performance The overall objective of ARI Standard 550 590 1998 is to promote consistent rating and testing methods for all types and sizes of water chillers with an accurate representation of actual performance It covers factory designed prefabricated water chillers both air cooled and water cooled using vapor compression refrigeration This generally includes chillers with centrifugal helical rotary screw reciprocating or scroll compressors equipment certification standards ARI Standard 550 590 a Standard rating conditions Common system conditions for published ratings Fouling factor a Integrated Part Load Value IPLV Part load efficiency rating Based on an average single chiller installation Standard operating conditions The standard rating conditions used for ARI certification represent typical design temperatures and flow rates for which water cooled and air cooled sy
3. Air Conditioning Clinic Centrifugal Water Chillers One of the Equipment Series TRG TRCO010 EN NO POSTAGE NECESSARY IF MAILED IN THE UNITED STATES BUSINESS REPLY MAIL POSTAGE WILL BE PAID BY ADDRESSEE a THE TRANE COMPANY Attn Applications Engineering E 3600 Pammel Creek Road La Crosse WI 54601 9985 bhbalabllalhonnnllhhahbhabhhhhalll NO POSTAGE NECESSARY IF MAILED IN THE UNITED STATES BUSINESS REPLY MAIL FIRST CLASS MAIL PERMIT NO 11 LA CROSSE WI POSTAGE WILL BE PAID BY ADDRESSEE THE TRANE COMPANY Attn Applications Engineering 3600 Pammel Creek Road La Crosse WI 54601 9985 Comment Card We want to ensure that our educational materials meet your ever changing resource development needs Please take a moment to comment on the effectiveness of this Air Conditioning Clinic Centrifugal Water Chillers One of the Equipment Series TRG TRCO010 EN About me Level of detail circle one Too basic Just right Too difficult Rate this clinic from 1 Needs Improvement to 10 Excellent Content 2 3 4 5 6 1 8 9 10 Booklet usefulness 2 3 4 5 6 7 8 9 10 Slides illustrations 2 3 4 5 6 7 8 9 10 Presenter s ability 2 3 4 5 6 7i 8 9 10 Training environment 2 8 4 5 6 7 8 9 10 Other comments Type of business Job function Optional name phone address Give the completed card to the presenter or drop it in the mail Thank you Respo
4. Review Period 2 2 stage compressor C evaporator enthalpy P expansion l devices economizer P _ 1 P Period 2 described the refrigeration cycle of 2 stage centrifugal water chillers with a pressure enthalpy chart The operation of the purge system for low pressure chillers was also presented Review Period 3 Ale PN D inlet vanes Period 3 further explained the operation of the centrifugal compressor It described the use of impeller inlet vanes as one method for controlling centrifugal compressor capacity Surge multistage compressors and adjustable frequency drives were also discussed TRG TRCO10 EN 49 TRANE 50 period six Review Review Period 4 a Maintenance considerations Operating log Mechanical components Heat transfer surfaces Fluid analysis Period 4 described the general maintenance requirements of a centrifugal water chiller including Recommended data for a daily log Required and recommended maintenance for mechanical components Recommended maintenance for heat transfer surfaces Required analyses for the oil and refrigerant Review Period 5 a Application considerations Condensing temperature control Constant or variable evaporator water flow Short evaporator water loops Heat recovery Free cooling Equipment certification standards Period 5 presented several considerations in the ap
5. inlet This pressure drop causes a portion of the liquid refrigerant to evaporate or flash and the resulting mixture of liquid and vapor enters the economizer chamber Here the vapor is separated from the mixture and is routed directly to the inlet of the second stage impeller The remaining liquid travels on to the second expansion device and evaporator Just before entering the evaporator the liquid refrigerant flows through a second expansion device that reduces its pressure and temperature to evaporator conditions Flashing a portion of the refrigerant prior to the economizer reduces the amount of compressor power required since the refrigerant vapor generated in the economizer only needs to be compressed by the second stage impeller The benefit of the economizer will be discussed in greater detail in Period 2 3 stage chiller Economizer refrigerant vapor refrigerant vapor to third stage to second stage of compression of compression liquid refrigerant to evaporator D orifice liquid refrigerant from condenser orifice In a chiller with a 3 stage compressor the expansion process can be separated into 3 steps with separate economizer chambers between the steps Liquid refrigerant from the condenser enters the first orifice expansion device which reduces the pressure of the refrigerant to that of the third stage impeller inlet This pressure drop causes a portion of the liquid refrigerant to flash and
6. Cycle 2 stage centrifugal chiller Refrigeration Cycle 2 stage compressor economizer m evaporator enthalpy l devices P Refrigerant leaves the evaporator as saturated vapor and flows to the first stage impeller of the compressor There the refrigerant vapor is compressed to a higher pressure P1 and temperature Cooler refrigerant vapor that flashed within the economizer is mixed with the refrigerant discharged from the first stage impeller reducing the heat content of the mixture The second stage of compression further elevates the pressure Pe and temperature of the refrigerant Energy provided to the compressor is imparted to the refrigerant as an increase in pressure and superheat Superheated refrigerant vapor leaves the compressor and enters the condenser Water flowing through the condenser absorbs heat from the hot high pressure refrigerant vapor causing it to desuperheat and condense into saturated liquid before leaving the condenser to travel to the first expansion device The first expansion device reduces the pressure to of the refrigerant to the second stage impeller inlet pressure P1 This pressure drop causes a portion of the liquid refrigerant to evaporate or flash The evaporating refrigerant absorbs heat from the remaining liquid refrigerant reducing its enthalpy from to The resulting mixture of liquid and vapor enters the ec
7. V is proportional to the product of impeller rotational speed and impeller diameter Therefore the static pressure producing capacity of a compressor can be adjusted by changing the flow rate of refrigerant the impeller speed or the diameter of the impeller TRG TRC010 EN TRG TRCO10 EN S TRANE period three Compressor Capacity Control Compressor Unloading full load part load Consider a given diameter compressor impeller that rotates at a constant speed As the load on the chiller decreases the inlet vanes partially close and the flow rate of refrigerant through the compressor drops Radial velocity V which is proportional to refrigerant flow decreases as well Even though the speed of rotation and diameter of the impeller are constant the tangential velocity V which is proportional to the product of impeller rotational speed and impeller diameter drops because of the pre swirling of the refrigerant caused by the inlet vanes The result is a shorter resultant velocity vector R which means that less static pressure is generated 25 TRANE 26 period three Compressor Capacity Control V lt static pressure As the load and the corresponding refrigerant flow rate continue to fall the radial velocity force drops too At some point the radial force becomes smaller than the generated static pressure letting the pressurized refrigerant vapor flow backward from the diffuser pa
8. a stiff bristled brush The loosened material is then flushed from the tubes with clear water As part of this procedure the strainers in both the chilled water and cooling tower water circuits should be cleaned every year Every 3 years more frequently in process or critical applications a qualified service organization should perform nondestructive inspections of the evaporator and condenser tubes The eddy current tube test is a common method Rarely problems may arise that cause refrigerant or water leaks These must be repaired immediately Fluid Analysis a Oil analysis Conduct annual analysis to verify system integrity Measure oil pressure drop to determine if filter needs changing Measure charge a Refrigerant charge Conduct analysis of refrigerant Inspect purge system Oil analysis is an important annual maintenance task required for centrifugal water chillers It may be conducted more frequently for chillers that run continuously or more often than normal This test performed by a qualified laboratory verifies the integrity of the refrigeration system by testing the concentrations of moisture acidity and metal This analysis can determine where problems exist or could potentially develop By taking oil samples on a regular basis normal operating trends for the compressor and bearing metals can be analyzed Instead of adopting a change the oil once a year whether it needs it or not approach reg
