Trane trg-trc005-en User's Manual
Contents
1. replaceable core typ gt sealed type A typical liquid line filter drier includes a molded porous core The core has a high affinity for moisture and removes foreign matter from the refrigerant The two common types of filter driers are replaceable core and sealed The replaceable core type allows the core to be easily replaced The sealed type is completely closed reducing the chances of refrigerant leaks Ball type shutoff valves are typically installed just upstream and downstream to allow the filter drier to be isolated and the core or unit replaced 37 S TRANE 38 period five Accessories Moisture Indicating Sight Glass liquid line sd lll mm Moisture Indicating Sight Glass A moisture indicating sight glass is installed in the liduid line upstream of the expansion valve and permits the operator to observe the condition of the refrigerant prior to entering the expansion valve The value of the sight glass is in its moisture indication ability the sight glass should not be used to determine system refrigerant charge or subcooling Actual temperature and pressure measurements are required to determine proper charge and subcooling With the sight glass installed directly ahead of the expansion valve it can also be used to detect the presence of bubbles in the liquid line This would indicate that some of the liquid refrigerant has flashed into vapor upstream of the expansion valve Since the2. Air Conditioning Clinic Refrigeration System Components One of the Fundamental Series TRG TRC005 EN abpe WO GLO UONEIOLSd doV WOROA WO G G UONEIOHEJ a 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 Refrigeration System Components Level of detail circle one Too basic Just right Too difficult One of the Fundamental Series Rate this clinic from 1 Needs Improvement to 10 Excellent TRG TRCOOS EN Content 1 2 3 4 5 6 7 8 9 10 Booklet usefulness 1 2 3 4 5 6 7 8 9 10 Slides illustrations 1 2 4 5 6 7 8 3 10 Presenter s ability 1 2 3 4 5 6 7 8 9 10 Training environment 1 2 4 5 6 7 8 9 10 Other comments About me Type of business Job function Optional name phone address Give the completed card to the presenter or drop it in the mall Thank you TRANE The Trane Company Worldwide Applied Systems Group 3600 Pammel Creek Road La Crosse WI 54601 7599 www trane com An American Standard Company Response 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 J Air Conditioning C
3. Turbulent Flow The fins of the coil are formed to produce turbulence as the air passes through them This turbulence enhances heat transfer preventing stratification within the coil leaving airstream Finned Tube Evaporator liquid vapor refrigerant airflow liquid distributor WE s suction v refrigerant vapor header 9 p To provide uniform heat transfer throughout the coil the liquid refrigerant is distributed to the coil tubes in several parallel circuits A distributor is used to ensure uniform refrigerant distribution through these multiple coil circuits It distributes the liquid vapor refrigerant mixture to the coil through several tubes of equal length and diameter As the refrigerant passes through the tubes of the coil the liquid refrigerant absorbs heat from the air causing it to boil off into vapor The refrigerant vapor leaves the coil tubes and collects in a suction header 17 18 period three Evaporators Each distributor has an allowable range of refrigerant flow rates that define its stable operating range As the size of the evaporator coil increases it may be necessary to use more than one distributor to feed liquid refrigerant to the coil Superheat superheat Inside the final length of tubes he location where the temperature difference between the refrigerant and the air is highest 4his larger temperature difference accelerates the rate of heat transfer and the refrigeran
4. filter drier evaporator compressor shutoff valves Shutoff Valve Shutoff valves are used to isolate one part of the refrigeration system from the rest Additionally they can be used to trap the refrigerant charge in one component of the system the condenser for example to permit service or repair to another part of the system Common uses of shutoff valves include m Isolating the liquid line filter drier and suction filter to allow easier core or unit replacement m Isolating the compressor from the rest of the system to allow for repair or replacement m Isolating the charge within the condenser or a receiver to allow access to the rest of the system TRG TRCOOS EN 41 42 period five Accessories Access Port condenser liquid line access port ZI gt compressor suction line access ports Access Port An access port is used to add refrigerant to the system or for measurement An access port is typically installed in the liquid line in a convenient location and is used to charge the system with liquid refrigerant It is also used to measure subcooling The suction line typically includes two access ports One is installed near the compressor and is used to measure suction pressure The other is located near the external equalizer line connection for the expansion valve and is used to measure superheat when checking or adjusting the expansion valve setting TRG TRC005 EN TRG
5. moving the point of complete vaporization toward C The resulting reduction in superheat creates a lower pressure inside the remote bulb and therefore on the top side of the diaphragm This causes the valve to close more reducing the flow of liquid refrigerant into the evaporator This reduction in refrigerant flow moves the point of complete vaporization back toward A reestablishing the desired superheat condition 32 TRG TRCOOS EN TRG TRCOOS EN TRANE period Tour Expansion Devices Superheat Setting Too little superheat Risk of damage to compressor by liquid refrigerant Too much superheat Reduction of system efficiency Potential of coil frosting Risk of compressor damage due to overheating A typical recommended superheat setting is from 8 to 12 F 4 4 to 6 7 C Too little superheat is risky because it presents a danger of allowing refrigerant to leave the evaporator in the liquid state As mentioned earlier the compressor is designed to compress vapor not liquid Liquid refrigerant can cause damage to the compressor Too much superheat dedicates too much of the tube surface to the production of superheat reducing system efficiency In extreme cases it can lead to coil frosting it may also cause the compressor to overheat possibly shortening its service life 33 period Tive Accessories Refrigeration System Components period five Accessories This period discusses several
6. 11 Too much superheat dedicates too much of the tube surface to the production of superheat reducing system efficiency In extreme cases it can lead to coil frosting and overheating of the compressor compromising its longevity 12 Low pressure side to the high pressure side 13 Upstream of the expansion valve TRG TRCOOS EN TRG TRCOOS EN S TRANE Glossary access port A device that allows a technician to gain access to the refrigeration system for charging or measurement air cooled condenser A type of condenser where refrigerant flows through the tubes and rejects heat to air that is drawn across the tubes ASHRAE American Society of Heating Refrigerating and Air Conditioning Engineers capillary tube A type of expansion device that uses a long narrow tube to reduce the pressure and temperature of the refrigerant centrifugal fan air cooled condenser A type of air cooled condenser that uses a centrifugal fan instead of a propeller fan allowing it to overcome the larger static pressures associated with ductwork compressor The mechanical device in the refrigeration system used to increase the pressure and temperature of the refrigerant vapor condenser The component of the refrigeration system where refrigerant vapor is converted to liquid as it rejects heat to water or air cooling tower A device used to reject the heat from a water cooled condenser by spraying the condensing water over the fill while drawing ou
