Page 2 - One of the Equipment Series
AbsorptionWater Chillers One of the Equipment Series A publication ofThe Trane Company—Worldwide Applied Systems Group
Page 3 - Preface; ii; absorption water chillers
Preface © 2000 American Standard Inc. All rights reserved TRG-TRC011-EN ii The Trane Company believes that it is incumbent on manufacturers to serve the industry by regularly disseminating information gathered through laboratory research, testing programs, and field experience. The Trane Air Conditi...
Page 4 - iii; Contents
TRG-TRC011-EN iii Contents Introduction ........................................................... 1 period one Absorption Refrigeration Cycle ....................... 3 Absorption System Fluids ........................................ 6 Components of the Absorption Cycle ...................... 8 Eq...
Page 5 - iv
Page 6 - notes; Introduction; Systems that employ water chillers are commonly called; systems
TRG-TRC011-EN 1 notes Introduction 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...
Page 8 - Absorption Refrigeration Cycle; period one
TRG-TRC011-EN 3 notes period one Absorption Refrigeration Cycle 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 way to introduce it. Like the vapor-c...
Page 9 - ) is then pumped from the
4 TRG-TRC011-EN notes period one Absorption Refrigeration Cycle 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 water to the refrigerant, causing...
Page 10 - ). Heat is transferred from the relatively warm water to the
TRG-TRC011-EN 5 period one Absorption Refrigeration Cycle 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. The second is that, in add...
Page 11 - Absorption System Fluids; refrigerant
6 TRG-TRC011-EN notes period one Absorption Refrigeration Cycle Absorption System Fluids Probably the greater of these differences between the vapor-compression and absorption refrigeration cycles, however, is the types of fluids used. The vapor-compression refrigeration cycle generally uses a haloc...
Page 12 - absorbent; solution. The absorbent solution is confined to the absorber and
TRG-TRC011-EN 7 period one Absorption Refrigeration Cycle notes Additionally, the absorption refrigerant cycle uses a second fluid called an absorbent solution. The absorbent solution is confined to the absorber and generator sections of the cycle, and is used to carry the refrigerant from the low-p...
Page 13 - dilute solution; refers to a mixture that; concentrated solution; has a relatively low refrigerant content and high; intermediate solution; is a mixture of dilute and; Components of the Absorption Cycle
8 TRG-TRC011-EN notes period one Absorption Refrigeration Cycle These two fluids, the refrigerant and the absorbent, are mixed inside the chiller in various concentrations. The term dilute solution refers to a mixture that has a relatively high refrigerant content and low absorbent content. A concen...
Page 15 - Starting on the high-pressure side of the cycle, the purpose of the; generator; is
10 TRG-TRC011-EN notes period one Absorption Refrigeration Cycle 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-water ...
Page 16 - Inside the; , cooling water flows through tubes and the hot; expansion device
TRG-TRC011-EN 11 period one Absorption Refrigeration Cycle 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. The condensed li...
Page 17 - evaporator; , relatively warm return water from the chilled-water; evaporator pump; draws the liquid
12 TRG-TRC011-EN notes period one Absorption Refrigeration Cycle 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. This pressure reduction causes a small portion of the liquid refrige...
Page 18 - absorber; , the refrigerant vapor is absorbed by the lithium bromide; absorber spray pump; mixes concentrated absorbent solution (returning from
TRG-TRC011-EN 13 period one Absorption Refrigeration Cycle 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. This heat, along wi...
Page 19 - generator pump; continuously returns the dilute solution to the generator to; heat exchanger; . This transfer of heat preheats the dilute solution, reducing the
14 TRG-TRC011-EN notes period one Absorption Refrigeration Cycle As the lithium bromide solution absorbs the refrigerant, it becomes diluted and has less ability to absorb water vapor. To complete the cycle and sustain operation, the absorbent solution must be reconcentrated. Consequently, the gener...
