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Air Conditioning Clinic Absor ption W at er Chillers One of the Equipment Ser ies TRG-TR C0 1 1 -EN.
Absor ption W at er Chillers One of the Equipment Ser ies A publication of The T rane Compan y— W o rldwide Applied S ystems Group.
Pr ef ace © 20 0 0 American Standard Inc. All rights reserved TRG-TRC0 1 1 -EN ii The T rane Compan y believes that it is incumbent on manufacturer s to serve the industry by regularly disseminating information gathered through laboratory researc h, testing programs, and field experience.
TRG-TRC0 1 1 -EN iii Cont ents Introduction ........................................................... 1 period one Absorption Refrigeration Cycle ....................... 3 Absorption System Fluids ........................................ 6 Components of the Absorption Cycle .
iv TRG-TRC0 04-EN.
TRG-TRC0 1 1 -EN 1 notes Intr oduction W ater c hillers 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.
2 TRG-TRC0 1 1 -EN notes Intr oduction W ater c hillers using the vapor -compression refrigeration cycle vary by the type of compressor used. The compressor works to draw in refrigerant vapor and increase its pressure and temperature to create the cooling effect.
TRG-TRC0 1 1 -EN 3 notes period one Absor ption Refr iger ation Cy cle This period describes the components of the absorption refrigeration cycle. Comparing the absorption refrigeration cycle with the more familiar vapor - compression refrigeration cycle is often an easy w ay to introduce it.
4 TRG-TRC0 1 1 -EN notes period one Absor ption Refr iger ation Cy cle In the vapor -compression refrigeration cycle, refrigerant enters the evaporator in the form of a cool, low- pressure mixture of liquid and vapor ( $ ). Heat is transferred from the relatively warm air or w ater to the refrigerant, causing the liquid refrigerant to boil.
TRG-TRC0 1 1 -EN 5 period one Absor ption Refr iger ation Cy cle notes There are two fundamental differences between the absorption refrigeration cycle and the vapor -compression refrigeration cycle. The first is that the compressor is replaced by an absorber , pump, and generator .
6 TRG-TRC0 1 1 -EN notes period one Absor ption Refr iger ation Cy cle Absorption System Fluids Probably the greater of these dif ferences between the vapor -compression and absorption refrigeration cycles, however , is the types of fluids used.
TRG-TRC0 1 1 -EN 7 period one Absor ption Refr iger ation Cy cle notes Additionally , the absorption refrigerant cycle uses a second fluid called an absorbent solution.
8 TRG-TRC0 1 1 -EN notes period one Absor ption Refr iger ation Cy cle These two fluids, the refrigerant and the absorbent, are mixed inside the c hiller in various concentrations. The term dilute solution refers to a mixture that has a relatively high refrigerant content and low absorbent content.
TRG-TRC0 1 1 -EN 9 period one Absor ption Refr iger ation Cy cle notes The operating conditions used in this section of the clinic are approximate, subject to variation with c hanging load and cooling-water temperature conditions.
10 TRG-TRC0 1 1 -EN notes period one Absor ption Refr iger ation Cy cle Starting on the high-pressure side of the cycle, the purpose of the generator is to deliver the refrigerant vapor to the rest of the system. It accomplishes this by separating the water (refrigerant) from the lithium bromide-and-w ater solution.
TRG-TRC0 1 1 -EN 11 period one Absor ption Refr iger ation Cy cle notes Inside the condenser , cooling water flows through tubes and the hot refrigerant vapor fills the surrounding space. As heat transfers from the refrigerant vapor to the water , refrigerant condenses on the tube surfaces.
12 TRG-TRC0 1 1 -EN notes period one Absor ption Refr iger ation Cy cle As the high-pressure liquid refrigerant flows through the expansion device, it causes a pressure drop that reduces the refrigerant pressure to that of the evaporator .
TRG-TRC0 1 1 -EN 13 period one Absor ption Refr iger ation Cy cle notes Inside the absorber , the refrigerant vapor is absorbed by the lithium bromide solution. As the refrigerant vapor is absorbed, it condenses from a vapor to a liquid, releasing the heat it acquired in the evaporator .
14 TRG-TRC0 1 1 -EN notes period one Absor ption Refr iger ation Cy cle As the lithium bromide solution absorbs the refrigerant, it becomes diluted and has less ability to absorb water vapor . T o complete the cycle and sustain operation, the absorbent solution must be reconcentrated.
TRG-TRC0 1 1 -EN 15 period one Absor ption Refr iger ation Cy cle notes Equilibrium Chart The performance of the absorption refrigeration cycle can be analyzed using a special c hart called an Equilibrium Chart for Aqueous Lithium Bromide Sol u ti o ns .