7. It ensures that the refrigerant will be completely vaporized within the evaporator and maintains the proper amount of superheat in the system 45 46 period six Review Review Period Five shutoff access port condenser suction line filter liquid line glass filter drier evaporator Period Five discussed several accessories commonly used in comfort cooling applications including solenoid valve liquid line filter drier moisture indicating sight glass suction line filter hot gas muffler shutoff valve and access port The solenoid valve is used to stop the flow of refrigerant within the system A liquid line filter drier prevents moisture and foreign matter from damaging the valves or compressor The moisture indicating sight glass permits the operator to observe the condition of the refrigerant within the liquid line before it enters the expansion device A suction line filter protects the compressor from foreign matter in the suction line The hot gas muffler is used to reduce noise and vibration associated with reciprocating compressors Shutoff valves are used to isolate one part of the refrigeration system and access ports allow a technician to gain access to the system for charging or measurement TRG TRCOOS EN period six Review TRANE An American Standard EEN id For more information refer to the following references Trane Air Conditioning Manu
8. TRCOOS EN period six Review Refrigeration System Components period six Review We will now review the main concepts that were covered in this clinic about the components in a vapor compression refrigeration system Review Period One condenser evaporator expansion device pressure compressor A enthalpy Period One reviewed the vapor compression refrigeration cycle using the P h chart A cool low pressure mixture of liquid and vapor refrigerant enters the evaporator A and absorbs heat from the relatively warm air or water that is being cooled This transfer of heat boils the liquid refrigerant in the evaporator and superheated refrigerant vapor B is drawn to the compressor The compressor raises the pressure and temperature C high enough that the refrigerant vapor can reject heat to another fluid This hot high pressure refrigerant vapor then travels to the condenser where heat is transferred to relatively cool ambient air or cooling water This reduction in the heat content 43 44 period six Review of the refrigerant vapor causes it to desuperheat condense into liquid and further subcool before leaving the condenser D for the expansion device Finally the high pressure liquid refrigerant flows through the expansion device causing a large pressure drop the line from D to A that reduces the pressure of the refrigerant to that of the evaporator This pressure reduction c
9. accessories used in comfort cooling refrigeration systems Solenoid Valve Solenoid Valve A solenoid valve is used to stop the flow of refrigerant within the system These valves are magnetically operated and an electric winding controls the opening and closing of the valve The valve is typically a normally closed type of valve so that it is closed when it is deenergized 34 TRG TRCOOS EN TRG TRCOOS EN period five Accessories Solenoid Valve d expansion finned tube evaporator solenoid valves One common use of a solenoid valve is to control the flow of liquid refrigerant to multiple sections of the evaporator In this application a valve is installed in the liquid line upstream of the expansion valve for each individually controlled section of the evaporator coil Using the example of a face split evaporator coil at lower loads a solenoid valve may be used to shut off the flow of liquid refrigerant to the top section of the coil A portion of the air passes through the active lower section and is cooled while the rest of the air passes through the inactive top section and remains unconditioned The two airstreams mix downstream of the coil At higher loads both sections of the coil are activated Solenoid Valve liquid line discharge line condenser expansion compressor valve evaporator suction line solenoid valve Another common use of a sole
10. expansion valve is designed to control the flow of liquid refrigerant only the presence of refrigerant vapor results in a reduction in the quantity of liquid refrigerant being fed to the evaporator There are many potential causes of liquid refrigerant flashing The sight glass can alert the operator to the condition TRG TRCOOS EN TRG TRCOOS EN period five Accessories Suction Line Filter compressor suction line Suction Line Filter Similar to the liquid line filter drier the suction line filter performs the task of removing foreign matter from the refrigeration system It is installed in the suction line just upstream of the compressor The suction filter contains filter media to remove copper filings flux dirt and other foreign matter that may have been introduced during the installation process or as the result of acompressor failure It protects the compressor parts from the abrasive action that could result if these materials enter the compressor Dirt can obstruct oil passages robbing the compressor bearings of lubrication Suction Line Filter replaceable core type Similar to the liquid line filter drier the two common types of suction line filters are replaceable core and sealed The replaceable core type allows the core to be easily replaced The sealed type is completely closed reducing the chances of refrigerant leaks 39 period five Accessories Replaceable core suction fi
11. has flooded enough that its capacity is reduced to the point where the condensing pressure rises above the pressure in the receiver the higher pressure condensed liquid will flow through check valve C into the receiver This increases the pressure in the receiver above the minimum condensing pressure set point closing valve A Condenser coil flooding provides the capacity modulation range needed to produce acceptable condensing pressures at reduced loads and correspondingly low outdoor temperatures 15 16 period three Evaporators Refrigeration System Components period three Evaporators The second major component to be discussed is the evaporator The evaporator is a heat exchanger that transfers heat from air water or some other fluid to the cool liquid refrigerant Two common types of evaporators are the finned tube and the shell and tube Finned Tube Evaporator liquid vapor refrigerant We airflow E refrigerant vapor P Finned Tube Evaporators A finned tube evaporator includes rows of tubes passing through sheets of formed fins Cool liquid refrigerant flows through the tubes cooling the tube and fin surfaces As air passes through the coil and comes into contact with the cold fin surfaces heat is transferred from the air to the refrigerant This heat transfer causes the refrigerant to boil and leave the evaporator as vapor TRG TRC005 EN TRG TRCOOS EN period three Evaporators
12. heat transfer surface inside a cooling tower finned tube evaporator A type of evaporator where refrigerant flows through the tubes and air blows across the tubes and fins flash The process of liquid refrigerant being vaporized by a sudden reduction of pressure hot gas muffler A device installed at the discharge of the compressor to reduce noise and vibration associated with reciprocating compressors intertwined A type of finned tube evaporator arrangement that splits the coil by alternating the tubes fed in each row between two distributors liquid line filter drier A device installed in the liquid line to remove moisture water and foreign matter introduced during the installation process from the refrigeration system moisture indicating sight glass See sight glass moisture indicating 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 pressure enthalpy chart A graphical representation of the saturated properties of a refrigerant plotting refrigerant pressure versus enthalpy pump down cycle A control sequence used in a refrigeration system to pump the refrigerant from the low pressure side of the system to the high pressure side of the system refrigeration effect The amount of heat that each pound kg of liquid refrigerant will absorb when it evaporates row split A type of finned tube evaporator arrangement that splits