9. chiller on line and protecting the chiller from damage The limits for these different levels of protection should be obtained from the chiller manufacturer Short Evaporator Water Loops chilled water pump evaporator Short Evaporator Water Loops Proper chilled water temperature control requires that the temperature of the chilled water returning to the evaporator not change any faster than the chiller controls can respond The volume of water in the evaporator loop acts as a buffer ensuring that the return water temperature changes slowly and therefore providing stable temperature control If there is not a sufficient volume of water in the loop to provide an adequate buffer temperature control can be lost resulting in erratic system operation The chiller manufacturer should be consulted for volume requirements of the evaporator water loop TRG TRCO10 EN TRG TRCO10 EN S TRANE period five Application Considerations Short Evaporator Water Loops tank evaporator Short water loops may be unavoidable in close coupled or very small applications particularly in systems where the load consists of only a few air handlers or processes To prevent the effect of a short water loop a storage tank or large header pipe can be added to the system to increase the volume of water in the loop and ensure a slowly changing return water temperature A second solution is to reduce the water flow rate in t
10. rejects the heat of the refrigerant to water flowing through it 57 S i RANE Literature Order Number TRG TRCO10 EN File Number E AV FND TRG TRC010 999 EN The Trane Company 10 Worldwide Applied Systems Group Supersedes ae 3600 Pammel Creek Road Stocking Location Inland La Crosse La Crosse WI 54601 7599 www trane com An American Standard Company Since The Trane Company has a policy of continuous product improvement it reserves the right to change design and specifications without notice
11. the resulting mixture of liquid and vapor enters the high pressure chamber of the economizer Here the vapor is separated from the mixture and is then routed directly to the inlet of the third stage impeller The remaining liquid travels on to the second expansion device The second expansion device further reduces the pressure of the refrigerant to that of the second stage impeller inlet This pressure drop causes a portion of the liquid refrigerant to flash and the resulting mixture of liquid and vapor enters the low pressure chamber of the economizer Here the vapor is separated from the mixture and routed directly to the inlet of the second stage impeller The remaining liquid travels on to the third expansion device and evaporator TRG TRC010 EN S TRANE period one Components Again the final expansion device reduces the pressure and temperature of the refrigerant to evaporator conditions Evaporator tube bundle liquid refrigerant chilled Sr water return liquid 7 distributor eliminator orifice system Evaporator In the flooded shell and tube evaporator shown the low pressure mixture of liquid refrigerant and refrigerant vapor enters the distribution system that runs the entire length of the shell Small openings and baffles in the passage of the liquid distributor provide an even spray of refrigerant over the surfaces of the tubes inside the evaporator shell where the refrigerant absorbs heat from rel
12. 2 stage centrifugal chiller Refrigeration Cycle 2 stage compressor economizer le sannee ie evaporator condenser t expansion devices First let s review the components of a 2 stage centrifugal chiller in the context of the refrigeration cycle Refrigerant vapor leaves the evaporator and flows to the compressor where it is compressed to a higher pressure and temperature High pressure refrigerant vapor then travels to the condenser where it rejects heat to water and then leaves as a saturated liquid The pressure drop created by the first expansion device causes part of the liquid refrigerant to evaporate and the resulting mixture of liquid and vapor enters the economizer Here the vapor is separated from the mixture and routed directly to the inlet of the second stage impeller The remaining saturated liquid refrigerant enters the second expansion device TRG TRC010 EN 15 S TRANE 16 period two Refrigeration Cycle The pressure drop created by the second expansion device lowers the pressure and temperature of the refrigerant to evaporator conditions causing a portion of the liquid refrigerant to evaporate The resulting mixture of liquid and vapor enters the evaporator In the evaporator the liquid refrigerant boils as it absorbs heat from water and the resulting vapor is drawn back to the compressor to repeat the cycle Pressure Enthalpy p h Chart subcooled liquid mixture of pr
13. Centrifugal compressors use 1 or more impellers to compress the refrigerant A multistage compressor uses 2 or 3 impellers to increase the pressure of the refrigerant in steps instead of performing the task within a single impeller Compressed refrigerant vapor travels from the outlet of the first stage compressor impeller to the inlet of the second stage compressor impeller After TRG TRCO10 EN TRG TRCO10 EN S TRANE period one Components the accelerated refrigerant vapor leaves the last impeller it collects in the compressor volute and travels on to the condenser Condenser refrigerant vapor cooling tower water gt liquid tube refrigerant bundle gt Condenser The high pressure refrigerant vapor is discharged from the compressor into a heat exchanger that acts as a condenser In a water cooled condenser water is pumped through the tubes of the shell and tube heat exchanger while refrigerant vapor fills the shell space surrounding the tube bundle A baffle inside the condenser helps distribute the refrigerant evenly As heat transfers from the hot high pressure refrigerant vapor to the water refrigerant condenses on the tube surfaces Cooling water flows first through the lower tubes and then through the upper tubes This produces a nearly constant temperature difference between the downward moving refrigerant and the tube surfaces resulting in a uniform heat transfer rate within the tube bundle
14. FD or variable speed drive is another device used to vary the capacity of a centrifugal compressor AFDs are widely used with fans and pumps and with the advancement of microprocessor based controls for chillers they are now being applied to centrifugal water chillers Using an AFD with a centrifugal chiller can degrade the chiller s full load efficiency It will however offer energy savings by reducing motor speed at low load conditions when cooler condenser water is available An AFD also controls the inrush current at start up reducing stress on the compressor motor Certain system characteristics favor the application of an adjustable frequency drive including E A substantial number of part load operating hours m The availability of cooler condenser water Chilled water reset control m High electrical charges Performing a comprehensive energy analysis is the best method of determining if an adjustable frequency drive is desirable Depending on the application it may make sense to take the additional money needed to purchase an AFD and use it to purchase a more efficient chiller instead TRG TRCO10 EN 29 TRANE period four Maintenance Considerations Centrifugal Water Chillers period four Maintenance Considerations This period discusses general maintenance requirements of centrifugal water chillers Although some of the information applies specifically to the design presented in this clinic requiremen
15. able Evaporator Water Flow 39 Short Evaporator Water LOOPS cccceeseeeeeeeeeeees 40 Heat RECOVENY soeia iia aS 42 Free COGIING cicecresc conri R 44 Equipment Certification Standards c0cccee 46 period six REVIEW sere egea E cetinutaads 48 QuiZ eeir 52 Answers iiine 54 MOSSY 255555500 sdiesnsw Gaeahartahvisascctneuateiaidadatadaess 55 TRG TRCO10 EN iii S TRANE TRG TRC010 EN TRG TRCO10 EN Introduction Chilled Water System Water chillers are used in a variety of air conditioning and process cooling applications They are used to make cold water that can be transported throughout a facility using pumps and pipes This cold water can be passed through the tubes of coils to cool the air in an air conditioning application or it can provide cooling for a manufacturing or industrial process Systems that employ water chillers are commonly called chilled water systems centrifugal helical rotary There are several types of water chillers They differ from each other based on the refrigeration cycle or the type of compressor they use Absorption water chillers make use of the absorption refrigeration cycle and do not have a mechanical compressor involved in the refrigeration cycle S TRANE Introduction Water chillers using the vapor compression refrigeration cycle vary by the type of compressor used Reciprocating and scroll compressors are typically us
