Refrigeration compressors can be classified in the following areas:
Number of cylinders
Location of the driving force of the engine or
The compression method can be piston centrifugal or Rotary. The location of the power source also classifies compressors. Independent compressors driven by a belt. Semi-hermetic compressors have a direct drive motor and the compressor in separate buildings. Hermetic compressor direct drive from engine and compressor in one housing.
Piston units have the piston in the cylinder. Piston acts as a pump to increase the pressure of the refrigerant with the low side the high side of the system. Piston compressor can have twelve or more cylinders (see Fig. 9-1).
The most often used piston compressor is made for the refrigerants R-22 and R-134a.
They are intended for heating, ventilation and Air conditioning and process cooling. The most practical of refrigerants used today, R-134a and R-22. However, R-134a is gaining in acceptance, in connection with the CFC rules worldwide. In fact, in some countries only accept R-134a today. Other environmentally acceptable refrigerants R-404A and R-507. They are designed for low and medium temperatures. R-470C average temperatures and air-conditioning. Recently, R-410Ahas has gained recognition as an environmentally acceptable substitute for R-22, but only for residential and small equipment. R-410A is not a drop-in refrigerant R-22.
There are three types of piston compressors: open the disk, hermetic and semi-hermetic.
Two methods for the control of power are, as a rule, used in reciprocating compressors used in commercial air-conditioning systems. Both methods employ mechanical handling cylinders through an open intake valve.
The most common method of capacity control uses an internal few steps valve. This applies compressor oil pressure or high side of the refrigerant pressure bellows or a piston, which operates the station.
The second method of capacity control uses external electromagnetic valve on each cylinder. Solenoid valve allows the compressor oil or high side refrigerant go to the station.
Acentrifugal compressor, mainly, fan or blower, that builds the refrigerant pressure, forcing gas through a funnel-shaped opening at high speed (see Fig. 9-2).
Compressor capacity is controlled when the blades are opened and closed. These blades to adjust the amount of refrigerant allowed to enter the fan or turbine (see Fig. 9-3). When the blades to limit the flow of the refrigerant, the turbine can not do it full cost of work on the refrigerant. Thus, its capabilities are limited. Most of centrifugal machines can be limited to 10 to 25% capacity with the help of this method. Some of them would work at almost zero potential. However, another method, though less common, to control the motor speed, rotating turbines.