Trane TRG-TRC004-EN - Manual

TRG-TRC004-EN iii Contents Introduction ........................................................... 1 period one Compressor Types ............................................... 3 Reciprocating Compressor ...................................... 4 Scroll Compressor .......................................

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. It delivers the refrigerant vapor to the condenser at a pressure and temperature at which the condensing proce...

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). A diagram of the basic vapor-compression refrigeration cycle can be superimposed on a pressure–enthal...

TRG-TRC004-EN 3 notes period one Compressor Types 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. The traditional re...

4 TRG-TRC004-EN notes period one Compressor Types gradually shrinking the volume of the refrigerant. Thus, they are called positive-displacement compressors. In contrast, centrifugal compressors use the principle of dynamic compression , which involves converting energy from one form to another in o...

TRG-TRC004-EN 5 period one Compressor Types 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. When the pressure inside the cylinder exceeds the suction pre...

TRG-TRC004-EN 7 period one Compressor Types 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. The scroll compressor uses two scroll c...

TRG-TRC004-EN 9 period one Compressor Types 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 ag...

10 TRG-TRC004-EN notes period one Compressor Types 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. The refrigerant vapor is drawn into the scrol...

TRG-TRC004-EN 11 period one Compressor Types 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. Only the male rotor i...

12 TRG-TRC004-EN notes period one Compressor Types 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. This action progressiv...

TRG-TRC004-EN 13 period one Compressor Types 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]. Centrifugal Compressor The centrifugal compressor uses the principle of dynamic compression, which i...

14 TRG-TRC004-EN notes period one Compressor Types 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, increas...

16 TRG-TRC004-EN notes period one Compressor Types 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 to8,500 tons [30,000 kW]. In ...

TRG-TRC004-EN 17 period one Compressor Types 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 tha...

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. Capacity control is commonly accomplishe...

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 de...

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 loa...

26 TRG-TRC004-EN notes period two Compressor Capacity Control Slide Valve 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 ...

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. The o...

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. By changing the refrigerant’s angle o...

TRG-TRC004-EN 29 period two Compressor Capacity Control notes Variable 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 Two 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. The airside system responds to changing space ...

TRG-TRC004-EN 33 period three The Compressor in a System notes In a VAV 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...

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 ...

38 TRG-TRC004-EN notes We 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. The first ...

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...

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. 3 What causes the suction valve to open on a reciprocating compressor? 4 True or False: The intake of refrige...

44 TRG-TRC004-EN 1 To 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. 2 Reciprocating, scroll, helical-rotary (or screw), and centrifugal 3 During the intake stroke, t...

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 and Air-Conditioning Engineers centrifugal compressor A type of compressor that uses centrifugal force,...