The main types of compressors used are: reciprocating, centrifugal, screw, vane and scroll. The choice of type of compressor depends essentially on the capacity of the plant, which can be divided in terms of vaporization temperature and the refrigerant used in: small capacity (<2,5 TR), medium capacity (between 2,5 and 75 TR) and large capacity (> 75 TR). TR stands for refrigeration ton, an expression commonly used in refrigeration to translate the energy needed to liquefy one ton of ice in 24 hours (1TR = 3.5 kw).
According to the characteristics of the compression process, compressors used in refrigeration can be classified as: positive displacement machines or flow machines. The positive displacement compressor increases the pressure of the refrigerant vapor by reducing the internal volume of a chamber by means of an applied mechanical force. Reciprocating, screw, vane and scroll compressors are positive displacement. The only compressor classified as
flow in cooling systems is the centrifugal. In this type of compressor the increase in pressure is mainly due to the conversion of dynamic pressure to static pressure.
Depending on the construction design, the compressors can be classified as: hermetic, semi-hermetic and open. In the hermetic compressor, both the compressor itself and the drive motor are housed inside a housing, presenting as input and output access only the electrical connections of the motor. This type of compressor operates exclusively with halogenated refrigerants and the refrigerant vapor comes into contact with the engine winding, cooling it.
They are generally used in domestic refrigerators and air conditioners with powers of the order of 30kW.
