Refrigerating Systems. Compressors

In refrigerating cycle the compressor has two main functions within the cooling cycle. One function for pumping of refrigerant vapour at the outlet of the evaporator to the necessary temperature and pressure can be saved in evaporator. The second function is to increase the pressure of the refrigerant vapor through the compression process, and simultaneously increasing the temperature of the refrigerant vapor. This change in pressure superheated refrigerant passes through the system.

Refrigeration compressors, which are known as the heart of a vapor-compression cooling system can be divided into two main categories:

Displacement compressors and
Dynamic compressors.

Note that both the volume and dynamic compressors can be hermetic, semi-hermetic, or open type.

The compressor of both pumps refrigerant around the circuit and produces the necessary substantial increase in the pressure of the refrigerant. Refrigerant selected operating temperature range required for heat pumping, as a rule, lead to the need for a compressor to ensure a high differential pressure at a moderate speed flow, and is most often met on a piston compressor using a reciprocating piston. Other types of piston compressor use rotating vanes or cylinders or interinclusion screws to move the refrigerant. In some large applications, or centrifugal turbocompressors are not piston machines, but also to accelerate the vaporous as it passes through the compressor casing. These different types of compressors are illustrated in Fig. 3.2.

On the market there are many different types of compressors are available, in terms of body type and compression system. Here are a few options assessment the most common types (DETR, 1999):

Piston-type compressors, piston machines available for each application. The effectiveness of the valve system is greatly improved on many of the larger models. Capacity control is usually by handling cylinders (method that allows to reduce energy consumption almost in line with the capacity).

Scroll compressors rotary positive displacement machines with constant volume ratio. They have good efficiency for air conditioning and high temperature refrigeration units. They are only available for commercial applications, and typically do not have the built-in power control.

Screw compressors are available in large commercial and industrial size and are generally fixed volume fraction machines. Selection of the compressor with the wrong volume ratio can lead to a significant reduction in effectiveness. Partial load is achieved valve or valve discharge. Both types provide a greater reduction in the effectiveness of the load compared with reciprocating capacity management systems.

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