Compressor can be divided into volumetric compressor and velocity compressor according to its principle [3]. Volume type is divided into: reciprocating compressor, rotary compressor; Velocity compressor is divided into: axial compressor, centrifugal compressor and mixed flow compressor.  

Now the household refrigerator and air conditioner compressor are volume type, which can be divided into reciprocating and rotating. Reciprocating compressor is the use of piston, crank, connecting rod mechanism or piston, crank, sliding tube mechanism, rotary use is more than rolling rotor compressor. in the commercial air conditioning, and more are centrifugal, vortex, screw.  

According to the scope of application can be divided into low back pressure type, middle back pressure type, high back pressure type. Low back pressure type (evaporation temperature -35 ~ -15 ℃), generally used in household refrigerators, food freezers, etc. Medium back pressure type (evaporation temperature -20 ~ 0 ℃), generally used for soda fountains, milk freezers, etc. High back pressure type (evaporation temperature -5 ~ 15 ℃), generally used in room air conditioners, dehumidifiers, heat pumps, etc