Trane TRG-TRC014-EN manual Forward-CurvedCentrifugal Fan, Fan Modulation, period four

period four

Fan Modulation

notes

Forward-Curved Centrifugal Fan

input power

B

3.15 in. H2O [784.6 Pa]

2.7 in. H2O	A
[672.5 Pa]

		1
		,
		0
		0
		0
		r
		p
		m
18,000 cfm
	24,000 cfm		Figure 76
[8.5 m3/s]	[11.3 m3/s]

This “riding the fan curve” method of modulation can be used with any centrifugal fan. However, it is most energy efficient when applied to forward- curved (FC) fans. The configuration of the input power curves of the

FC fan are such that input power requirements drop as the fan operating point moves upward along the constant-speed performance curve.

“Riding the fan curve” can be used successfully when the airflow modulation range for the system is small. On the other hand, if the system is required to modulate over a wide range of airflows, the increased static pressure experienced at reduced airflows may overpressurize the VAV terminals, resulting in greater-than-desired space airflow and noise problems. Additionally, if the fan enters an unstable area of operation at this high static pressure, fan vibration, called “surge”, and severe air pulsation within the duct system, may result. This may lead to objectionable noise levels and potentially a mechanical fan failure.

TRG-TRC014-EN 55