16 TRG-TRC0 1 1 -EN notes period one Absor ption Refr iger ation Cy cle A diagram of a typical absorption refrigeration cycle can be superimposed on this equilibrium c hart to demonstrate the function of eac h component in the system.
TRG-TRC0 1 1 -EN 17 period one Absor ption Refr iger ation Cy cle notes Starting at the absorber , the dilute lithium bromide solution leaves the absorber ( $ ) at 1 05 ° F [40.6 º C] and 59% concentration. This solution passes through the heat exc hanger , where it is preheated to 175 ° F [79.
18 TRG-TRC0 1 1 -EN notes Lithium bromide-and-water absorption c hillers are classified by the firing method — that is, how the primary generator is heated and whether it has a single- or a multiple-effect generator .
TRG-TRC0 1 1 -EN 19 period t w o Absor ption Chiller T ypes notes Single-Ef fect Chiller The single-ef fect absorption w ater c hiller uses a cycle similar to the one presented in Pe riod One. It includes a single generator , condenser , evaporator , absorber , heat exc hanger , and pumps.
20 TRG-TRC0 1 1 -EN notes period t w o Absor ption Chiller T ypes Let us review P eriod One briefly . In the generator , dilute solution absorbs heat from the steam or hot water , causing the refrigerant to boil and separate from the absorbent solution.
TRG-TRC0 1 1 -EN 21 period t w o Absor ption Chiller T ypes notes Double-Ef fect Chiller The double-effect absorption c hiller includes the same basic components as the single-effect c hiller; however , it also includes an additional generator , heat exc hanger , and pump.
22 TRG-TRC0 1 1 -EN notes period t w o Absor ption Chiller T ypes In the high-temperature generator , very high temperature steam or hot water flows through tubes that are immersed in an absorbent solution that is at an intermediate concentration.
TRG-TRC0 1 1 -EN 23 period t w o Absor ption Chiller T ypes notes Next, the refrigerant travels through the condenser , expansion device, evaporator and absorber in a manner similar to refrigerant travel in the single- effect absorption c hiller .
24 TRG-TRC0 1 1 -EN notes period t w o Absor ption Chiller T ypes to the absorber reduces the flow rate of cooling water required through the absorber .
TRG-TRC0 1 1 -EN 25 period t w o Absor ption Chiller T ypes notes In the series flow cycle, the dilute solution from the absorber is pumped entirely to the high-temperature generator . As the refrigerant boils away and migrates to the low-temperature generator , the absorbent solution becomes concentrated.
26 TRG-TRC0 1 1 -EN notes period t w o Absor ption Chiller T ypes In the parallel flow cycle, the dilute solution from the absorber is split between the low-temperature and high-temperature generators. Both streams of dilute solution are concentrated in the generators and mix together again before returning to the absorber .
TRG-TRC0 1 1 -EN 27 period t w o Absor ption Chiller T ypes notes Direct-Fired Chiller The indirect-fired absorption c hiller s discussed previously use steam or a hot liquid (suc h as water) as the energy source.
28 TRG-TRC0 1 1-EN notes period t w o Absor ption Chiller T ypes separate from the absorbent solution. As the refrigerant boils away , the solution becomes concentrated and returns to the absorber .
TRG-TRC0 1 1-EN 29 period t w o Absor ption Chiller T ypes notes The high-temperature generator pump draws a portion of the intermediate solution from the low-temperature generator and delivers it to the high- temperature generator to be reconcentrated.
30 TRG-TRC0 1 1-EN notes period t w o Absor ption Chiller T ypes Chiller/Heater One of the benefits of a direct-fired absorption c hiller is that it can be used to provide both cooling and heating. These c hillers, therefore, can be installed in systems to supplement, or even replace, primary heating or domestic hot water equipment.
TRG-TRC0 1 1-EN 31 period t w o Absor ption Chiller T ypes notes Eac h of these operating modes serves a different load requirement. n In cooling only mode, the absorption c hiller operates exactly like the standard c hiller offering. Its function is to make cold water .
32 TRG-TRC0 1 1-EN notes period t w o Absor ption Chiller T ypes An alternate method is to use the evaporator as a condenser in the heating mode. In this example c hiller , by switc hing the cooling/h.
TRG-TRC0 1 1-EN 33 period t w o Absor ption Chiller T ypes notes While they are presently not available, higher -effect absorption c hillers are being studied for commercial use due their potential for higher COPs. T ypical COPs for these triple-effect cycles are 1 .