13. refrigerant The cycle starts with a cool low pressure mixture of liquid and vapor refrigerant entering the evaporator A where it absorbs heat from the relatively warm air water or other fluid that is being cooled This transfer of heat boils the liquid refrigerant in the evaporator and this superheated refrigerant vapor is drawn to the compressor B TRG TRCOOS EN TRANE period one Refrigeration Cycle Refrigeration Cycle OO compressor pressure A evaporator enthalpy The compressor draws in the superheated refrigerant vapor B and compresses it to a pressure and temperature C high enough that it can reject heat to another fluid This hot high pressure refrigerant vapor then travels to the condenser Refrigeration Cycle pressure A evaporator enthalpy Within the condenser heat is transferred from the hot refrigerant vapor to relatively cool ambient air or cooling water This reduction in the heat content of the refrigerant vapor causes it to desuperheat condense into liquid and further subcool before leaving the condenser D for the expansion device TRG TRCOOS EN 3 S TRANE period one Refrigeration Cycle Refrigeration Cycle condenser D C D expansion D device compressor Q A evaporator enthalpy Finally the high pressure liquid refrigerant D flows through the expansion device causing a large pressure drop that reduces the pressure
14. the coil by placing the independently controlled coil sections in series in the airstream shell and tube evaporator A type of evaporator where refrigerant flows through the tubes and water fills the surrounding shell shutoff valve Devices used to isolate one part of the refrigeration system from the rest sight glass moisture indicating A device installed in the liquid line upstream of the expansion valve used to detect moisture in the system and determine if the liquid refrigerant has flashed into vapor before entering the expansion valve solenoid valve A device used to stop the flow of refrigerant within the refrigeration system TRG TRCOOS EN TRG TRCOOS EN S TRANE Glossary subcooler The lower portion of the condenser that further cools the saturated liquid refrigerant suction header A section of pipe used to collect the refrigerant vapor when it leaves the tubes of a finned tube evaporator coil suction line filter A device installed in the suction line to remove foreign matter from the refrigeration system superheat The amount of heat added to the refrigerant vapor after it has completely vaporized within the evaporator thermostatic expansion valve A type of expansion device that uses a thermally actuated valve to sense and control the flow rate of liquid refrigerant to the evaporator water cooled condenser A type of condenser where water flows through the tubes and absorbs heat from the refrigerant
15. three Evaporators The face split coil configuration also called horizontal split or parallel flow is split into parallel sections A portion of the air passes through the top section the remainder passes through the bottom section and the two airstreams mix downstream of the coil Face Split Arrangement 80 F 27 C At lower loads only one section of the face split coil is active A portion of the air passes through the active lower section and is cooled while the rest of the air passes through the Inactive top section and remains unconditioned The two airstreams mix downstream of the coil producing average temperature and humidity conditions At higher loads both sections of the coil are activated providing a more uniform leaving air temperature In a VAV application where the leaving air is controlled to a constant temperature the active section of coil must supply colder air than the desired average temperature at part load Consequently the refrigerant must get colder at part load eventually reaching a condition where the coil surface is cold enough that the water condensing from the air will create frost on the coil Resetting the supply air temperature upward can help to avoid this problem but this may result in soace humidity problems In constant volume applications where the leaving air temperature varies to respond to changing loads this is not as much of a concern since the average mixed temperature ri
16. able spring that applies a force to the lower side of the diaphragm TRG TRCOOS EN S TRANE period Tour Expansion Devices TXV Operation valve diaphragm 97 psia 0 67 MPa 79 psia 18 psi 0 54 MPa 0 13 MPa suction line valve pin Using the conditions from the previous example the 49 F 9 4 C refrigerant vapor leaving the evaporator boils the refrigerant in the bulb generating 97 psia 0 67 MPa of pressure within the remote bulb This pressure is transmitted to the top side of the valve diaphragm creating a force that pushes down on the diaphragm The 79 psia 0 54 MPa evaporating pressure on the other hand is transmitted to the bottom side of the valve diaphragm producing an opposing force Since the difference between the evaporator pressure and the pressure within the remote bulb is due to superheat the tension of the spring is adjusted to provide the difference in order to balance the forces and produce the desired amount of superheat In this example the spring tension is adjusted to produce an 18 psi 0 13 MPa pressure difference which corresponds to 12 F 6 7 C of superheat Any variation in evaporator pressure causes these forces to vary from this equilibrium and move the pin up or down thus closing or opening the valve Closing the valve reduces the flow of refrigerant to the evaporator while opening the valve increases the flow In other words with this valve spring
17. adjustment the refrigerant vapor must absorb 12 F 6 7 C of superheat before the forces that open and close the valve come into equilibrium stabilizing the refrigerant flow rate to the evaporator TRG TRCOOS EN 31 S TRANE period four Expansion Devices TXV Operation external equalizer m p a N ON O a _ ed N Ed ed O O ar N O U ie u ae Bot a i i bE AM aE bE eS Si uE ee AA uE EA HE ee ee oa i AA Aa ee a N EEUE EE EEEEEEE EE EE HEER E EE p ea Es E BE RES LE RE ESE RE RE AA N SS ee ee ee eee ee N ee TE i remote bulb For example assume that an increasing system load causes the refrigerant within the coil to vaporize at a faster rate than desired This moves the point at which the refrigerant becomes completely vaporized from A toward B This increase in coil surface used for superheating results in the refrigerant vapor leaving the evaporator at a higher temperature Sensing the rising superheat the remote bulb transmits a higher pressure to the top side of the TXV diaphragm causing the valve to open further and allow more refrigerant to flow into the evaporator This increased flow of refrigerant moves the point of complete vaporization back toward A until the desired superheat condition is reestablished and the opening and closing forces within the valve equalize at a refrigerant flow rate that balances the new system load Conversely a decreasing system load slows the rate at which the refrigerant vaporizes
18. al Trane Reciprocating Refrigeration Manual The DX Refrigerant Cooling Coil Conundrum Trane Engineers Newsletter 1988 volume 17 number 1 ASHRAE Handbook Fundamentals ASHRAE Handbook Refrigeration ASHRAE Handbook Systems and Equipment Visit the ASHRAE Bookstore at www ashrae org For more information on additional educational materials available from Trane contact your local Trane office request a copy of the Educational Materials catalog Trane order number EM ADV1 or visit our online bookstore at www trane com bookstore TRG TRCOOS EN 47 48 Quiz Questions for Period 1 pressure enthalpy Using the pressure enthalpy chart in Figure 68 which two points correspond to superheating the refrigerant vapor inside the evaporator Again using Figure 68 which two points correspond to subcooling the liquid refrigerant inside the condenser Questions for Period 2 List the three common types of condensers What two factors cause the condensing pressure to drop What are two methods of control that can be applied to air cooled condensers Questions for Period 3 6 What is the name of the device used to ensure uniform refrigerant distribution through the multiple coil circuits of a finned tube evaporator What is the purpose of the baffles inside the shell and tube evaporator What are the three common arrangements for splitting finned tube evaporator coils When using a face split c
