9.8Refrigeration Components and Evaporative CoolersRefrigeration CompressorsA refrigeration compressor is the heart of a vapor compression system. It raises the pressure of refrigerantso that it can be condensed into liquid, throttled, and evaporated into vapor to produce the refrigerationeffect. It also provides the motive force to circulate the refrigerant through condenser, expansion valve,and evaporator.According to the compression process, refrigeration compressors can be divided into positive displacement and nonpositive displacement compressors. A positive displacement compressor increases thepressure of the refrigerant by reducing the internal volume of the compression chamber. Reciprocating,scroll, rotary, and screw compressors are all positive displacement compressors. The centrifugal compressor is the only type of nonpositive displacement refrigeration compressor widely used in refrigerationsystems today.