34 TRG-TRC0 1 1-EN notes period three Capacity Contr ol The primary objective of the chiller capacity control system is to reliably maintain the temperature of the c hilled water leaving the evaporator .
TRG-TRC0 1 1-EN 35 period three Capacity Contr ol notes other words, the combination of solution temperature and concentration determines the temperature at whic h the refrigerant will boil (vaporize). V arying the temperature at whic h the refrigerant boils in the evaporator c hanges the capacity of the absorption water c hiller .
36 TRG-TRC0 1 1-EN notes period three Capacity Contr ol In more modern absorption c hiller designs, adjustable-frequenc y driv es (AFD) , also known as variable-speed drives, are used to vary the speed of the generator pump motor , thus reducing the flow of solution to the generator .
TRG-TRC0 1 1-EN 37 period three Capacity Contr ol notes out of the condition called crystallization — a solidification of the bromide salt. Crystallization will be discussed next. In the past, absorption water c hiller s would vary the heat input to the generator as the primary means of maintaining the desired leaving-c hilled-water temperature.
38 TRG-TRC0 1 1-EN notes period three Capacity Contr ol By plotting the single-ef fect absorption refrigeration cycle on the equilibrium c hart, it is apparent that crystallization is most likely to occur in the heat exc hanger . At this par ticular condition, the 65% concentrated solution ( ' ) is cooled to 135 ° F [57 .
TRG-TRC0 1 1-EN 39 period three Capacity Contr ol notes As discussed, the point at whic h crystallization occur s is determined by the temperature and concentration of the concentrated solution inside the heat exc hanger .
40 TRG-TRC0 1 1-EN notes period three Capacity Contr ol its way into the c hiller through any available path. As explained earlier , the pressure and temperature inside the evaporator are determined by the concentration and temperature of the solution in the absorber .
TRG-TRC0 1 1-EN 41 period three Capacity Contr ol notes operate over a wide cooling-w ater temperature range, allowing the cooling- water temperature to vary with the load and ambient conditions without the risk of crystallization.
42 TRG-TRC0 1 1-EN notes period three Capacity Contr ol As a second line of defense, most absorption water c hillers include devices that allow the c hiller to recover in the event that crystallization does occur . Some of these devices simply sense impending crystallization, put the c hiller through a dilution cycle, and shut the c hiller down.
TRG-TRC0 1 1-EN 43 period three Capacity Contr ol notes Special consideration must be given to controlling the chiller at very low load conditions combined with low cooling water temperatures. Under these conditions, the c hiller reac hes equilibrium with a very low solution concentration in the absorber .
44 TRG-TRC0 1 1-EN notes period three Capacity Contr ol Pur g e Sys t e m As presented earlier , the accumulation of air and other noncondensable gases undermines the efficiency and reliability of the absorption c hiller .
TRG-TRC0 1 1-EN 45 period three Capacity Contr ol notes This example purge system consists of a purge tank, a small refrigeration system, a pump-out system, and controls. The purge ’ s refrigeration system includes: a small compressor , an air -cooled condensing coil, an expansion valve, and an evaporator coil located inside of the purge tank.
46 TRG-TRC0 1 1-EN notes period f our Maint enance Considerations T oday , af ter an absorption c hiller is installed and put into operation, it functions without a full-time attendant. In most cases, the c hiller starts and stops on a sc hedule controlled by a building automation system or a simple time cloc k.
TRG-TRC0 1 1-EN 47 period f our Maint enance Considerations notes condenser inlet and outlet temperatures; and purge operation. Logs are a valuable tool for determining the onset of system problems. This data may be obtained either manually or in conjunction with a building automation system.
48 TRG-TRC0 1 1-EN notes period f our Maint enance Considerations Most purges are fully automatic and generally require less maintenance than previous-generation manually operated purges.
TRG-TRC0 1 1-EN 49 period f our Maint enance Considerations notes The burner is the heart of a direct-fired absorption c hiller . Cor rect operation is, therefore, necessary for optimum c hiller performance. Daily c hec ks should be made in accordance with the manufacturer ’ s recommendations.
50 TRG-TRC0 1 1-EN notes period f our Maint enance Considerations The use of better heat-transfer materials will reduce future maintenance costs. The high-temperature generator , for example, contains.
TRG-TRC0 1 1-EN 51 period f our Maint enance Considerations notes An absorption c hiller requires a very deep vacuum to operate efficiently . The introduction of air and other noncondensables into the c hiller will adver sely affect the c hiller ’ s performance.
52 TRG-TRC0 1 1-EN notes period f our Maint enance Considerations If air leaks into the c hiller , the cor rosion inhibitor is depleted as it reacts with the air and produces hydrogen.
