Trane TRG-TRC014-EN manual period four, Fan Modulation, Fan Performance Curve, VAV Systems

period four

Fan Modulation

notes

VAV Systems

period four

Fan Modulation

Figure 71

To accommodate the variable-volume requirements imposed by a VAV system, the system supply fan must be selected and controlled in such a manner that it is capable of modulating over the required airflow range without entering an unstable area of operation.

First, certain VAV system basics should be reviewed, including:

nThe fan performance curve

nThe system resistance curve

nThe fan modulation curve

Fan Performance Curve

static pressure

2.7 in. H2O

[672.5 Pa]

airflow	24,000 cfm	Figure 72
	[11.3 m3/s]

Fan Performance Curve

The fan performance curve of a centrifugal fan is a plot of the airflow capacity at a given speed (rpm) versus the static pressure it generates. While a centrifugal fan produces both static and velocity pressures, it is traditional to

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