19. aporating temperature The 12 F 6 7 C temperature difference between this evaporating temperature and the temperature measured at the outlet of the evaporator is the amount of additional heat or superheat absorbed by the refrigerant vapor in the final lengths of coil tubing Notice that superheating the refrigerant vapor changed only its temperature not its pressure These same properties the evaporator pressure and the final refrigerant vapor temperature are measured and used by the thermostatic expansion valve to control the quantity of liquid refrigerant entering the evaporator TRG TRCOOS EN 29 30 period four Expansion Devices TXV Operation remote suction xternal lizer ling external equalize distributor In a typical TXV application the outlet of the valve is connected to the distributor A remote bulb is attached to the suction line where it senses the refrigerant vapor temperature leaving the evaporator This bulb is charged with refrigerant and as heat is transferred from the suction line to the bulb the refrigerant inside the bulb vaporizes The resulting refrigerant vapor pressure is transmitted through a tube to the space above a diaphragm in the TXV The pressure of the refrigerant vapor leaving the evaporator is transmitted to the space beneath the diaphragm through an external equalizing line that is tapped into the suction line downstream of the bulb Finally the valve contains an adjust
20. auses a small portion of the liquid to boil off or flash cooling the remaining refrigerant to the desired evaporator temperature The cooled refrigerant then enters the evaporator A to repeat the cycle Review Period Two evaporative dh condenser air cooled condenser water cooled condenser Period Two discussed the different types of condensers and methods of condenser control The condenser rejects heat from the refrigerant to air water or some other fluid The three common types of condensers are air cooled water cooled and evaporative TRG TRC005 EN TRG TRCOOS EN period six Review Review Period Three finned tube evaporator shell and tube evaporator Period Three presented the different types of evaporators and methods of evaporator control The evaporator transfers heat from air water or some other fluid to the cool liquid refrigerant The two common types of evaporators are finned tube and shell and tube Review Period Four distributor p external equalizer Period Four reviewed the operation of the expansion device specifically the thermostatic expansion valve The expansion device is used to maintain the pressure difference between the high pressure condenser and low pressure evaporator sides of the system established by the compressor In addition the thermostatic expansion valve TXV controls the quantity of liquid refrigerant entering the evaporator
21. e same time the outdoor air temperatures has fallen to the point where the rate of heat rejection from the condenser balances the load at a condensing pressure less than desired This minimum condensing pressure is the set point for valve A As the condensing pressure decreases so does the pressure in the discharge line Valve B acts as a pressure regulator and when the discharge line pressure falls below its set point valve B closes This causes the condensing pressure to drop farther Sensing this reduction in condensing pressure valve A opens and directs hot high pressure refrigerant vapor into the receiver This increases the pressure in the receiver controlling It to the desired condensing pressure Because the pressure in the receiver is now higher than the pressure in the condenser the check valve C does not allow the refrigerant to flow back into the condenser With valve B closed and valve A modulating to maintain the pressure in the receiver the pressure in the discharge line begins to increase When it exceeds the set point for valve B the valve opens and again allows hot refrigerant vapor into the condenser However since the condensing pressure is still below the pressure in the receiver the refrigerant cannot flow through valve C This causes the condensed liquid to remain in the condenser where it backs up or floods the condenser tubes The flooding of tubes causes the condenser to progressively lose capacity When it
22. ed liquid b refrigerant Water Cooled Condensers The shell and tube is the most common type of water cooled condenser With this design water is pumped through the tubes while the refrigerant vapor fills the shell space surrounding the tubes As heat is transferred from the refrigerant to the water the refrigerant vapor condenses on the tube surfaces The condensed liquid refrigerant then falls to the bottom of the shell where it flows through an enclosure that contains additional tubes the subcooler More heat is transferred from the liquid refrigerant to the water inside these tubes subcooling the refrigerant After the warm water leaves the condenser it must either be disposed of as in the case of using water from a well or it must be cooled before it can be reused by the condenser In this example the condenser brings in 85 F 29 C water and warms it up to 95 F 35 C Before this water can be used again it must be cooled back down to 85 F 29 C TRG TRC005 EN TRG TRCOOS EN period two Condensers Cooling Tower propeller fan sprays fill Outdoor alr 8 95 F 35 C condenser condenser A cooling tower is a device commonly used to cool condensing water In this design warm water is sprayed over the fill inside the cooling tower while a propeller fan draws outdoor air upward through the fill The movement of air through the spray causes some of the water to evaporate a process that c
23. emperatures S TRANE 10 period two Condensers Condenser Control Condenser capacity is influenced by Temperature difference between refrigerant and cooling media Flow rate of cooling media through condenser Flow rate of refrigerant through condenser Condenser Control The heat rejection capacity of a condenser is influenced by 1 the temperature difference between the refrigerant and the cooling media air water or other fluid 2 the flow rate of the cooling media through the condenser and 3 the flow rate of the refrigerant through the condenser To balance the rate of heat rejection in the condenser with the changing system load at least one of these variables may be controlled Condenser Capacity full load condenser heat fullload N miei ele ae HE B part load part load c condenser heat rejection capacity enthalpy As the system load decreases the heat rejection capacity of the condenser is greater than the load Because of this excess capacity the condenser matches the decreasing load by operating at progressively lower pressures Additionally a reduction in outdoor air temperature allows the temperature of the air or water flowing through the condenser to drop This also has the effect of lowering the condensing pressure TRG TRCOOS EN TRG TRCOOS EN S TRANE period two Condensers A reduction in condensing pressure lessens the power required to compress
24. erant pressure to that of the evaporator This pressure drop causes a small TRG TRCOOS EN S TRANE period Tour Expansion Devices portion of the liquid to boil off or flash and has the effect of cooling the remaining liquid refrigerant to the desired evaporator temperature The resulting pressure of the refrigerant is 85 psia 0 59 MPa which corresponds to 41 F 5 C Inside the evaporator tubes as heat is transferred to the liquid refrigerant it boils until only vapor remains A From this point the vapor continues to absorb heat as it passes through the final lengths of coil tubing superheating the vapor Superheat 85 psia 41 F 0 59 MPa 5 C BEE BASE E E E BE SEE AT ar LL Lr eg EE EE EEUE EFESE RAN EE EE EENS N ET ttt NE N EE HE MEE EE HE N EE ME N EE EE 290 psia 109 Ri ARE GN N 2 MPa 42 8 C m FT ki dr ee EE aai hadai dai A ia A a d 49 F 9 4 C N Continuing with this example the refrigerant enters the evaporator coil at 85 psia 0 59 MPa and 41 F 5 C Assuming that the pressure drop through the coil tubes is 6 psi 0 04 MPa the refrigerant vapor leaves the coil at 79 psia 0 54 MPa The temperature gauge at the outlet of the evaporator coil indicates that the superheated refrigerant vapor leaves at 49 F 9 4 C A table of refrigerant properties for Refrigerant 22 in this example would show that the 79 psia 0 54 MPa pressure corresponds to a 37 F 2 8 C ev
