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TRG-TRC004-EN 21
period two
Compressor Capacity Control
notes
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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Figure 31