Page 20 - Equilibrium Chart; Equilibrium Chart for Aqueous Lithium Bromide
TRG-TRC011-EN 15 period one Absorption Refrigeration Cycle notes Equilibrium Chart The performance of the absorption refrigeration cycle can be analyzed using a special chart called an Equilibrium Chart for Aqueous Lithium Bromide Solutions . This chart plots the vapor pressure (vertical axis) versu...
Page 22 - The concentrated solution (
TRG-TRC011-EN 17 period one Absorption Refrigeration Cycle notes Starting at the absorber, the dilute lithium bromide solution leaves the absorber ( $ ) at 105 °F [40.6 ºC] and 59% concentration. This solution passes through the heat exchanger, where it is preheated to 175 °F [79.4 °C] ( % ). (Notic...
Page 23 - period two; Absorption Chiller Types
18 TRG-TRC011-EN notes Lithium bromide-and-water absorption chillers 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. Indirect-fired chillers are heated with steam or a hot liquid (such as water) that is typ...
Page 24 - Single-Effect Chiller; The; coefficient of performance
TRG-TRC011-EN 19 period two Absorption Chiller Types notes Single-Effect Chiller The single-effect absorption water chiller uses a cycle similar to the one presented in Period One. It includes a single generator, condenser, evaporator, absorber, heat exchanger, and pumps. These chillers are typicall...
Page 26 - Double-Effect Chiller
TRG-TRC011-EN 21 period two Absorption Chiller Types notes Double-Effect Chiller The double-effect absorption chiller includes the same basic components as the single-effect chiller; however, it also includes an additional generator, heat exchanger, and pump. The high-temperature generator can use s...
Page 27 - In the; high-temperature generator; , very high temperature steam or hot; low-temperature generator; , where it flows through tubes that are
22 TRG-TRC011-EN notes period two Absorption Chiller Types 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. The solution absorbs heat from the warmer steam or water, c...
Page 28 - low-temperature generator pump
TRG-TRC011-EN 23 period two Absorption Chiller Types 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 chiller. The low-temperature generator pump returns the dilute absorbent...
Page 29 - condensate heat exchanger; transfers heat from the hot
24 TRG-TRC011-EN notes period two Absorption Chiller Types to the absorber reduces the flow rate of cooling water required through the absorber. The chiller shown in Figure 27 is steam-fired and includes an additional heat exchanger. This condensate heat exchanger transfers heat from the hot condens...
Page 30 - series flow; cycle, the dilute solution from the absorber is pumped
TRG-TRC011-EN 25 period two Absorption Chiller Types 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. T...
Page 31 - parallel flow; cycle, the dilute solution from the absorber is split
26 TRG-TRC011-EN notes period two Absorption Chiller Types 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 returnin...
Page 32 - , the intermediate solution absorbs
TRG-TRC011-EN 27 period two Absorption Chiller Types notes Direct-Fired Chiller The indirect-fired absorption chillers discussed previously use steam or a hot liquid (such as water) as the energy source. In contrast, the high-temperature generator of a direct-fired absorption chiller uses the heat r...
Page 33 - where it flows through the tubes that are; returns the dilute absorbent solution; to be preheated by the
28 TRG-TRC011-EN notes period two Absorption Chiller Types separate from the absorbent solution. As the refrigerant boils away, the solution becomes concentrated and returns to the absorber. The hot refrigerant vapor produced in the high-temperature generator migrates to the low-temperature generato...
Page 34 - high-temperature generator pump; draws a portion of the intermediate; high-temperature heat
TRG-TRC011-EN 29 period two Absorption Chiller Types 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. This cooler intermediate solution passes through the ...
Page 35 - In the direct-fired absorption chiller shown here, an; auxiliary heating bundle
30 TRG-TRC011-EN notes period two Absorption Chiller Types Chiller/Heater One of the benefits of a direct-fired absorption chiller is that it can be used to provide both cooling and heating. These chillers, therefore, can be installed in systems to supplement, or even replace, primary heating or dom...