TRG-TRC0 1 1-EN 53 notes period fiv e Application Consider ations Several considerations must be addressed when applying absorption w a ter c hiller s, including: n Cooling-water temperature limitatio.
54 TRG-TRC0 1 1-EN notes period fiv e Application Consider ations Cooling-Water T emperature Limitations The temperature of the cooling water significantly impacts the operation of an absorption c hiller . As the temperature of the entering-cooling-w ater decreases, c hiller capacity increases.
TRG-TRC0 1 1-EN 55 period fiv e Application Consider ations notes Combination Chiller Plants Absorption c hiller s possess two operating c haracteristics that can noticeably improve o verall system ef ficiency and reduce system energy costs. First, absorption c hillers use fossil fuels rather than electricity .
56 TRG-TRC0 1 1-EN notes period fiv e Application Consider ations The second beneficial operating c haracteristic is that an absorption c hiller works more efficiently and produces more cooling with increased leaving- c hilled-water temperatures. Applications with two c hiller s can be either piped in series or in parallel.
TRG-TRC0 1 1-EN 57 period fiv e Application Consider ations notes Special Considerations for Direct-Fired Chillers The combustion process that occurs in the burner is k ey to the operation of a direct-fired absorption c hiller . It also introduces several additional considerations when applying this type of c hiller .
58 TRG-TRC0 1 1-EN notes period fiv e Application Consider ations In general, ASHRAE Standard 1 5-1 994, “ Safety Code for Mec hanical Refrigeration, ” does not apply to absorption w ater c hiller s due to Section 2.3, whic h states: This code does not apply where water is the primary refrigerant.
TRG-TRC0 1 1-EN 59 period fiv e Application Consider ations notes a refrigerant vapor detector to monitor refrigerant levels in the mac hinery room. When the detector measures refrigerant levels above those allow able, a building automation system is used to automatically shut down the combustion process.
60 TRG-TRC0 1 1-EN notes W e will now review the main concepts that were covered in this clinic on absorption water c hillers. P eriod One presented the basic single-ef fect, absorption refrigeration cycle.
TRG-TRC0 1 1-EN 61 period six Review notes and vapor refrigerant then flows into the ev aporator pan, from whic h the ev aporator spra y pump continuously pumps the liquid refrigerant to be sprayed o ver the tubes.
62 TRG-TRC0 1 1-EN notes period six Review Pe riod Three explained the part-load operation of the absorption c hiller . It described the use of energy valves, burner controls, throt tling and bypass valves, and adjustable-frequency drives as methods for controlling the capacity on the c hiller .
TRG-TRC0 1 1-EN 63 period six Review notes P eriod Four described general maintenance requirements for absorption w ater c hiller s, including: n Recommended data for a daily log n Recommended mainten.
64 TRG-TRC0 1 1-EN notes period six Review For more information, refer to the following references: n T rane product catalogs for absorption water c hiller products (T rane literature order numbers AB.
TRG-TRC0 1 1-EN 65 Questions f or P eriod 1 1 What are the names of the two working fluids used within the absorption cycle? 2 Identify the components of the absorption refrigeration cycle labeled in Figure 75.
66 TRG-TRC0 1 1-EN Quiz Questions f or P eriod 3 9 Does an increase in solution concentration, assuming a constant solution temperature, result in an increase or decrease in vapor pressure? 10 What is.
TRG-TRC0 1 1-EN 67.
68 TRG-TRC0 1 1-EN 1 Refrigerant (distilled w ater) and absorbent (lithium bromide) 2 $ generator , % condenser , & expansion device, ' evaporator , ( absorber , ) heat exc hanger 3 Generator.
TRG-TRC0 1 1-EN 69 absorbent A substance used to absorb refrigerant and transport it from the low-pressure to the high-pressure side of the absorption refrigeration cycle.
70 TRG-TRC0 1 1-EN Glossary condenser A component of the absorption refrigeration system in whic h refrigerant vapor is conver ted to liquid as it rejects heat to cooling water . cooling wat er W ater obtained from a source (cooling tower , river , pond) to whic h heat is rejected.
TRG-TRC0 1 1-EN 71 Glossary purg e A device used to remove air and other noncondensable gases that may leak into the low-pressure absorption c hiller . re f rig e ra n t A substance used to absorb and transport heat for the purpose of cooling. In a large absorption water c hiller, the refrigerant is distilled w ater .
The T rane Company W orldwide Applied S ystems Group 3600 Pammel Creek Road La Crosse, WI 5460 1 -7599 www.trane.com An American Standard Company Literature Order Number TRG-TRC0 1 1 -EN File Number E.
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