16. ants Hermetic Motor Cooling refrigerant z Another important difference in compressor motors is the issue of hermetic versus open A hermetic motor is totally enclosed within the chiller s refrigeration system An open motor is mounted externally outside of the TRG TRC010 EN TRG TRCO10 EN S TRANE period one Components chiller s refrigeration system and uses a coupling to connect the motor and compressor shafts The heat generated by the hermetic motor is absorbed by liquid refrigerant that flows around through and over the motor The heat must be rejected by the chiller s condenser The heat generated by the open motor is rejected to the air drawn in from the equipment room This heat must still be rejected from the equipment room either by mechanical ventilation or if the room is conditioned the building s cooling system In some designs this air is simply drawn into the motor housing by the rotating motor shaft The vent passages tend to get dirty and clog resulting in higher operating temperatures and hot spots that adversely affect motor efficiency and reliability Other designs such as totally enclosed fan cooled TEFC and totally enclosed air over TEAO use a separate fan with a protective housing to cool the motor Hermetic compressor motors eliminate the need for the shaft couplings and external shaft seals that are associated with open motors The coupling needs precise alignment and these s
17. apacity Control Multistage Compressor impellers 10 inlet vanes In a multistage centrifugal compressor the operating characteristics of each impeller are modulated by the impeller s own set of inlet vanes This example shows 2 impellers in series These impellers share the task of compressing the refrigerant Centrifugal water chillers are generally available with 1 2 or 3 impellers Impeller ee T a The forces that act on the refrigerant vapor within the centrifugal compressor impeller can be broken down into 2 components One component acts to move the refrigerant away from the impeller in a radial direction This component is called radial velocity V The second component acts to move the refrigerant in the direction of impeller rotation This component is called tangential velocity V Together these components generate the resultant velocity vector R the length of which is proportional to the amount of kinetic energy in the 23 TRANE 24 period three Compressor Capacity Control refrigerant Recall that kinetic energy is converted to static energy or static pressure Impeller Dynamics V lt refrigerant flow rate V rotational speed x diameter tat diameter na refrigerant rotationa flow rate speed The radial velocity Vr for a given compressor is directly proportional to the flow rate of refrigerant vapor through the compressor The tangential velocity
18. at to air drawn in from the equipment room orifice plate A type of expansion device that uses a fixed plate with holes drilled in it to reduce the pressure and temperature of the refrigerant to the conditions of the evaporator TRG TRCO10 EN TRG TRCO10 EN S TRANE Glossary pressure enthalpy chart A graphical representation of the saturated properties of a refrigerant plotting refrigerant pressure versus enthalpy purge A device used to remove air moisture and other noncondensable gases that may leak into a low pressure chiller refrigerant migration A method of free cooling that allows the chiller to be used as a heat exchanger without operation of the compressor It is possible when the condensing temperature of the refrigerant is low enough for refrigerant to migrate from the evaporator to the condenser refrigeration effect The amount of heat that each pound kg of liquid refrigerant will absorb when it evaporates starter A device used to connect and disconnect the chiller motor and the electrical distribution system surge A condition of unstable compressor operation where the refrigerant alternately flows backward and forward through the compressor impeller generating noise and vibration variable speed drive See adjustable frequency drive volute A large space around the perimeter of a centrifugal compressor that collects refrigerant vapor after compression water cooled condenser A type of condenser that
19. ate An economizer can be used to enhance the efficiency of a chiller with multiple compressor impellers A control panel is also provided on the chiller and a starter is either mounted on the chiller or located remotely TRG TRCO10 EN 3 TRANE period one Components Compressor Compressor The centrifugal compressor uses the principle of dynamic compression which involves converting energy from one form to another to increase the pressure and temperature of the refrigerant It converts kinetic energy to static energy Impeller blades The core component of a centrifugal compressor is the rotating impeller The center or eye of the impeller is fitted with blades that draw refrigerant vapor into radial passages that are internal to the impeller body TRG TRC0O10 EN TRG TRCO10 EN period one Components Centrifugal Compressor volute diffuser passage impeller passages The rotation of the impeller causes the refrigerant vapor to accelerate within the impeller passages increasing its velocity and kinetic energy The accelerated refrigerant vapor leaves the impeller and enters the diffuser passages These passages start out small and become larger as the refrigerant travels through them As the size of the diffuser passages increases the velocity and therefore the kinetic energy of the refrigerant decreases The first law of thermodynamics states that energy is not destroyed on
20. atively warm water flowing through the tube bundle This transfer of heat boils the liquid refrigerant on the tube surfaces The resulting vapor passes through an eliminator that prevents liquid from being drawn upward The vapor collects in a large chamber at the top of the shell and is drawn back to the compressor The now cool water can be used in a variety of comfort or process applications Some chiller designs may make use of a direct expansion DX shell and tube evaporator In this type of evaporator liquid refrigerant flows through the tubes and water fills the surrounding shell As heat is transferred from the water to the refrigerant the refrigerant boils inside the tubes and the resulting vapor is drawn to the compressor TRG TRCO10 EN 11 12 TRANE period one Components gear drive impeller impellers direct drive Motor A motor is used to rotate the impeller s A direct drive motor is connected directly to the impeller shaft and the impeller rotates at the same speed as the motor A gear drive motor transfers its energy to the impeller shaft using a set of gears This allows the impeller to rotate at a higher speed than the motor The direct drive motor requires fewer bearings and does not incur gear losses Additionally since the compressor rotates at a lower speed it can be much quieter Direct drive compressors are however only practical in centrifugal chillers that use low pressure refriger
21. ce the pressure and temperature of the refrigerant flash The process of liquid refrigerant being vaporized by a sudden reduction of pressure flooded shell and tube evaporator A type of evaporator where water flows through the tubes and refrigerant fills the surrounding shell gear drive motor A type of motor that transfers its energy to the impeller shaft using a set of gears allowing the impeller to rotate at a higher speed than the motor hermetic motor A type of motor that is totally enclosed within the chiller s refrigeration system and rejects its heat to the liquid refrigerant impeller The rotating component of a centrifugal compressor that draws refrigerant vapor into its internal passages and accelerates the refrigerant as it rotates increasing its velocity and kinetic energy inlet vanes A device used to vary the capacity of a centrifugal compressor by pre swirling the refrigerant in the direction of rotation before it enters the impeller lessening its ability to take in the refrigerant vapor loop time The amount of time it takes a particle of water to travel through the chilled water loop multistage centrifugal compressor A centrifugal compressor that uses more than 1 impeller to share the task of compressing the refrigerant open motor A type of motor that is mounted externally outside of the chiller s refrigeration system and uses a coupling to connect the motor and compressor shafts It rejects its he
22. eals are a prime source of oil and refrigerant leaks On the other hand if a motor burns out a hermetic chiller will require thorough cleaning while a chiller with an open motor will not Controls and Starter starter Controls and Starter A microprocessor based control panel is provided on the chiller to provide accurate chilled water control as well as monitoring protection and adaptive limit functions These controls monitor chiller operation and prevent the chiller from operating outside its limits They can compensate for unusual operating conditions keeping the chiller running by modulating system components rather than simply shutting it down when a safety setting is violated When serious problems occur diagnostic messages aid troubleshooting Modern control systems not only provide accurate optimized control and protection for the chiller but can also interface with a building automation system for integrated system control In a chilled water system optimal 13 TRANE 14 period one Components performance is a system wide issue not just a matter of chiller design and control A starter links the chiller motor and the electrical distribution system Its primary function is to connect start and disconnect stop the chiller from line power similar to what a switch does for a light bulb The starter however handles much more current and must have the appropriate interlocks to work with the chiller c
