Instruction/ maintenance manual of the product TRG-TRC004-EN Trane
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Air Conditioning Clinic Refrigeration Compressors One of the Fundamental Series TRG-TRC004-EN.
NO POST AGE NECESSARY IF MAILED IN THE UNITED ST A TES BUSINESS REPL Y MAIL FIRST -CLASS MAIL PERMIT NO. 1 1 LA CROSSE, WI POST AGE WILL BE P AID BY THE TRANE COMP ANY Attn: Applications Engineering 3600 Pammel Creek Road La Crosse WI 54601-9985 NO POST AGE NECESSARY IF MAILED IN THE UNITED ST A TES BUSINESS REPL Y MAIL FIRST -CLASS MAIL PERMIT NO.
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Refrigeration Compressors One of the Fundamental Series A publication of The T rane Company— W orldwide Applied Systems Group.
Preface © 2000 American Standard Inc. All rights reserved TRG-TRC004-EN ii The T rane 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.
TRG-TRC004-EN iii Contents Introduction ........................................................... 1 period one Compressor Types ............................................... 3 Reciprocating Compressor ...................................... 4 Scroll Compressor .
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TRG-TRC004-EN 1 notes Introduction The purpose of the compressor in a refrigeration system is to raise the pressure of the refrigerant vapor from evaporator pressure to condensing pressure.
2 TRG-TRC004-EN notes Introduction The pressure – enthalpy (P – h ) chart plots the properties of a refrigerant: refrigerant pressure (vertical axis) versus enthalpy , or heat content (horizontal axis).
TRG-TRC004-EN 3 notes period one Compressor T ypes This period is devoted to the discussion of the different types of compressors. There are primarily four types of compressors used in the air -conditioning industry: reciprocating, scroll, helical-rotary (or screw), and centrifugal.
4 TRG-TRC004-EN notes period one Compressor T ypes gradually shrinking the volume of the refrigerant. Thus, they are called positive-displacement compressors.
TRG-TRC004-EN 5 period one Compressor T ypes notes During the compression stroke , the piston reverses its direction and travels toward the discharge valve, compressing the refrigerant vapor and increasing the pressure within the cylinder .
6 TRG-TRC004-EN notes period one Compressor T ypes In the reciprocating compressor shown, the refrigerant vapor from the suction line enters the compressor through the suction opening. It then passes around and through the motor , cooling the motor , before it enters the cylinder to be compressed.
TRG-TRC004-EN 7 period one Compressor T ypes notes Scroll Compressor Similar to the reciprocating compressor , the scroll compressor works on the principle of trapping the refrigerant vapor and compressing it by gradually shrinking the volume of the refrigerant.
8 TRG-TRC004-EN notes period one Compressor T ypes The center of the scroll journal bearing and the center of the motor shaft are offset. This offset imparts an orbiting motion to the driven scroll. Rotation of the motor shaft causes the scroll to orbit — not rotate — about the shaft center .
TRG-TRC004-EN 9 period one Compressor T ypes notes During the first full revolution of the shaft, or the intake phase , the edges of the scrolls separate, allowing the refrigerant vapor to enter the space between the two scrolls. By the completion of first revolution, the edges of the scrolls meet again, forming two closed pockets of refrigerant.
10 TRG-TRC004-EN notes period one Compressor T ypes In this example scroll compressor , refrigerant vapor enters through the suction opening. The refrigerant then passes through a gap in the motor , cooling the motor , before entering the compressor housing.
TRG-TRC004-EN 11 period one Compressor T ypes notes The rotors are meshed and fit, with very close tolerances, within the compressor housing. The gap between the two rotors is sealed with oil, preventing the compressed refrigerant vapor from escaping through the mating surfaces.
12 TRG-TRC004-EN notes period one Compressor T ypes Viewing the compressor from the opposite side shows that continued rotation of the meshed rotor lobes drives the trapped refrigerant vapor (to the right), toward the discharge end of the compressor , ahead of the meshing point.
TRG-TRC004-EN 13 period one Compressor T ypes notes In the air -conditioning industry , helical-rotary compressors are most commonly used in water chillers ranging from 70 to 450 tons [200 to 1,500 kW].