25. eration effect TRG TRCOOS EN 28 period four Expansion Devices TXV Control ne Ag E EE refrigerant ME p E EE 0 0 p p H AA a a a ea ee el hel hel a a el fe j liquid vapor ay KERE F Tata 7 a TAT a7 aa ee mixture ki rr EE k EEEE a de de le re Jee ETE HEN EE EE HERE FEE EE EE EE HA Eie On the other hand if too much liquid refrigerant enters the evaporator not all of it will be vaporized As a result some liquid refrigerant gets into the compressor suction line Since the compressor is designed to compress vapor and not liquid liquid refrigerant can cause excess wear and damage to the compressor Superheat 85 psia 41 F 0 59 MPa 5 C 8s Peg BT ow TR ATR GEEET liquid refrigerant E 8 amp 290 psia 109 F 2 MPa 42 8 C t superheated vapor The TXV meters refrigerant by measuring the condition of the refrigerant vapor leaving the evaporator Superheat is the additional heat absorbed by the refrigerant in the evaporator after it has completely vaporized It provides a safety factor by preventing liquid refrigerant from entering the compressor In the example above subcooled liquid refrigerant enters the TXV ata condensing pressure of 290 psia 2 MPa and a temperature of 109 F 42 8 C The refrigerant condensed at 124 3 F 51 3 C and was subcooled to 109 F 42 8 C Passing through the TXV causes a large pressure drop reducing the refrig
26. linic series About me LY Engineered Systems Clinic series Name J Trane Air Conditioning Manual Tite 0 J Trane Systems Manual Business type gt gt S SSSss SS o o o Software tools L Equipment Selection Phone fax o S S oS S oo I System design amp analysis E mail address SS Periodicals L Engineers Newsletter Company 2 Other E Address S TRANE The Trane Company Worldwide Applied Systems Group 3600 Pammel Creek Road La Crosse WI 54601 7599 www trane com Thank you for your Interest An American Standard Company 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 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 NO POSTAGE NECESSARY IF MAILED IN THE UNITED STATES NO POSTAGE NECESSARY IF MAILED IN THE UNITED STATES Crop to width of 7 75 Refrigeration System Components One of the Fundamental Series A publication of The Trane Company Worldwide Applied Systems Group Preface Refrigeration System Components A Trane Air Conditioning Clinic The Trane Company believes that it is incumbent on manufacturers to serve the industry by regularly disse
27. loading or cycling compressors To provide stable part load operation and balance compressor unloading with the capacity of the evaporator some direct form of evaporator capacity control may also be required TRG TRCOOS EN TRG TRCOOS EN period three Evaporators Finned Tube Evaporator Control 7 P P GE GE Aa a ee ee oa AT aa il expansion f i valve evaporator m dx T Se EE THVERT EULER YE Ser i q u id em refrigerant a itera 7 2 refrigerant vapor hd a bet ie He Fort ot Typically an expansion valve is used to control the flow rate of refrigerant through the evaporator to maintain the proper amount of superheat ensuring that the liquid refrigerant will be completely vaporized Working in conjunction with the unloading or cycling compressors the expansion valve allows the evaporator capacity to match the system load The operation of the expansion valve will be discussed further in Period Four Face Split Arrangement distributors When an evaporator contains more than one liquid refrigerant distributor it is split into independently controlled sections each being served by its own expansion valve By turning on and shutting off these coil sections the evaporator can further control its capacity to better match the system load The three common arrangements for splitting finned tube evaporator coils include face split intertwined and row split 21 22 period
28. lters are commonly installed after a compressor failure has occurred The core is replaced after the foreign matter or acid has been removed from the system Additionally suction filters should be installed in all field assembled systems Hot Gas Muffler i discharge line reciprocating compressor perforated tube Hot Gas Muffler The purpose of the hot gas muffler is to smooth out the pulsations associated with the refrigerant vapor being discharged from a reciprocating compressor reducing noise and vibration The pressure of the refrigerant vapor leaving a reciprocating compressor fluctuates rapidly because of the manner in which it is compressed by the reciprocating pistons The muffler contains a perforated tube inside a shell The pressure peaks cause some of the refrigerant vapor to pass from the perforated tube into the muffler shell This shell is divided into chambers that allow it to absorb these peaks In essence the muffler shaves off the peaks of these pulsations and fills in the valleys reducing the pulsating characteristic in the discharge line When used the hot gas muffler should be located in the discharge line as close to the reciprocating compressor discharge as possible This minimizes the sound emission from the unmuffled section of discharge line TRG TRCOOS EN period five Accessories Shutoff Valve shutoff valve liquid line condenser liquid line
29. minating information gathered through laboratory research testing programs and field experience The Trane Air Conditioning Clinic series is one means of knowledge sharing It is intended to acquaint a nontechnical audience with various fundamental aspects of heating ventilating and air conditioning We have 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 reader to the concept of vapor compression refrigeration system components 1999 American Standard Inc All rights reserved TRG TRCOOS EN TRG TRCOOS EN Contents period one period two period three period four period five period six Introduction ooo ee ee ee 1 Refrigeration Cycle ee ee 2 Condensers eeren 5 Air Cooled Condensers ee ee ee ee ee ee ee ee 5 Evaporative Condensers ee see see ee ee ee ee 7 Water Cooled Condensers ee ee ee ee ee ee 8 Condenser COMMON SEE ee EE ie ee 10 Evaporators E rose isnt 16 Finned Tube Evaporators eie sees see ee see ee ee ee 16 Shell and Tube Evaporators ese see see ee ee ee ee ee 19 Evaporator Control se ne de Ee 20 Expansion Devices n 26 Accessories ee ee ee ee ee 34 Solenoid Valve RE OE EE EE N 34 Liquid Line Filter Drier insek Se N RE 36 Moisture Indicating Sight Gla
30. modulate the temperature of the water entering the condenser Each of these options has the effect of varying the temperature of the water entering the condenser ensuring an acceptable condensing pressure and temperature Cooling Tower Bypass diverting valve hl _ cooling tower F aa bypass pipe condenser Another example is a system that must start and operate during cooler weather The cold tower water would force the condensing pressure down to the point where the system could not operate In this example the temperature of the water entering the condenser is controlled by a diverting valve and a cooling tower bypass pipe 55 F 13 C 65 F 18 C If the entering water temperature causes the condensing pressure to become too low the valve begins to divert the warm water that is leaving the condenser and mixes it with the cool tower water producing a controlled water temperature entering the condenser In this example by diverting 65 F 18 C water leaving the condenser and mixing it with the 40 F 4 C tower water the condenser is provided with 55 F 13 C condensing water This warmer condensing water results in a higher condensing pressure TRG TRC005 EN 13 S TRANE 14 period two Condensers Air Cooled Condenser Control condenser airflow heat rejection capacity A common method of controlling the capacity of an air cooled condenser is to vary the airflow across the condenser c