23. ed in small chillers Helical rotary or screw compressors are typically used in medium sized chillers Centrifugal compressors are typically used in large chillers As mentioned earlier this particular clinic discusses centrifugal water chillers Centrifugal Water Chillers Centrifugal water chillers can also be divided into two types based on the method used to reject heat to the atmosphere water cooled or air cooled Since most centrifugal chillers are water cooled they are the primary focus of this clinic Water cooled centrifugal chillers are generally available from 100 to 3 000 tons 350 to 10 500 kW as prefabricated machines and up to 8 500 tons 30 000 kW as built up machines TRG TRCO10 EN period one Components Centrifugal Water Chillers period one Components Many of the components of the centrifugal water chiller are similar to those of other chiller types components of a Centrifugal Water Chiller starter control panel evaporator This particular centrifugal water chiller makes use of a shell and tube evaporator where refrigerant absorbs heat from the water flowing through the tubes The compressor is made up of 1 or more centrifugal impellers A second shell and tube heat exchanger serves as the water cooled condenser where refrigerant is condensed inside the shell and water flows inside tubes Refrigerant is metered through the system using an expansion device such as a fixed orifice pl
24. eft to increase this refrigeration effect Also in a chiller without an economizer all of the refrigerant vapor must go through both stages of compression to return to condensing conditions In a chiller with an economizer refrigerant vapor that flashes in the economizer bypasses the first stage of compression resulting in an overall energy savings of 3 to 4 percent TRG TRC010 EN TRG TRCO10 EN S TRANE period two Refrigeration Cycle Refrigerant Operating Pressures HCFC 22 HFC 134a pressure HCFC 123 atmospheric pressure temperature Refrigerants When selecting which refrigerant to use in a centrifugal water chiller the manufacturer considers efficiency operating pressures compatibility with materials heat transfer properties stability toxicity flammability cost availability and environmental impact Refrigerants commonly used in centrifugal chillers can be classified as low medium or high pressure based on the normal operating pressures in the refrigeration cycle Chillers using a high pressure refrigerant like HCFC 22 or a medium pressure refrigerant like HFC 134a operate at pressures that are well above atmospheric pressure As we are about to see some sections of chillers that use a low pressure refrigerant such as HCFC 123 operate at below atmospheric pressure 19 20 period two Refrigeration Cycle TRG TRCO10 EN TRG TRCO10 EN S TRANE period three Compressor C
25. ements This method of free cooling involves using outdoor air for cooling instead of recirculating warmer indoor air It is the most efficient method of free cooling because it allows all of the chilled water and or refrigeration system components to be turned off This method however requires larger duct systems to deliver the outdoor air to the air handler and to return and exhaust this larger amount of air A second method of applying free cooling is to pump water from the cooling tower loop directly into the chilled water loop when its temperature is low enough to satisfy the cooling load This is commonly called the strainer cycle because a strainer or filter is needed to prevent debris and contaminants carried by the cooling tower water from entering the chilled water loop Although this method is very efficient the contamination common in open cooling tower systems causes concern about fouling deposits of scale or sludge inside the chilled water coils Ongoing treatment of the chilled water loop is required Another method of providing free cooling is similar to the strainer cycle but involves the use of a plate and frame heat exchanger or water side economizer to isolate the chilled water loop from the cooling tower loop This is a popular method of free cooling because it is efficient and eliminates potential contamination of the chilled water loop In addition the heat exchanger can be operated simultaneously with the chi
26. ent of microprocessor based controls the control panel and auxiliary controllers require no recalibration or maintenance Remotely mounted electronic sensors send information to the unit controller which can be connected to a building automation system to communicate information and allow system level optimization These systems can notify the operator with an alarm or diagnostic message when a problem occurs As for any mechanical equipment a daily visual inspection of the chiller is recommended to look for oil leaks condensation loosened electrical or control wiring or signs of corrosion Special attention should be given to safety controls and electrical components A qualified service technician should check the chiller annually for leaks The United States Environmental Protection Agency EPA mandates refrigerant recovery whenever a refrigeration circuit is opened during the normal service of any air conditioning system 32 TRG TRCO10 EN TRG TRCO10 EN S TRANE period four Maintenance Considerations maintenance considerations Mechanical Components a Other design specific requirements Change oil when oil analysis dictates Replace oil filter periodically Replace filter drier periodically Clean oil strainers annually Check shaft alignment annually Check coupling annually Replace shaft seal every 2 to 4 years Compressor teardown inspection every 5 to 10 years Some centrifugal compressor designs do r
27. equire periodic maintenance of mechanical system components This includes oil and refrigerant filter changes oil strainer changes and a compressor inspection Open motor compressor designs require shaft alignment coupling inspection bearing lubrication and cleaning of the motor windings on a quarterly or annual basis In all cases strictly follow the maintenance requirements and recommendations published by the manufacturer maintenance considerations Heat Transfer Surfaces a Recommended maintenance Use a qualified water treatment specialist Clean condenser tubes as needed Clean water side strainers Test tubes every 3 years To ensure optimum heat transfer performance the heat transfer surfaces must be kept free of scale and sludge Even a thin deposit of scale can substantially reduce heat transfer capacity Engage the services of a qualified water treatment specialist to determine the level of water treatment required to remove contaminants from the cooling tower water 33 Tane 34 period four Maintenance Considerations Scale deposits are best removed by chemical means During this process the water cooled condenser is commonly isolated from the rest of the cooling tower water circuit by valves while a pump circulates cleaning solution through the condenser tubes Sludge is removed mechanically This typically involves removing the water boxes from the condenser and loosening the deposits with
28. essure liquid and vapor 5 psia PEETA Fa A of TEET TY As B superheated 0 034 MPa 7 vapor 15 5 Btu lb 92 4 Btu lb 201 0 kj kg 380 4 kj kg enthalpy The pressure enthalpy chart plots the properties of a refrigerant refrigerant pressure vertical axis versus enthalpy horizontal axis Enthalpy is a measure of the heat content both sensible and latent per pound kg of refrigerant For example A represents the heat content of saturated liquid HCFC 123 refrigerant at 5 psia 0 034 MPa and 34 F 1 1 C B represents the heat content of saturated vapor HCFC 123 refrigerant at the same pressure and temperature The difference in heat content or enthalpy between A and B that is 76 9 Btu pound 179 4 kJ kg is the amount of heat required to transform 1 pound of saturated liquid refrigerant to saturated refrigerant vapor at the same pressure and temperature If the heat content of the refrigerant at any pressure falls to the right of the curve the vapor is superheated Similarly if the heat content of the refrigerant falls to the left of the curve the liquid is subcooled Finally when the heat content of the refrigerant falls inside the curve the refrigerant exists as a mixture of liquid and vapor Let s plot the theoretical vapor compression refrigeration cycle for a 2 stage centrifugal water chiller on a pressure enthalpy chart TRG TRCO10 EN TRG TRCO10 EN S TRANE period two Refrigeration
