Compressor Selection

Compressor Selection

The compressor must be selected fot the capacity required at the desired operating conditions in accordance with the manufacturer´s recommendations for the refrigerant to be used. Standard copeland single stage comppresors are approved for aperation with a given refrigerant in one of following operating ranges.

                                                  Evaporating temperature
                                                 _______________________

High Temperature                   45º F. to 0º F. or 55º F. to 0º F.

Medium Temperature             25º F. to -5º F. 

Low Temperature                   0º f. to -40º F.

Extra Low Temperature         -20º F. to -40º F.


Operation at avaporating temperatures above the approved aperating range may overload the compressor motor. Operation at evaporanting temperatures below the approvet operating range is normally not a problem if the compressor motor can be adequately cooled, and discharge temperatures can be kept within allowable limits. Evaporating temperatures below -40º F. are normally beyond the practical lower limit of single stage operation because of compressor inefficiencies and excessive discharge gas temperatures. Because of problems of motor cooling or overloading, some motor-compressors may have approval for operation at limited condensing or evaporating temperatures within a given range, and if so, these limitations will be shown by limited performance curves on the specification sheet.

A give compressor may be approved in two different operating ranges with different refrigerants, for example. high temperature R-12 and low temperature R-502. sence the power requirements for a given displacement with both R-22 and R-502 are somewhat similar, in some cases a compressor may be approved in the same operating range for either of these refrigerants.

Two stage compressors may be approved for evaporating temperatures as low as -80º F., but individual compressor specifications shoould be consulted for the approved operating range. Operation at temperatures below -80º F. is normally beyond the practical efficiency range of copeland two stage compressors, and for lower evaporating temperatures, cancade systems should be employed.

Ccompressors with unloaders have individually established minimun operating evaporating temperatures since motor cooling in more critical with these compressors. As the compressor in unloaded, less refrigerant is circulated through the system, and consequently less return gas is available for motor cooling purposes.

Copeland motor-compressors should never be operated beyond published operating limits without prior approval of the copeland application Engineering Department.