Trane TRG-TRC004-EN manual 5HYLHZ²3HULRG7ZR

period four

Review

notes

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Figure 53

Period Two reviewed various methods of varying compressor capacity. Reciprocating compressors typically use cylinder unloaders that match the compressor capacity to the evaporator load by deactivating piston–cylinder pairs.

Refrigeration systems using scroll compressors generally unload by using multiple compressors, cycling them on and off as needed to satisfy the evaporator load.

A common method of unloading a helical-rotary compressor is to use a slide valve that is an integral part of the compressor housing. By changing the position of the slide valve along the compressor rotors, the volume of refrigerant vapor being delivered by the compressor can be controlled to match the evaporator load.

Finally, centrifugal compressors generally use inlet vanes to “preswirl” the refrigerant before it enters the impeller, lessening the ability of the impeller to take in the refrigerant. As a result, the compressor’s refrigerant pumping capacity decreases to balance with the evaporator load.

Alternatively, the capacity of any of these types of compressors can be controlled by varying the rotational speed of the compressor motor. It is most often applied, however, to centrifugal compressors.

TRG-TRC004-EN 39