Types of compressors

[Break7]

Hi I have another probably unimportant question but I just have to know! Small condensing units come in low temp, mid or high temp. What is it about the compressor that is different? Is it compression ratio or clearance volume?

[US Iceman]

The basic explanation I can provide is that the various compressors are configured by HP (or kW) power input for a range of compressor displacements.

A high temperature compressor might have a smaller displacement with a larger motor. A low temperature compressor might have a larger displacement and a smaller motor.

For whatever the compressor has the ability to produce for cooling capacity, the condenser is then sized to handle this range of heat rejection.

[wambat]

The hp required for the different mass flow rates at the different temperatures for the same refrigerent because the densities per lb are different.

[Break7]

Thanks for your replies and the benefit of your years of experience!

[NoNickName]

Exactly true. A high temperature compressor has a comparably lower displacement than a low temperature compressor, because the refrigerant density at suction is higher when evaporating temperature is higher, and vicerversa.
The pressure lift is greater for a low temperature compressor (or condensing unit) and the net result is a higher discharge temperature for the same final condensing pressure.