VARIABLE-SPEED FAN PERFORMANCE WITH SELECTED SINGLE-PHASE AND 3-PHASEMOTORS

A variable-speed fan system was tested with four combinations of two m otor types and two speed control methods. The frequency control method and the voltage control method were each applied to a single-phase, p ermanent-split-capacitor motor and a three-phase motor. The frequency- controlled, three-phase motor was superior to the voltage-controlled s ingle-phase motor at reduced speeds in terms of ventilating efficiency ratio (VER), motor efficiency, and fan controllability. The VER, moto r efficiency, and power factor were significantly higher for the frequ ency-controlled, three-phase motor as compared to the frequency-contro lled, single-phase motor except at full speed. Good fan controllabilit y was obtained with frequency control for both motors. The VER and mot or efficiency were the lowest for the voltage-controlled, three-phase motor at all speeds. Economic analyses of annual fan operation with as sumed load factors were discussed.