Trane Fan manual Application Considerations

Application Considerations

The control static pressure can then be expressed as a percent of peak static pressure and plotted. The system modulation curve is described by the curve on the modulation overlay that passes through the design point when the axis is placed on the control static pressure point.

The minimum inlet vane cfm can easily be determined after the system modulation has been established. It will be one of two things, either a) the point where the system modulation curve intersects the surge line, or

b)40 percent wocfm, whichever is greater. Forty percent wocfm is the minimum point a Q fan with inlet vanes can modulate, due to inherent instability that results when the vanes close to a certain angle.

A plot of part load cfm versus brake horsepower can also be made after the system modulation curve is established. At each intersection of the system modulation curve with a cfm-sp curve for a certain inlet vane opening, a vertical line is traced to the appropriate bhp-cfm curve. At each intersection of a bhp-cfm curve, a horizontal line is traced to the scale of percent brake horsepower.This will lead to a percent wocfm versus percent peak bhp plot.

The design rpm and bhp need to be corrected to account for performance losses due to inlet vanes being in the air stream. A correction of one percent to the rpm and three percent to the bhp is made in order to get to design conditions with the inlet vanes fully open.

Part load fan power consumption with inlet vanes can be determined by entering Figure A-6 at the desired percent wide open cfm. (Wide open cfm is found on the fan curve by following the fan rpm to the right until it intersects the 0” static pressure axis.)

Figure A-6 – Inlet Vane Performance

On Figure A-6, plot a system curve from the control static pressure through the point of operation defined as a calculated percent wide open cfm. Read vertically upward from the 25, 50 and 75 percent intersections to determine the percent bhp at part load.

Intermediate operating points are found by extrapolation. Inlet vanes increase Q fan sound levels. SeeTable A-5.

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