29. f the Standard explains this further The IPLV equation was derived to provide a representation of the average part load efficiency for a single chiller only However it is best to use a comprehensive analysis that reflects actual weather data building load characteristics operational hours economizer capabilities and energy drawn by auxiliaries such as pumps and cooling towers when calculating the chiller and system efficiency This becomes increasingly important with multiple chiller systems because individual chillers operating within multiple chiller systems are more heavily loaded than single chillers within single chiller systems Remember that the ARI rating is a standardized representation Many chillers do not run at standard rating conditions and few are applied in single chiller installations Performing a comprehensive energy analysis is the best method of comparing the system operating cost difference between 2 chillers 47 TRANE period six Review Centrifugal Water Chillers period six Review Let s review the main concepts that were covered in this clinic on centrifugal water chillers Review Period 1 compressor condenser Starter control panel evaporator Period 1 introduced the following components of a centrifugal water chiller compressor condenser expansion device economizer evaporator motor control panel and starter 48 TRG TRCO10 EN period six Review
30. f the refrigerant prior to entering the evaporator the economizer reduces the compressor power required since the refrigerant vapor generated in the economizer only needs to be compressed by the higher stage impeller A hermetic motor is totally enclosed within the chiller s refrigeration system and the heat it generates is absorbed by liquid refrigerant An open motor is mounted externally outside of the chiller s refrigeration system and uses a coupling to connect the motor and compressor shafts The heat generated by the open motor is rejected to the air drawn in from the equipment room a first stage of compression or first stage impeller b economizer c evaporator low pressure chiller purge system radial velocity V tangential velocity V inlet vanes and adjustable frequency or variable speed drive 10 The heat transfer tube surfaces inside the chiller must be kept free of scale and sludge to ensure optimum performance Even a thin deposit of scale can substantially reduce heat transfer capacity 11 higher lower 12 it is used to more closely predict actual chiller performance by accounting 54 for the effect of impurities in the chilled and condenser water systems These impurities will eventually deposit on evaporator and condenser tube surfaces impeding fouling heat transfer TRG TRC010 EN TRG TRCO10 EN TRANE Glossary adjustable frequency drive AFD A device used to vary the capac
31. he chilled water loop while using the same size pipes This also increases the loop time the time it takes a particle of water to travel through the chilled water loop and ensures that the return water temperature changes slowly This solution has the added benefit of reduced pumping energy requirements 41 Tane 42 period five Application Considerations Heat Recovery heat recovery condenser G3 cooling amp gy tower SS water gt a standard condenser Heat Recovery Salvaging usable heat from the refrigeration cycle heat that would normally be rejected to the atmosphere can significantly reduce the operating costs of many buildings Heat recovery is most commonly accomplished using 2 condensers and the fact that hot refrigerant vapor migrates to the area with the lowest temperature Raising the refrigerant condensing temperature in the standard condenser prompts the refrigerant to flow instead to the second condenser where it rejects its heat to the water flowing through the tubes The condensing temperature in the standard condenser is controlled by varying the temperature or the flow rate of the cooling tower water Typical uses for the hot water from the second condenser include heat for spaces around the perimeter of the building reheat coils in air conditioning systems and bathroom laundry or kitchen requirements Any building with a simultaneous heating and cooling load is a potent
32. ial candidate for heat recovery TRG TRCO10 EN S TRANE period five Application Considerations Heat Recovery Chiller Options heat recovery auxiliary dual condenser condenser heat pump Second full Second smaller No extra size condenser size condenser condenser Large heating Preheating loads Large base heating loads loads or continuous Moderate ration High hot water hot water operatio temperatures temperatures High hot water Controlled Uncontrolled temperatures Degrades e Improves chiller Controlled chiller efficiency efficiency Chiller efficiency preserved Three types of heat recovery chillers are commonly available The dual condenser or double bundle heat recovery chiller contains a second full size condenser that serves a separate hot water loop It is capable of more heat rejection and higher leaving water temperatures This type of chiller allows the amount of heat being rejected to be controlled although chiller efficiency is sacrificed for higher hot water temperatures Similarly an auxiliary condenser heat recovery chiller makes use of a second smaller condenser bundle It is not capable of rejecting as much heat as the dual condenser chiller Since its leaving water temperatures are also lower it is typically used to preheat returning hot water before it goes to the primary heating equipment or to preheat incoming water prior to entering a traditional water heater It require
33. ing passage through the orifice plates the liquid refrigerant undergoes a pressure drop equal to the head H1 before some of it flashes to vapor TRG TRCO10 EN TRG TRCO10 EN period one Components expansion device Orifice Plates orifice plates to gt evaporator As the load decreases less refrigerant moves through the chiller and the level of the liquid column drops Now as the liquid refrigerant passes through the orifice plates it only undergoes a pressure drop equal to the lower head H2 before some of it flashes to vapor This causes additional flashing at the orifice plate which in turn feeds less liquid to the evaporator Other types of expansion devices found in centrifugal chillers include float valves expansion valves thermostatic or electronic and variable orifices 2 stage chiller Economizer refrigerant vapor P to second stage of compression liquid refrigerant to evaporator D orifice liquid refrigerant from condenser Economizer An economizer can be used in conjunction with multiple expansion devices to improve the efficiency of a multistage chiller In a chiller with a 2 stage compressor the expansion process can be separated into 2 steps with an economizer chamber between S TRANE 10 period one Components Liquid refrigerant from the condenser enters the first expansion device which reduces the pressure of the refrigerant to that of the second stage impeller
34. isory documents published by the American Society of Heating Refrigerating and Air Conditioning Engineers ASHRAE This guideline includes a list of recommended data points to be logged daily for each chiller Much of this data may be available from the display on the chiller control panel Special attention should be given to Reviewing the operating log and trends Observing the oil pressure drop to determine if the oil filter needs to be replaced Monitoring evaporator and condenser approach temperatures Observing and recording the oil level Monitoring purge pump out operation 31 Tane period four Maintenance Considerations maintenance considerations Mechanical Components a Required maintenance Compressor and motor no maintenance required Controls no maintenance or calibration required a Recommended maintenance Visually inspect overall unit Inspect safety controls and electrical components Tighten electrical connections Check for leaks The compressor motor assembly in direct drive hermetic compressor designs requires little periodic maintenance The hermetic motor eliminates the need for external shaft seals associated with open motors These seals are a prime source of oil and refrigerant leaks and should be inspected on a regular basis Hermetic motor designs also eliminate the annual coupling and seal inspections alignment and shaft seal replacement associated with open motors With the adv
