Trane TRG-TRC004-EN manual 9DULDEOH$LU9ROXPH6\VWHP, KLOOHGDWHU6\VWHP

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The Compressor in a System

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Figure 45

As mentioned previously, a VAV system varies the quantity of air supplied to the space in order to satisfy the load. The supply temperature is held constant in this system.

In a VAV DX system, the capacity of the compressor is controlled by sensing the temperature of the air being supplied to the system. The compressor is loaded or unloaded based on how close the actual supply air temperature is to the set point.

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In contrast to the DX system examples shown previously, a chilled-water system responds to changing space loads by controlling the capacity of the chilled-water cooling coil. Although there are various methods of controlling the capacity of this coil, this discussion will assume the use of a modulating water valve.

32 TRG-TRC004-EN