31. mproves heat transfer 19 S TRANE 20 period three Evaporators Evaporator Control Evaporator capacity is influenced by Temperature difference between refrigerant and air or water being cooled Flow rate of air or water through evaporator Flow rate of refrigerant through evaporator Evaporator Control The rate of heat exchange within an evaporator is governed by 1 the temperature difference between the refrigerant and the air or water being cooled 2 the flow rate of the air or water through the evaporator and 3 the flow rate of the refrigerant through the evaporator In comfort cooling applications it is necessary to balance the capacity of the system with the ever changing load The flow rate and temperature of the air or water being cooled are typically controlled to respond directly to the system load A constant volume system delivers a constant quantity of air to the space and to maintain the required space temperature at all load conditions varies the temperature of this air In contrast a variable airvolume VAV system delivers air at a constant temperature and varies the airflow to maintain the required space temperature at all load conditions These are variables that the evaporator must respond to rather than directly control The most common method of controlling the capacity of the evaporator at part load is to control the temperature and or flow rate of the refrigerant through the system by un
32. noid valve is to enable system pump down and prevent the refrigerant from migrating through the system when the compressor is shut off In this application a single solenoid valve is installed in the liquid line upstream of all expansion valves 35 36 period five Accessories When the compressor is shut off the evaporator contains a large quantity of liquid refrigerant This can present a problem if some of the refrigerant drains into the suction line and slugs the compressor when it starts up again To prevent this from occurring many systems pump the refrigerant out of the evaporator and suction line before shutting the compressor off This is called a pump down cycle Instead of shutting the compressor off right away the solenoid valve is closed to stop the flow of liquid refrigerant into the evaporator and the compressor is allowed to run for a short period of time The compressor pumps the refrigerant from the low pressure side of the system evaporator and suction line to the high pressure side of the system discharge line condenser and liquid line As the low pressure side of the system is pumped free of refrigerant the pressure in that part of the system drops To end the pump down cycle a pressure sensor is used to shut the compressor off when this pressure reaches a predetermined set point Prior to starting the compressor again the solenoid valve is opened allowing the pressure on the low pressure side of the sys
33. of the refrigerant 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 desired evaporator temperature The cooled mixture of liquid and vapor refrigerant then enters the evaporator A to repeat the cycle 4 TRG TRC005 EN TRG TRCOOS EN period two Condensers Refrigeration System Components period two Condensers The first major component to be discussed is the condenser The condenser is a heat exchanger that rejects heat from the refrigerant to air water or some other fluid The three common types of condensers are air cooled water cooled and evaporative Air Cooled Condenser propeller fan outdoor air ae condenser coil subcooler Air Cooled Condensers A typical air cooled condenser uses propeller type fans to draw outdoor air over a finned tube heat transfer surface The temperature difference between the hot refrigerant vapor that is flowing through the tubes and the cooler outdoor air induces heat transfer The resulting reduction in the heat content of the refrigerant vapor causes it to condense into liquid Within the final few lengths of condenser tubing the subcooler the liquid refrigerant is further cooled below the temperature at which it was condensed period two Condensers The air cooled condenser is very popular in both residential and commercial applications because of i
34. oil The heat rejection rate of a multiple fan condenser is often controlled by cycling fans on and off to maintain acceptable condensing pressures Alternatively the airflow across the coil can be varied by using a damper or a variable speed drive on one or more of the fans In this example a damper has been added to one of the two condenser fans Capacity control is accomplished by cycling fan B on and off while varying the airflow of fan A by modulating the damper Both the damper and the cycled fan are controlled by condensing pressure As the heat rejection requirement increases fan A continues to open its damper farther to increase its airflow When fan A reaches full airflow fan B turns on and fan A modulates its damper to continue to match the desired heat rejection rate Condenser Flooding Control condenser compressor TTT TTT f E ana evaporator Another less common method of controlling the capacity of an air cooled TRG TRCOOS EN TRG TRCOOS EN S TRANE period two Condensers condenser is to flood the condenser coil with liquid refrigerant A condenser coil tube that is filled with liquid refrigerant no longer acts as a condensing surface Progressive flooding of the condenser coil tubes reduces the capacity of the condenser and raises the condensing pressure During normal warm ambient conditions valves B and C are open and valve A is closed Assume that the system load is falling and at th
35. oil in a constant volume application which section top or bottom of the coil should be activated first and deactivated last TRG TRCOOS EN S TRANE Quiz Questions for Period 4 10 What are the two primary purposes of a thermostatic expansion valve 11 What are the risks of too much superheat in the system Questions for Period 5 12 During a pump down cycle the compressor pumps the refrigerant from the low or high pressure side of the system to the low or high pressure side 13 Is the moisture indicating sight glass installed upstream or downstream of the expansion valve TRG TRCOOS EN A9 50 Answers a BO N N BtoC F to G Air cooled evaporative and water cooled A decrease in system load and a reduction in the outdoor air temperature Varying the airflow through the condenser coil or flooding the condenser coil with liquid refrigerant A distributor To direct the water in a rising and falling flow path over the tubes that carry the refrigerant resulting in turbulence that improves heat transfer Face split intertwined and row split Bottom section 10 The thermostatic expansion valve a maintains the pressure difference between the high pressure and low pressure sides of the system and b maintains the proper amount of superheat in the system by metering the quantity of liquid refrigerant entering the evaporator ensuring it will be completely vaporized within the evaporator
36. ools the remaining water This cooled water then falls to the tower sump to be returned to the condenser The final temperature of the water leaving the tower is determined in part by the humidity of the outdoor air If the outdoor air is dry the final water temperature can be considerably lower than the ambient dry bulb temperature If the outdoor air is humid however the final temperature will be near the ambient dry bulb temperature While a cooling tower can reclaim much of the condensing water it cannot reclaim it all The evaporation process uses up water to dissipate heat contributed by the cooling load plus the heat of compression In addition as the water evaporates the dissolved minerals and water treatment chemicals become concentrated in the sump To prevent this solution from becoming concentrated and possibly corrosive water is periodically bled from the sump and an equal amount of fresh water is added In the past some water cooled condensers used water from either a municipal or a natural water supply as the condensing water After rejecting the condenser heat to this water it was dumped into the sewer or back into the body of water Environmental and economic restrictions have made this method uncommon Finally a geothermal well system can be used to reject the heat from the condenser by circulating the condensing water through a series of underground pipes This method takes advantage of the naturally cool ground t
