Trane TRG-TRC004-EN manual FOLQJ2QDQG2II, FOLQJ6FUROO&RPSUHVVRUV, Cycling On and Off

period two

Compressor Capacity Control

notes

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Figure 34

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.

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Figure 35

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.

24 TRG-TRC004-EN