14 TRG-TRC004-EN notes period one Compressor T ypes The center , or eye, of the impeller is fitted with blades that draw refrigerant vapor into radial passages that are internal to the impeller body . The rotation of the impeller causes the refrigerant vapor to accelerate within these passages, increasing its velocity and kinetic energy .
TRG-TRC004-EN 15 period one Compressor T ypes notes This chart plots the conversion of energy that takes place as the refrigerant passes through the centrifugal compressor . In the radial passages of the rotating impeller , the refrigerant vapor accelerates, increasing its velocity and kinetic energy .
16 TRG-TRC004-EN notes period one Compressor T ypes In the air -conditioning industry , centrifugal compressors are most commonly used in prefabricated water chillers ranging from 100 to 3,000 tons [350 to 10,500 kW]. They are also used in field-assembled water chillers up to 8,500 tons [30,000 kW].
TRG-TRC004-EN 17 period one Compressor T ypes notes A hermetic compressor , on the other hand, seals the motor within the compressor housing. This motor is cooled by the refrigerant, either by refrigerant vapor that is being drawn into the compressor from the suction line or by liquid refrigerant that is being drawn from the liquid line.
18 TRG-TRC004-EN notes The capacity of a compressor is defined by the volume of evaporated refrigerant that can be compressed within a given time period. The compressor needs a method of capacity control in order to match the ever -changing load on the system.
TRG-TRC004-EN 19 period two Compressor Capacity Control notes Cylinder Unloaders Most large reciprocating compressors (above 10 tons [35 kW]) are fitted with cylinder unloaders that are used to match the compressor ’ s refrigerant- pumping capacity with the falling evaporator load, by progressively deactivating piston – cylinder pairs.
20 TRG-TRC004-EN notes period two Compressor Capacity Control In response to an increasing load, the controller sends a signal to close the solenoid valve. This closes the port that allows the pressurized refrigerant vapor to travel to the top of the unloader valve.
TRG-TRC004-EN 21 period two Compressor Capacity Control notes A plot of compressor capacity versus suction temperature (assuming a constant condensing temperature) reveals that the capacity of the compressor increases as the suction temperature increases.
22 TRG-TRC004-EN notes period two Compressor Capacity Control At design conditions, the capacities of the evaporator coil and compressor balance ( A ) at a suction temperature of 45 ° F [7.
TRG-TRC004-EN 23 period two Compressor Capacity Control notes In the case of comfort-cooling applications, however , the load generally changes slowly in small intervals. For example, assume that the load decreases from 28 tons [98.5 kW] ( B ) to 25 tons [88 kW].
24 TRG-TRC004-EN notes period two Compressor Capacity Control Cycling On and Off Scroll compressors do not have valves or unloaders. A piece of equipment that uses scroll compressors generally unloads by using multiple compressors and turning them on and off, as needed, to satisfy the evaporator load.
TRG-TRC004-EN 25 period two Compressor Capacity Control notes At design conditions, the capacities of the evaporator and this four -compressor unit balance at a suction temperature of 43 ° F [6.
26 TRG-TRC004-EN notes period two Compressor Capacity Control Slide V alve The helical-rotary compressor used as the example in this clinic is unloaded using a slide valve that is an integral part of the compressor housing. Other helical-rotary compressor designs may use a variety of methods to vary capacity .
TRG-TRC004-EN 27 period two Compressor Capacity Control notes At full load, the slide valve is closed. The compressor pumps its maximum volume of refrigerant, discharging it through the discharge port. As the load on the compressor decreases, the slide valve modulates toward the open position.
28 TRG-TRC004-EN notes period two Compressor Capacity Control methods of capacity control, many of them function in a manner similar to the inlet vanes presented in this section of the clinic. Inlet vanes “ preswirl ” the refrigerant before it enters the impeller .
TRG-TRC004-EN 29 period two Compressor Capacity Control notes V ariable Speed Alternatively , the capacity of a compressor can be controlled by varying the rotational speed of the compressor motor . This is accomplished using a device called an adjustable-frequency drive (AFD) or variable-speed drive .