37. peratures leaving the upstream section of coil hamper the ability of the downstream section of coil to provide adequate superheat Row split coils are generally not recommended for comfort cooling applications When applied they require careful coil selection expansion valve sizing and selection and control Shell and Tube Evaporator Control shell and tube evaporator refrigerant vapor liquid refrigerant expansion valve The capacity of a shell and tube evaporator is primarily controlled by the unloading or cycling of compressors However as with a finned tube evaporator it also uses an expansion valve to control the flow rate of refrigerant through the evaporator and ensure the proper amount of superheat in the system A shell and tube evaporator may also contain more than one liquid refrigerant circuit each served by one expansion valve 25 S TRANE 26 period four Expansion Devices Refrigeration System Components period four Expansion Devices The final major component to be discussed is the expansion device Expansion Device condenser compressor D Cc D p 2 expansion D device O A evaporator enthalpy An expansion device is used to maintain a pressure difference between the high pressure condenser and low pressure evaporator sides of the system established by the compressor This pressure difference allows the evaporator temperature to be low enough to absorb heat from
38. s provide good part load humidity control although potentially not as good as face split coils 23 24 period three Evaporators Row Split Arrangement Finally the row split coil configuration also called vertical split or series flow places the independently controlled coil sections in series in the airstream All of the air passes through both coil sections one before the other Typically the first few upstream rows of the coil are served by one distributor and the remaining downstream rows by another distributor At lower loads only the downstream section is active At higher loads the full depth of the coil Is active Row Split Arrangement 10 F 21 C 80 F 27 C Row split coils are very difficult to split into equal capacity sections Since the air entering the downstream section of coil has already been cooled somewhat by the upstream section of coil the air to refrigerant temperature difference is much smaller Therefore the downstream section of coil requires more rows of tubes to deliver about the same capacity as the upstream section of coil A common row split arrangement uses two rows for the upstream section and TRG TRCOOS EN TRG TRCOOS EN S TRANE period three Evaporators four rows for the downstream section This is an attempt to ensure near equal loading of the two coil sections when both are active A second concern involves the control of superheat The cooler tem
39. ses at part load conditions Therefore face split coils are well suited for constant volume applications They provide better part load humidity control than could be obtained from a large coil controlled by a single expansion valve In a constant volume application the lower section of a face split coil should be activated first and deactivated last This sequence prevents moisture that has condensed from the air flowing through the active coil section from flowing over the fins of the inactive coil section where it could carry over into the supply airstream TRG TRCOOS EN TRG TRCOOS EN period three Evaporators Intertwined Arrangement The intertwined coil configuration splits the coil sections by alternating the tubes fed in each row between two distributors At lower loads liquid refrigerant is fed to every other tube of the coil and therefore it behaves like a coil with substantially greater fin surface At higher loads refrigerant is fed to all of the tubes in the coil Because of the increased fin surface available at part load conditions the coil surface does not have to be as cold to provide a constant leaving air temperature This reduces the potential for coil frosting Therefore intertwined coils are better suited for VAV applications Part load humidity control is less of an issue with VAV applications due to the constant cold leaving air temperature In constant volume applications intertwined coil
40. sing coil The principal advantage of this design is that the centrifugal fan is capable of overcoming the higher static pressure losses associated with ductwork Therefore if the condenser is to be located indoors and uses a duct system to deliver air to and from the condenser coil the centrifugal fan air cooled condenser is probably best suited for this application Evaporative Condenser refrigerant vapor condenser liquid refrigerant subcooler Evaporative Condensers A modification of the air cooled condenser is the evaporative condenser Within this device the refrigerant flows through tubes and air is drawn or blown over the tubes by a fan The difference is that water is sprayed on the tube surfaces As the air passes over the coil it causes a small portion of the water to evaporate This evaporation process absorbs heat from the coil period two Condensers causing the refrigerant vapor within the tubes to condense The remaining water then falls to the sump to be recirculated and used again Subcooling of the refrigerant can be accomplished by piping the condensed liquid back through another few rows of coil tubing located either in the condenser airstream or in the water sump where additional heat transfer reduces the temperature of the liquid refrigerant Water Cooled Condenser hot refrigerant vapor 95 F 35 C paa cooling water b 85 F eo subcooler subcool
41. ss oo ee ee ee 38 UCHN bie FIET oa EE E Eh 39 Hot GaS MUTIGI sesse RE EG ie 40 MUON ER ON RE EE N 41 PCC SS ONL cscs ys E oe Ge EE Ee ER 42 Review sacar tee ris seearscesaereetaee tase narracsimendoncines 43 Quiz ee ee eed A8 Answers ee ee ee ee ee ee ee ee sen 50 Glossary i r 51 TRG TRCOOS EN Introduction Vapor Compression Refrigeration expansion device compressor The major components of a vapor compression refrigeration system include the compressor condenser expansion device and evaporator The latter three will be discussed in this clinic the compressor is discussed in a separate clinic This clinic will also discuss many of the common accessories used in a comfort cooling refrigeration system TRG TRCOOS EN 1 S TRANE period one Refrigeration Cycle Refrigeration System Components period one Refrigeration Cycle First a brief review of the vapor compression refrigeration cycle will help to relate these components Refrigeration Cycle pressure A evaporator B enthalpy A diagram of a typical vapor compression refrigeration cycle can be superimposed on a pressure enthalpy P h chart to demonstrate the function of each component in the system 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
42. t vapor absorbs even more heat When the liquid refrigerant has completely evaporated this additional heat gain to the vapor is called superheating Superheating the refrigerant vapor the line from B to C shifts it away from the liquid vapor region and ensures that the refrigerant vapor is completely free of liquid prior to traveling to the compressor TRG TRCOOS EN TRG TRCOOS EN period three Evaporators Shell and Tube Evaporator chilled water gt supply chilled baffles water return refrigerant y vapor liquid vapor refrigerant tube bundle Shell and Tube Evaporators Instead of producing cooled air a shell and tube evaporator is used to produce chilled water In this type of evaporator the cool liquid refrigerant flows through the tubes and water fills the shell space surrounding the tubes 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 Water enters the shell at one end and leaves at the opposite end This chilled water is pumped to one or more heat exchangers to handle the system cooling load These heat exchangers could be coils used to cool air or they could be some other load that requires chilled water Shell and Tube Evaporator baffles Baffles within the shell direct the water in a rising and falling flow path over the tubes that carry the refrigerant This results in turbulence that i