35. ity of a centrifugal compressor by varying the speed of the motor that rotates the impeller s air side economizer A method of free cooling that involves using cooler outdoor air for cooling instead of recirculating warmer indoor air ARI Air Conditioning amp Refrigeration Institute ARI Standard 550 590 A publication titled Standard for Water Chilling Packages Using the Vapor Compression Cycle used to promote consistent rating and testing methods for all types and sizes of water chillers It covers factory designed prefabricated water chillers both air cooled and water cooled using the vapor compression refrigeration cycle ASHRAE American Society of Heating Refrigerating and Air Conditioning Engineers ASHRAE Guideline 3 A publication titled Reducing Emission of Halogenated Refrigerants in Refrigeration and Air Conditioning Equipment and Systems that includes a recommended list of data points to be logged daily for each water chiller compressor The mechanical device used by the chiller to increase the pressure and temperature of the refrigerant vapor condenser The region of the chiller where refrigerant vapor is converted to liquid as it rejects heat to water or air control panel The microprocessor based panel that monitors the chiller s operation protects it from damage provides the operator with data and diagnostic messages and permits interfacing with a building automation system diffuser passages Pa
36. ller 44 TRG TRCO10 EN TRG TRCO10 EN S TRANE period five Application Considerations free cooling Refrigerant Migration from compressor condenser to compressor evaporator This leads to the discussion of a free cooling principle called refrigerant migration It involves adapting a water chiller so that it functions as a simple heat exchanger When the available condenser water is cooler than the desired chilled water temperature the compressor is turned off and bypass valves in the chiller refrigerant circuit are opened to let the refrigerant circulate without help from the compressor Because refrigerant migrates to the area with the lowest temperature refrigerant boils in the evaporator and the vapor flows to the cooler condenser bundle After the refrigerant condenses it flows by gravity back to the evaporator The advantages of refrigerant migration are these no extra components are required in the system control is performed by the chiller itself and there are no additional fouling concerns It is possible for the free cooling chiller to satisfy many cooling load requirements without operating the compressor especially when the system can accommodate warmer chilled water temperatures at part load conditions 45 46 TRANE period five Application Considerations equipment certification standards ARI Standard 550 590 a Purpose Establish definitions testing STANDARD for
37. ly converted from one form to another Thus the refrigerant s kinetic energy is converted to static energy or static pressure Refrigerant now at a higher pressure collects in a larger space around the perimeter of the compressor called the volute The volute also becomes larger as the refrigerant travels through it Again as the size of the volute increases the kinetic energy is converted to static pressure Due to its pressure and temperature the refrigerant leaving the compressor is in a condition that allows its heat to be rejected from the chiller TRANE period one Components centrifugal compressor Energy Conversion refrigerant enters 2 diffuser 8 g f EDA refrigerant refrigerant l enters impeller path through compressor enters volute Again in the passages of the rotating impeller the refrigerant vapor accelerates increasing its velocity and kinetic energy As the area increases in the diffuser passages the velocity and therefore the kinetic energy of the refrigerant decreases This reduction in kinetic energy is offset by an increase in the refrigerant s static energy or static pressure Finally the high pressure refrigerant collects in the volute around the perimeter of the compressor where further energy conversion takes place The resulting pressure and temperature of the refrigerant is now high enough that its heat can be rejected from the chiller Multistage Compressor
38. ng programs and field experience The Trane Air Conditioning Clinic series is one means of knowledge sharing It s intended to acquaint a nontechnical audience with various fundamental aspects of heating ventilating and air conditioning We ve taken special care to make the clinic as uncommercial and straightforward as possible Illustrations of Trane products only appear in cases where they help convey the message contained in the accompanying text This particular clinic introduces the concept of centrifugal water chillers 1999 American Standard Inc All rights reserved TRG TRCO10 EN Contents Introduction ooo ccc cc ccc ct eteeteees 1 period one Components iiei 3 COMPESSOP ociscmninnisdsnanbediscconss daisoanenuneneneneddoedunnoinus 4 CONGEMSE saniaisia Sonne teabassuaaich undelete ENERE EES 7 Expansion Device cceccceeeeeeeeeeeeeeeeeeeeeeeeeeeeeeaaes 8 ECONOMIIZET nerca AAEE 9 Evaporator srsermiencrceninitniann einna aana 11 MOTON sotineen ae iR 12 Controls and Starter ocssssssrrirrsr tiair 13 period two Refrigeration Cycle 00 15 RefigeraN S sessin iiaii as Ses aise 19 Purge SYSTEM rsrsr irinn assssiniii niaan 20 period three Compressor Capacity Control 22 period four Maintenance Considerations 30 period five Application Considerations 36 Condensing Temperature Control c0ccceeeee 37 Constant or Vari
39. nse Card We offer a variety of HVAC related educational materials and technical references as well as software tools that simplify system design analysis and equipment selection To receive information about any of these items just complete this postage paid card and drop it in the mail Education materials Software tools Periodicals Other Air Conditioning Clinic series Engineered Systems Clinic series Trane Air Conditioning Manual Trane Systems Manual Equipment selection System design amp analysis Engineers Newsletter Thank you for your interest The Trane Company Worldwide Applied Systems Group 3600 Pammel Creek Road La Crosse WI 54601 7599 www trane com An American Standard Company About me Name Title Business type _ Phone fax E mail address _ Company Address TRANE The Trane Company Worldwide Applied Systems Group 3600 Pammel Creek Road La Crosse WI 54601 7599 www trane com An American Standard Company Centrifugal Water Chillers One of the Equipment Series A publication of The Trane Company Worldwide Applied Systems Group S TRANE Preface Centrifugal Water Chillers A Trane Air Conditioning Clinic The Trane Company believes that it is incumbent on manufacturers to serve the industry by regularly disseminating information gathered through laboratory research testi
40. nt This minimum pressure difference depends on the chiller s design and controls The most common method of maintaining this pressure difference at various load conditions is to control the condensing temperature by varying the temperature or flow rate of water through the condenser By controlling condensing temperature most centrifugal water chillers can start and operate over a wide range of conditions Controlling condensing temperature 1 maintains chiller efficiency 2 maintains the required pressure differential between the evaporator and condenser for controlled flow through the refrigerant metering system and 3 prevents the pressure imbalance that could cause oil loss problems TRG TRCO10 EN 37 Tane period five Application Considerations condensing temperature control Cooling Tower Bypass diverting valve 65 F 18 C Controlling the refrigerant pressure difference between the evaporator and condenser of a water cooled chiller is accomplished by varying the temperature or flow rate of the water flowing through the condenser The following are 5 common methods used to control condensing temperature 1 Cycling or varying the speed of the cooling tower fans to control the temperature of the water leaving the cooling tower 2 Using a cooling tower bypass pipe to mix warmer leaving condenser water with the colder tower water and control the temperature entering the condenser as illustrated here 3 Mod
41. nverts energy to energy 2 Does the refrigerant velocity increase in the impeller diffuser passages or volute of the compressor 3 What is the benefit of using an economizer cycle with a multistage centrifugal compressor 4 What is the difference between a hermetic and an open motor Questions for Period 2 pressure enthalpy 5 Using the pressure enthalpy diagram in Figure 71 identify the following process of the 2 stage centrifugal chiller s refrigeration cycle a to b to c to 6 Air moisture and other noncondensable gases are removed from a pressure chiller by what component Questions for Period 3 7 What velocity component is directly proportional to the refrigerant flow rate through the compressor TRG TRC010 EN TRANE Quiz 8 What velocity component is directly proportional to the impeller s rotational speed times its diameter 9 What are the 2 most common devices used to vary the capacity of a centrifugal compressor Questions for Period 4 10 Explain why proper water treatment is important Questions for Period 5 11 The refrigerant migration method of free cooling works because refrigerant migrates from the area of temperature to the area of temperature 12 What is the purpose of a fouling factor TRG TRCO10 EN 53 TRANE Answers 1 2 3 4 5 6 7 3 9 kinetic energy to static energy impeller By flashing a portion o