30 TRG-TRC004-EN notes period three The Compressor in a System Period T wo presented several methods used to control the capacity of a compressor . This next section considers the entire system in order to determine how the capacity of the compressor is controlled to maintain desired space conditions.
TRG-TRC004-EN 31 period three The Compressor in a System notes from the air used for space conditioning. In contrast, the refrigerant inside the evaporator of a direct-expansion (DX) system absorbs heat directly from the air used for space conditioning.
32 TRG-TRC004-EN notes period three The Compressor in a System As mentioned previously , a V A V system varies the quantity of air supplied to the space in order to satisfy the load.
TRG-TRC004-EN 33 period three The Compressor in a System notes In a V A V chilled water system (shown in Figure 46), the capacity of the chilled- water coil is controlled to maintain the desired supply air temperature. By sensing the supply air temperature, a controller varies the flow of water through the coil by modulating the valve.
34 TRG-TRC004-EN notes period three The Compressor in a System suction temperature for a specific application depends on the system operating conditions and the evaporator design.) Evaporator freeze protection in a chilled-water application is accomplished by sensing the temperature of the water in the evaporator .
TRG-TRC004-EN 35 period three The Compressor in a System notes Hot gas bypass may be another solution for preventing evaporator frosting in DX applications. Hot gas bypass diverts hot, high-pressure refrigerant vapor from the discharge line to the low-pressure side of the refrigeration system.
36 TRG-TRC004-EN notes period three The Compressor in a System The second method bypasses refrigerant vapor from the compressor discharge line to the suction line. This method requires the service of an additional expansion valve, called a liquid injection valve.
TRG-TRC004-EN 37 period three The Compressor in a System notes suction temperature falls, and coil frosting or chiller freezing may occur . Since the hot-gas-bypass valve is sized to pass a given quan.
38 TRG-TRC004-EN notes W e will now review the main concepts that were covered in this clinic on refrigeration compressors. Period One introduced the four types of compressors commonly used in air - conditioning applications: reciprocating, scroll, helical-rotary (or screw), and centrifugal.
TRG-TRC004-EN 39 period four Review notes Period T wo reviewed various methods of varying compressor capacity . Reciprocating compressors typically use cylinder unloaders that match the compressor capacity to the evaporator load by deactivating piston – cylinder pairs.
40 TRG-TRC004-EN notes period four Review Period Three considered the entire system and discussed how the capacity of the compressor is controlled to maintain desired space conditions. In a constant-volume DX system, in order to respond to changing loads, the capacity of the compressor is controlled by directly sensing space temperature.
TRG-TRC004-EN 41 period four Review notes For more information, refer to the following references: ■ T rane Air Conditioning Manual ■ T rane Reciprocating Refrigeration Manual ■ Helical-Rotary W.
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TRG-TRC004-EN 43 Questions for Period 1 1 What is the purpose of the compressor in a refrigeration system? 2 List the four primary types of compressors used in air -conditioning applications.
44 TRG-TRC004-EN 1 T o elevate the pressure, and, therefore, the temperature, of the refrigerant vapor high enough that it can reject heat to air , or some other fluid, at normally available temperatures.
TRG-TRC004-EN 45 adjustable-frequency drive (AFD) A device used to vary the capacity of a compressor by varying the speed of the compressor motor . ASHRAE American Society of Heating, Refrigerating an.
46 TRG-TRC004-EN Glossary evaporator A 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 A component of the refrigeration system used to reduce the pressure and temperature of the refrigerant to the evaporator conditions.
TRG-TRC004-EN 47 Glossary reciprocating compressor A type of compressor that uses a piston that travels up and down inside a cylinder to compress the refrigerant vapor . refrigerant A substance used to absorb and transport heat for the purpose of cooling.
The T rane Company Worldwide Applied Systems Group 3600 Pammel Creek Road La Crosse, WI 54601-7599 www .trane.com An American Standard Company Literature Order Number TRG-TRC004-EN File Number E/A V-F.
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