43. tdoor air upward through the fill distributor A device used to ensure uniform refrigerant distribution through the multiple coil circuits of a finned tube evaporator electronic expansion valve A type of expansion device that uses an electronically actuated valve to sense and control the flow rate of liquid refrigerant to the evaporator enthalpy The property of a refrigerant indicating its heat content both sensible and latent per pound kg of refrigerant evaporative condenser A type of condenser where refrigerant flows through the tubes and rejects heat to air The air is drawn across the tubes which are wetted on the outside by circulating water evaporator The component of the refrigeration system where cool liquid refrigerant absorbs heat from air water or some other fluid causing the refrigerant to boil expansion device The component of the refrigeration system used to reduce the pressure and temperature of the refrigerant expansion valve The type of expansion device that maintains the pressure difference between the high pressure and low pressure sides of the system It also maintains the proper amount of superheat in the system by metering the quantity of liquid refrigerant entering the evaporator ensuring that the refrigerant will be completely vaporized within the evaporator 51 52 Glossary face split A type of finned tube evaporator arrangement that splits the coil into parallel air paths fill The
44. tem to Increase again The solenoid valve should be installed as close to the expansion valve as possible This will minimize the pump down time and allow the liquid line to be used for storing refrigerant when the system is off Liquid Line Filter Drier liquid line liquid line expansion filter drier p valve solenoid valve evaporator Liquid Line Filter Drier The next accessory to be discussed the liquid line filter drier is installed upstream of the solenoid valve and the expansion valve It prevents moisture water and foreign matter introduced during the installation process from entering the expansion valve and the solenoid valve Realize however that there is no substitute for cleanliness during system installation Moisture and foreign matter can cause problems in any refrigeration system When water is mixed with refrigerant and oil and heat is added by the compressor acids are formed that can damage the valves or compressor Additionally certain foreign materials such as copper and brass particles can TRG TRCOOS EN TRG TRCOOS EN S TRANE period five Accessories act as a catalyst in chemical reactions that result in the formation of acids These acids can corrode system components and cause the oil to sludge The filter drier should be installed close to the solenoid valve to provide the most protection for the solenoid and expansion valves Liquid Line Filter Drier
45. that fills the surrounding shell 53 Literature Order Number TRG TRCOOS EN S TRANE File Number E AV FND TRG TRC005 1199 EN The Trane Company 2 B Worldwide Applied Systems Group Supersedes 2803 3 784 and 2803 5 1284 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
46. the air or water to be cooled while also allowing the refrigerant to be at a high enough temperature in the condenser to reject heat to air or water at normally available temperatures There are several types of expansion devices including expansion valves thermostatic or electronic capillary tubes and orifices This clinic will limit its discussion to thermostatic expansion valves TXVs Other expansion devices perform essentially the same function TRG TRCOOS EN S TRANE period Tour Expansion Devices Thermostatic Expansion Valve Ed Es TT thermostatic RR RAREEEF EE tetas am expansion se TF s t oa Fe EE KEER valve TXV E e ee ee LETE EEEE te J liquid evaporator ff eames mad refrigerant N DU AM DEE ED eN liquid vapor BEERS B mixture E paapa BS ee ee ee AILL ig AER A A GEELES i LETHA e S 1E AH e e H EEN t L refrigerant af vapor In addition to maintaining a pressure difference the thermostatic expansion valve controls the guantity of liduid refrigerant entering the evaporator lt ensures that the refrigerant will be completely vaporized within the evaporator A and maintains the proper amount of superheat in the system TXV Control liguid refrigerant liquid vapor mixture refrigerant vapor If not enough liquid refrigerant enters the evaporator it vaporizes too quickly A As a result the remaining coil tubes fill with vapor producing very little refrig
47. the refrigerant Unfortunately if the condensing pressure falls too low the expansion valve may not be able to produce the flow of liquid refrigerant needed to satisfy the demand at the evaporator In some systems as the condensing pressure drops the compressor suction pressure also drops resulting in evaporator frosting and possible compressor shutdown due to a low pressure safety device While it is not essential to control condensing pressure to a constant value provisions should be made to control it within acceptable limits Condensing Temperature Control flow regulating condenser water pump One common method of controlling the capacity of a water cooled condenser is to vary the rate at which water flows through the condenser For example assume a water cooled condenser Is piped to a municipal water system To control the capacity of the condenser a flow regulating valve is installed on the leaving water side of the condenser As the load on the system decreases the regulating valve senses the lowering condensing pressure The valve reduces the flow rate of the water until the heat rejection rate of the condenser balances the system load at an acceptable pressure and temperature 11 S TRANE 12 period two Condensers Vary Condenser Water Flow Rate cooling tower mm variable speed drive It is more common however for a water cooled condenser to be connected to a cooling tower In
48. this case typical methods for modulating the water flow through the condenser include either using a variable speed drive on the condenser water pump or using a diverting valve and pipe to bypass the condenser The variable speed drive on the pump modulates the amount of water pumped through the condenser The diverting valve modulates the water flow through the condenser bundle by diverting some of the cooling water around the condenser through the bypass pipe directly back to the cooling tower Each of these options has the effect of varying the flow rate of water through the condenser ensuring an acceptable condensing pressure and temperature Vary Entering Water Temperature variable speed W drive cooling tower bypass pipe diverting valve condenser Another method of controlling the capacity of a water cooled condenser is to vary the temperature of the water entering the condenser TRG TRCOOS EN S TRANE period two Condensers Common methods of modulating this water temperature include controlling the cooling tower fans or using a cooling tower bypass pipe Controlling the cooling tower fans either by cycling fans on and off or by using a variable speed drive on the fans allows the system to control the temperature of the water leaving the tower sump The diverting valve on the cooling tower bypass pipe diverts warmer water leaving the condenser and mixes it with cooler water from the cooling tower to
49. ts convenience It requires very little maintenance and does not require the freeze protection and water treatment that is necessary with a water cooled condenser Additionally it is favored in areas that have an inadequate or costly water supply or where the use of water for air conditioning is restricted Effect of Subcooling subcooling pressure refrigeration effect enthalpy The benefit of subcooling on system performance can be demonstrated by comparing the performance of a system with and without subcooling The change in enthalpy the line from A to B that occurs in the evaporator is called the refrigeration effect This is the amount of heat that each pound kg of liquid refrigerant will absorb when it evaporates In comparison the same system without subcooling produces less refrigeration effect the line from A to B The system without subcooling must evaporate substantially more refrigerant within a larger coil to produce the same capacity as the system with subcooling Instead of subcooling in the condenser some packaged refrigeration equipment such as water chillers may use an economizer or liquid vapor separator to increase this refrigeration effect TRG TRCOOS EN TRG TRCOOS EN S TRANE period two Condensers Centrifugal Fan Air Cooled Condenser condenser coil centrifugal fan An alternative air cooled condenser uses a centrifugal fan to draw or blow air over the conden
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