TABLE OF CONTENTS The main types of compressors used in industrial refrigeration are screw, reciprocating, centrifugal, and rotary vane. Another type that is manufactured in large numbers is the scroll compressor, but so far these compressors are not available in the size normally encountered in industrial refrigeration. Rotary-vane compressors are still in use as low-stage compressors, but very few new ones are installed.
Centrifugal compressors have been standard in large-capacity chemical and process industry plants where they are driven by electric motors or by steam or gas turbines. Centrifugal compressors are also widely used for chilling water in air-conditioning applications. Manufacturers use such refrigerants as R-123 and R-134a in these packages. After condensing the longer list of compressor types, the two that remain, and the ones that will be addressed in this book, are reciprocating and screw compressors. This chapter focuses on reciprocating compressors, while Chapter 5 concentrates on screw compressors.
Two styles of construction of compressors are open and hermetically sealed. In the open-type compressor, as in Figure 4.1, the shaft extends out of the compressor and is connected externally to the electric motor which drives the compressor. In the hermetically-sealed motor-compressor unit, the entire assembly is encapsulated and only the refrigerant lines and electrical connections, and no rotating shaft, penetrate the housing. These hermetically sealed units are always used for domestic refrigerators, window-type air conditioners, and other small appliances. They are expected to run for decades with no leaks of refrigerant.
