System Balance and Refrigerant

System Balance

If the compressor or condensing unit selected for a given application is to satisfactorily handle the refrigeration load, it must have sufficient capacity. However, over capacity can be equally as unsatisfactory as under capacity, and care must be taken to see that the compressor and evaporator balance at the desired operating conditions. Checking the proposed system operation by means of a compressor-evaporator-condenser balance chart as describet in selection 16 is recommended.

If fluctuations in the refrigeration load are to be expected, which could result in compressor operation at excessively low suction pressures, then some means of capacity control must be provided to maintain acceptable evaporating temperatures. If compressors with unloaders are not available or suitable, and if the load cannot be adequately handled by cycling the compressor. a hot gas bypass circuit may be required.



Refrigerant

Copeland compressors are primarily designed for operation with refrigerants 12, 22, and 502. Operation with other refrigerants in cascade systems may be satisfactory if the proper motor and displacement combination is selected, adequate lubrication can be maintained, and if adequate compressor protection is provided. All applications with refrigerants other than R-12, R-22 and       R-502 must be approved by the copeland aplication Engineering Departament.

R-22 is highly recommended for all single stage low temperature applications, and particularly where evaporating temperatures of -20 F. and below may be encountered. Because of the undesirable high discharge temperatures of R-22 when operated at high compression rations, R-22 should not be used in single stage low temperature compressors 5 HP and larger.

Different expansion valves are requiered for each refrigerant, so the refrigerants are not interchageable in a given system, and should never be mixed, If for some reason it is desirable to change from one refrigerant to another in an existing system by changing expansion valves and control settings providing the existing piping sizes and component working pressures are compatible. In some cases the existing motor-compressor may be satisfactory --for example, in converting from R-22 to R-502. If the conversion will result in higher power requirements as is the case in changing from R-12 to R-502. then it may also be necessary to change the motor-compressor.

The refrigerant charge should be held to the minimum required for satisfactory operation, since an abnormally high charge will create potential problems of liquid refrigerant control.