Centrifugal compressors are essentially high-speed machines and best suited for steam-turbine drives. Because they are designed for the same high speed as the turbine, they may be directly connected. Where high-pressure steam is generated, the turbine can act as a reducing valve, and the low-pressure steam that leaves the turbine can be used for heating and other purposes. In smaller sizes, a great many applications are driven by electric motors and equipped with gear-type speed increasers. Centrifugal compressors are used with low-pressure refrigerants, and both evaporator and condenser usually work below atmospheric pressure.
Compression of the refrigerant is accomplished by means of centrifugal force. Because of this, centrifugal compressors are best suited for large refrigerant volumes and low-pressure differentials. They are well-suited to low-temperature refrigerating cycles, especially those using petroleum or halogenated hydrocarbons as a refrigerant.
Centrifugal-compressor installations are economically advantageous where steam-turbine drive is permitted, since the installation and labor required for such an installation is relatively small compared to that required for a comparable gas-engine–driven compressor plant. This is mainly because of the compactness and lightness of the unit compared to the amount of horsepower involved. In addition, a centrifugal compressor will occupy only a fraction of the space ordinarily required for refrigerating equipment. Refrigerating units of the centrifugal type are available in various sizes varying from 100 to 2500 tons capacity, and are manufactured for use with electric motors, steam turbines, or internal-combustion engines.