Page 36 - cooling only
TRG-TRC011-EN 31 period two Absorption Chiller Types notes Each of these operating modes serves a different load requirement. n In cooling only mode, the absorption chiller operates exactly like the standard chiller offering. Its function is to make cold water. n In heating only mode, the only funct...
Page 38 - Larger physical size.
TRG-TRC011-EN 33 period two Absorption Chiller Types notes While they are presently not available, higher-effect absorption chillers are being studied for commercial use due their potential for higher COPs. Typical COPs for these triple-effect cycles are 1.4 to 1.5. Implementation of these cycles in...
Page 39 - Capacity Control; Equilibrium Chart for Aqueous Lithium Bromide Solutions; period three
34 TRG-TRC011-EN notes period three Capacity Control The primary objective of the chiller capacity control system is to reliably maintain the temperature of the chilled water leaving the evaporator. The control system monitors the temperature of the leaving chilled water, compares it to the setpoint...
Page 40 - and
TRG-TRC011-EN 35 period three Capacity Control notes other words, the combination of solution temperature and concentration determines the temperature at which the refrigerant will boil (vaporize). Varying the temperature at which the refrigerant boils in the evaporator changes the capacity of the a...
Page 41 - In more modern absorption chiller designs,; adjustable-frequency drives
36 TRG-TRC011-EN notes period three Capacity Control In more modern absorption chiller designs, adjustable-frequency drives (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. AFDs have the added be...
Page 42 - Crystallization; crystallization
TRG-TRC011-EN 37 period three Capacity Control notes out of the condition called crystallization—a solidification of the bromide salt. Crystallization will be discussed next. In the past, absorption water chillers would vary the heat input to the generator as the primary means of maintaining the des...
Page 43 - ) as it passes through the heat exchanger. As noted
38 TRG-TRC011-EN notes period three Capacity Control By plotting the single-effect absorption refrigeration cycle on the equilibrium chart, it is apparent that crystallization is most likely to occur in the heat exchanger. At this particular condition, the 65% concentrated solution ( ' ) is cooled t...
Page 44 - Air and other noncondensables leaking into the chiller
TRG-TRC011-EN 39 period three Capacity Control notes As discussed, the point at which crystallization occurs is determined by the temperature and concentration of the concentrated solution inside the heat exchanger. There are generally three possible causes of crystallization in an absorption water ...
Page 49 - Purge System; purge system; is required to remove, or “purge,” the air and other
44 TRG-TRC011-EN notes period three Capacity Control Purge System As presented earlier, the accumulation of air and other noncondensable gases undermines the efficiency and reliability of the absorption chiller. Since absorption chillers operate below atmospheric pressure, regular operation of a pur...
Page 51 - Maintenance Considerations; period four
46 TRG-TRC011-EN notes period four Maintenance Considerations Today, after an absorption chiller is installed and put into operation, it functions without a full-time attendant. In most cases, the chiller starts and stops on a schedule controlled by a building automation system or a simple time cloc...
Page 53 - With the purge unit operating, check the purge tank condensing
48 TRG-TRC011-EN notes period four Maintenance Considerations Most purges are fully automatic and generally require less maintenance than previous-generation manually operated purges. Purge-related maintenance procedures are simple. n Weekly: With the purge unit operating, check the purge tank conde...
Page 56 - corrosion; to achieve and maintain design performance. This
TRG-TRC011-EN 51 period four Maintenance Considerations notes An absorption chiller requires a very deep vacuum to operate efficiently. The introduction of air and other noncondensables into the chiller will adversely affect the chiller ’s performance. In a lithium bromide absorption chiller, where ...
Page 58 - Application Considerations; Cooling-water temperature limitations; period five
TRG-TRC011-EN 53 notes period five Application Considerations Several considerations must be addressed when applying absorption water chillers, including: n Cooling-water temperature limitations n Combination chiller plants n Special considerations for direct-fired chillers n Equipment rating standa...
