Trane TRG-TRC004-EN Air Compressor User Manual


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24 TRG-TRC004-EN
notes
period two
Compressor Capacity Control
Cycling On and Off
Scroll compressors do not have valves or unloaders. A piece of equipment that
uses scroll compressors generally unloads by using multiple compressors and
turning them on and off, as needed, to satisfy the evaporator load.
Cycling multiple scroll compressors is very similar to the use of cylinder
unloaders on a single reciprocating compressor. As an example, a large 40-ton
[140.6-kW] reciprocating compressor may have eight cylinders with unloaders
on six of them, allowing it to unload in equal steps of 10 tons [35.2 kW] each,
with a minimum nominal capacity of 10 tons [35.2 kW].
A similar 40-ton [140.6-kW] unit using scroll compressors would include four
separate 10-ton [35.2-kW] scroll compressors. Just as the reciprocating
compressor unloads in equal intervals by unloading a pair of cylinders, the
scroll compressor unit unloads in the same 10-ton [35.2-kW] intervals by
shutting off individual compressors.
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