42. onomizer Here the vapor is separated from the mixture and routed directly to the second stage impeller inlet and the remaining liquid travels on to the second expansion device Just before it enters the evaporator the liquid refrigerant flows through a second expansion device that reduces its pressure Pe and temperature to evaporator conditions The cool low pressure mixture of liquid and vapor enters the distribution system in the evaporator shell and absorbs heat from water that flows through the tubes This transfer of heat boils the liquid refrigerant and the resulting saturated refrigerant vapor is drawn back to the compressor to repeat the cycle 17 TRANE 18 period two Refrigeration Cycle 2 stage centrifugal chiller Refrigeration Cycle 2 stage compressor 5 i devices P evaporator A B enthalpy The change in enthalpy from C to A that occurs during the refrigeration cycle is called the refrigeration effect This is the amount of heat that each pound kg of liquid refrigerant will absorb when it evaporates The benefit of the economizer can be demonstrated by comparing the refrigeration cycles with and without an economizer Without an economizer refrigerant from the condenser expands directly to evaporator conditions producing a smaller refrigeration effect B to A Some chiller designs may subcool the liquid refrigerant in the condenser moves to the l
43. ontrol panel and oil pump Every electrically driven chiller requires a starter It must be compatible with the characteristics of both the compressor motor and the electrical circuitry of the chiller There are many types of starters including star delta across the line auto transformer primary reactor and solid state A variable speed drive which is used to modulate the speed of the motor during normal operation also serves as a starter Important characteristics to consider when selecting a starter include first cost reliability line voltage and available current Starters line power line power control power wiring unit mounted control power wiring remote mounted The starter may be mounted on or remotely from the chiller Use of a unit mounted starter reduces electrical installation costs It may also improve reliability and save system design time since all of the components are pre engineered and factory mounted Depending on the type of starter selected there are several options that can simplify installation Disconnects allow the starter to be isolated from the electrical distribution system and short circuit protection can be provided using fuses or a circuit breaker TRG TRC010 EN S TRANE period two Refrigeration Cycle Centrifugal Water Chillers period two Refrigeration Cycle A pressure enthalpy p h chart illustrates the refrigeration cycle of the centrifugal water chiller
44. plication of centrifugal water chillers These included condensing temperature control for water cooled chillers constant or variable evaporator water flow short evaporator water loops heat recovery free cooling and equipment certification standards TRG TRC010 EN period six Review S FRAME An American Standard Company For more information refer to the following references Trane product catalogs for centrifugal water chiller products Trane literature order numbers CTV DS 1 and CTV DS 2 Condensing Water Temperature Control CTV EB 84 Multiple Chiller System Design and Control CON AM 21 Principles of Centrifugal Chiller Heat Recovery Operation AM REF 2 ARI Standard 550 590 1998 Implications For Chilled Water Plant Design Trane Engineers Newsletter 1999 volume 28 no 1 Variable Primary Flow Systems Trane Engineers Newsletter 1999 volume 28 no 3 Chilled Water Systems Engineered Systems Clinics CWS CLC 1 2 3 and 4 ASHRAE Handbook Refrigeration ASHRAE Handbook Systems and Equipment Visit the ASHRAE Bookstore at www ashrae org For information on additional educational materials available from Trane contact your local Trane sales office request a copy of the Educational Materials price sheet Trane order no EM ADV 1 or visit our online bookstore at www trane com bookstore TRG TRCO10 EN 51 S TRANE 52 Quiz Questions for Period 1 1 A centrifugal compressor co
45. ranted variable evaporator water flow Limitations 4 Maintain minimum and maximum water flow rates through the chiller evaporator a Rate at which the evaporator water flow changes must be kept below the corresponding limit to Maintain the chilled water set point control Keep the chiller on line Protect the chiller from damage The controls on many current chiller designs can properly control the chiller in response to varying evaporator flow rates with the following limitations TRG TRCO10 EN 39 mane 40 period five Application Considerations 1 The water flow rate through the chiller evaporator must stay between the minimum and maximum flow rates for the evaporator bundle as specified by the chiller manufacturer These limits depend on the specific design variables of the actual evaporator bundle such as the number of tubes number of passes and geometry Implementation of a method for sensing evaporator water flow through each chiller is the only way to make sure that the water flow rate stays within these limits 2 The rate of change for the evaporator water flow rate must not exceed a specified level depending on the level of protection desired For example the maximum rate of change to maintain the chilled water set point is more stringent than the maximum rate of change to keep the chiller on line There are 3 common levels of protection desired maintaining chilled water set point control keeping the
46. s no additional controls and actually improves chiller efficiency A heat pump chiller is a standard chiller no extra shells are required applied where the useful heat transfer occurs in the condenser not the evaporator The evaporator is connected to the chilled water loop typically upstream of other chillers but it only removes enough heat from the chilled water loop to handle the heating load served by the condenser water loop This application is useful in a multiple chiller installation where there is a base or year round comfort or process load or where the quantity of heat required is significantly less than the cooling load Chiller efficiency is not compromised TRG TRCO10 EN 43 Tane period five Application Considerations Free Cooling air side strainer plate and frame economizer cycle heat exchanger Most efficient Coldest water Potential fouling Requires larger temperatures limited to heat outdoor air e Potential fouling amp XChanger return and in chilled water Requires additional exhaust duct loop heat exchanger systems Requires piping valves and additional piping controls valves and Can operate controls simultaneously with chiller Free Cooling Many buildings require some form of year round cooling to handle interior spaces or other loads When the outdoor air temperature falls below the indoor dew point temperature it is possible to use an air side economizer to satisfy these cooling requir
47. ssages inside the centrifugal compressor that start out small and become larger as the refrigerant travels through them As the size of the diffuser passages increases the velocity and therefore the kinetic energy of the refrigerant decreases This kinetic energy is converted to static energy or static pressure direct drive motor A type of motor that is connected directly to the compressor shaft in which the impeller rotates at the same speed as the motor direct expansion DX shell and tube evaporator A type of evaporator where refrigerant flows through the tubes and water fills the surrounding shell dynamic compression A method of compression that involves converting energy from one form to another to increase the pressure and temperature of the refrigerant vapor 55 TRANE 56 Glossary economizer The component of a multistage centrifugal chiller used to remove vapor from the refrigerant mixture after it passes through an expansion device This reduces the compressor power required since the refrigerant vapor generated in the economizer only needs to be compressed by the higher stage impeller s enthalpy The property of a refrigerant indicating its heat content both sensible and latent evaporator The region of the chiller where the system chilled water is continuously cooled by boiling the refrigerant as it picks up heat from the returning system water expansion device The component of the chiller used to redu
48. ssages into the impeller This instantaneously reduces the pressure within the passages below the radial force and the compressor is able to re establish the proper direction of refrigerant flow This condition is known as surge So long as this unstable load condition exists the refrigerant alternately flows backward and forward through the compressor impeller generating noise and vibration Compressor Map oe eosensee anen SSN i STACK i 51 63 36 T 10 44 25 vane position degrees refrigerant flow rate These curves represent the performance of a typical 2 stage compressor over a range of inlet vane positions The pressure difference between the compressor inlet evaporator and outlet condenser is on the vertical axis and the refrigerant flow rate is on the horizontal axis The dashed line represents the TRG TRCO10 EN TRG TRCO10 EN S TRANE period three Compressor Capacity Control conditions that cause the compressor to surge Any operating point that falls to the right of this line is satisfactory for stable operation Operating Point operating point pressure difference refrigerant flow rate To balance the load on the chiller the compressor must pump a certain quantity of refrigerant vapor at evaporator pressure and elevate it to the pressure dictated by the condensing conditions The intersection of the refrigerant flow rate and the pressure difference between the inlet and outlet of the compre