Page 59 - Cooling-Water Temperature Limitations
54 TRG-TRC011-EN notes period five Application Considerations Cooling-Water Temperature Limitations The temperature of the cooling water significantly impacts the operation of an absorption chiller. As the temperature of the entering-cooling-water decreases, chiller capacity increases. Some absorpti...
Page 60 - Combination Chiller Plants
TRG-TRC011-EN 55 period five Application Considerations notes Combination Chiller Plants Absorption chillers possess two operating characteristics that can noticeably improve overall system efficiency and reduce system energy costs. First, absorption chillers use fossil fuels rather than electricity...
Page 62 - Special Considerations for Direct-Fired Chillers; Combustion air requirements:
TRG-TRC011-EN 57 period five Application Considerations notes Special Considerations for Direct-Fired Chillers The combustion process that occurs in the burner is key to the operation of a direct-fired absorption chiller. It also introduces several additional considerations when applying this type o...
Page 63 - This code does not apply where water is the primary refrigerant.
58 TRG-TRC011-EN notes period five Application Considerations In general, ASHRAE Standard 15-1994, “Safety Code for Mechanical Refrigeration,” does not apply to absorption water chillers due to Section 2.3, which states: This code does not apply where water is the primary refrigerant. Section 8.13.6...
Page 64 - Equipment Rating Standards; system
TRG-TRC011-EN 59 period five Application Considerations notes a refrigerant vapor detector to monitor refrigerant levels in the machinery room. When the detector measures refrigerant levels above those allowable, a building automation system is used to automatically shut down the combustion process....
Page 65 - , dilute solution absorbs heat from the steam or hot water; , where heat transfers from the hot; , causing a pressure drop that reduces the; period six; Review
60 TRG-TRC011-EN notes We will now review the main concepts that were covered in this clinic on absorption water chillers. Period One presented the basic single-effect, absorption refrigeration cycle. In the generator , dilute solution absorbs heat from the steam or hot water flowing through the tub...
Page 68 - Recommended data for a daily log
TRG-TRC011-EN 63 period six Review notes Period Four described general maintenance requirements for absorption water chillers, including: n Recommended data for a daily log n Recommended maintenance for mechanical components, such as the solution and refrigerant pumps, purge, and burner n Recommende...
Page 69 - For more information, refer to the following references:
64 TRG-TRC011-EN notes period six Review For more information, refer to the following references: n Trane product catalogs for absorption water chiller products (Trane literature order numbers ABS-DS-1, ABS-DS-4, ABS-DS-6, and ABS-PRC001-EN) n Absorption Chiller System Design Applications Engineerin...
Page 70 - Quiz
TRG-TRC011-EN 65 Questions for Period 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. 3 What are the two major components on the high-pressure side of the absorption refrigeration...
Page 71 - Questions for Period 3; What is crystallization?; Questions for Period 4; What is the purpose of analyzing the lithium bromide solution?; Questions for Period 5
66 TRG-TRC011-EN Quiz Questions for Period 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 crystallization? 11 What are the most common causes of crystallization in an absorption chiller and how...
Page 73 - Answers
68 TRG-TRC011-EN 1 Refrigerant (distilled water) and absorbent (lithium bromide) 2 $ generator, % condenser, & expansion device, ' evaporator, ( absorber, ) heat exchanger 3 Generator and condenser; evaporator and absorber 4 Below atmospheric pressure 5 Condenser and evaporator 6 To preheat the ...
Page 74 - Glossary
TRG-TRC011-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. In absorption water chillers, the absorbent is commonly lithium bromide. absorber A component of the absorption refrigeration syst...
Page 76 - See
TRG-TRC011-EN 71 Glossary purge A device used to remove air and other noncondensable gases that may leak into the low-pressure absorption chiller. refrigerant A substance used to absorb and transport heat for the purpose of cooling. In a large absorption water chiller, the refrigerant is distilled w...
