Trane TRG-TRC014-EN manual Fan Modulation Comparisons, period four

period four

Fan Modulation

notes

In response to reduced airflow and rising system static pressure, the variable- pitch vaneaxial fan responds similarly to a centrifugal fan with either inlet-vane or variable-speed capacity control.

By changing the angle of the fan blades, the performance curve for the fan shifts downward, and the airflow and resulting pressure decrease until the operating point (B) balances along the fan modulation curve.

Fan Modulation Comparisons

	100			BI fan with
	90			discharge
	80			dampers
power	70	AF fan with
	60	inlet vanes							FC fan with
% design	50	FC fan with
									inlet vanes
	40	discharge					fan-speed
	30	dampers
	20						control
					variable-pitch
	10
					vaneaxial
	0
		10	20	30	40	50	60	70	80	90	100

% design airflow Figure 89

These curves describe the performance characteristics of each fan modulation method, in terms of the fan power required versus the percent of design airflow. Realize that these are generalized curves based on an arbitrary set of test conditions.

On a generalized basis, the forward-curved (FC) centrifugal fan with inlet vanes, the variable-pitch vaneaxial fan, and fan speed control are similar in performance.

To obtain a more accurate comparison for specific operating conditions, a life- cycle cost analysis should be performed.

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