49. ssor identifies the compressor operating point compressor map for a 2 Stage Compressor ION 14 25 vane position degrees refrigerant flow rate Superimposing the operating point on the previous compressor performance curves establishes the point at which the compressor will balance the load In this example the compressor will balance the load with its inlet vanes open 90 27 S TRANE period three Compressor Capacity Control compressor map for a 2 Stage Compressor A n 90 unloading line refrigerant flow rate The starting point A is the full load operating point As the load on the chiller decreases the inlet vanes partially close reducing the flow rate of refrigerant vapor through the compressor and balancing the chiller capacity with the new load B Less refrigerant and therefore less heat is transferred to the condenser Since the heat rejection capacity of the condenser is now greater than required the refrigerant condenses at a lower temperature and pressure This reduces the pressure difference between the evaporator and the condenser Continuing along the unloading line the compressor remains within its stable operating range until it reaches the surge region at 28 TRG TRC010 EN S TRANE period three Compressor Capacity Control Adjustable Frequency Drives inlet vanes only AFD inlet vanes power consunption load An adjustable frequency drive A
50. stems are designed They are not suggestions for good design practice for a TRG TRCO10 EN TRG TRCO10 EN S TRANE period five Application Considerations given system they simply define a common rating point to aid comparisons Trends toward improved humidity control and energy efficiency have changed some of the actual conditions selected for specific applications Impurities in the chilled and condenser water systems eventually deposit on evaporator and condenser tube surfaces impeding heat transfer Catalogued performance data includes a fouling factor that accounts for this effect to more closely predict actual chiller performance ARI s part load efficiency rating system establishes a single blended estimate of stand alone chiller performance The Integrated Part Load Value IPLV predicts chiller efficiency at the ARI standard rating conditions using weighted averages representing a broad range of geographic locations building types and operating hour scenarios both with and without an air side economizer While the weighted averages place greater emphasis on the part load operation of an average single chiller installation they will not by definition represent any particular installation Additionally ARI notes that more than 80 percent of all chillers are installed in multiple chiller plants Chillers in these plants exhibit different unloading characteristics than the IPLV weighted formula indicates Appendix D o
51. ts for other centrifugal chiller designs are also included Maintenance Considerations a Operating log a Mechanical components a Heat transfer surfaces a Fluid analysis Once a centrifugal chiller is installed and put into operation it usually continues to function without a full time attendant In many cases the machine starts and stops on a schedule controlled by a building automation system or a simple time clock The only daily maintenance requirement is to complete and review the operating log Water chillers are designed for maximum reliability with a minimum amount of maintenance Like all large mechanical systems however certain routine maintenance procedures are either required or recommended 30 TRG TRCO10 EN TRG TRCO10 EN period four Maintenance Considerations S TRANE operating log ASHRAE Guideline 3 A a Chilled water flow a Evaporator refrigerant Chilled water inlet and outlet A temperatures and pressures temperature and pressures Evaporator approach temperature Condenser water inlet and outlet temperatures and pressures Condenser water flow a Condenser refrigerant temperature and pressures Condenser approach temperature Oil pressures temperature and levels a Addition of refrigerant a Addition of oil a Vibration levels Guideline 3 Reducing Emission of Halogenated Refrigerants in Refrigeration and Air Conditioning Equipment and Systems is one of several adv
52. ular oil analyses can be used to determine proper oil change intervals and predict major problems before they occur Refrigerant analysis measures contamination levels and determines suitability for continued use It can also determine if recycled refrigerant is suitable for reuse Refrigerant analysis helps extend the life of the existing charge and ensures that the chiller is operating at peak efficiency TRG TRCO10 EN TRG TRCO10 EN S TRANE period four Maintenance Considerations Regularly logging oil and refrigerant charges and examining the trends of this data can help identify potential problems before they occur Oil Analysis a Why perform regular oil analysis Helps reduce maintenance costs Detects problems without compressor disassembly Extends service life of oil charge Reduces environmental problems related to oil disposal Helps maintain compressor efficiency and reliability Helps lower refrigerant emissions An oil analysis is a key preventive maintenance measure and should be conducted at least annually It will help the compressor last longer while maintaining chiller efficiency and reducing refrigerant emissions A certified chemical laboratory can be contracted to perform the analysis for all types of compressors Often the chiller manufacturer can provide this service 35 S TRANE 36 period five Application Considerations Centrifugal Water Chillers period fi
53. ulating a throttling valve to restrict the flow of water through the condenser 4 Using a chiller bypass pipe to vary the flow rate of water through the condenser 5 Using a variable speed drive on the condenser water pump to vary the water flow rate through the condenser Each of these strategies has its advantages and disadvantages Selecting the appropriate condensing temperature control scheme will depend on the specific requirements of the application The water flow rate through the chiller condenser must stay between the minimum and maximum condenser bundle flow rates specified by the chiller manufacturer 38 TRG TRCO10 EN S TRANE period five Application Considerations evaporator water flow Constant or Variable Flow chilled water pump evaporator E variable speed drive Constant or Variable Evaporator Water Flow Previous chiller designs required that a constant flow rate of water be maintained through the evaporator This requirement has changed due to advances in chiller controls Increased sensing and control capabilities now allow chiller manufacturers to design controls that monitor and respond faster to fluctuating conditions While the chiller may be able to handle variable water flow through the evaporator the specific application of the chilled water system may not warrant variable flow As always each application should be analyzed to determine if variable evaporator water flow is war
54. ve Application Considerations Several considerations must be addressed when applying centrifugal water chillers including Condensing temperature control Constant or variable evaporator water flow Short evaporator water loops Heat recovery Free cooling Equipment certification standards While not all inclusive this list of considerations does represent some of the key issues TRG TRC010 EN S TRANE period five Application Considerations Condensing Temperature Control vane position degrees unloading line refrigerant flow rate Condensing Temperature Control To achieve stable compressor unloading over a wide range of conditions a reduction in condensing pressure condenser relief must accompany a reduction in load The starting point A is the full load operating point As the chiller load decreases the flow rate of refrigerant vapor through the compressor also decreases In turn the pressure difference between the evaporator and the condenser moves the operating point downward toward B If the condenser pressure had been controlled to a constant value instead the compressor would have unloaded along a nearly constant pressure line toward C This would result in a greatly reduced range of operation Condenser relief is however only beneficial to a certain point ALL chillers require a minimum pressure difference between the evaporator and condenser to ensure proper management of oil and refrigera
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