Trane TRG-TRC004-EN manual DSDFLW\9HUVXV6XFWLRQ7HPSHUDWXUH

period two

Compressor Capacity Control

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VXFWLRQ￿WHPSHUDWXUH Figure 31

A plot of compressor capacity versus suction temperature (assuming a constant condensing temperature) reveals that the capacity of the compressor increases as the suction temperature increases. As the suction temperature, and, therefore, the suction pressure, increases, the refrigerant vapor becomes denser. A greater quantity of refrigerant can be compressed in a given compression cycle and the capacity of the compressor is higher.

For an example nominal-30-ton [105 kW] reciprocating compressor that has six cylinders, Figure 31 shows the capacity produced by the various stages of unloading. Four of the six cylinders are equipped with unloaders, and two cylinders are unloaded as a pair. The compressor, therefore, can operate with all six cylinders loaded, with four cylinders loaded, with only two cylinders loaded, or it can shut off. Again, these capacity curves assume the compressor is operating at a constant condensing (discharge) pressure.

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