PREDICTING VARIABLE-SPEED FAN PERFORMANCE FROM MOTOR AND IMPELLER CHARACTERISTICS .2. USING LIMITED MOTOR DATA

Computerized procedures were developed for selecting and matching moto rs and impellers for agricultural ventilation fans. Designers of varia ble-speed, agricultural ventilation fans may sometimes have only limit ed performance information on commercially available motors, especiall y for voltage-controlled, permanent-split capacitor motors. Theoretica l performance of three-phase induction motors was applied to single-ph ase, permanent-split capacitor motors to develop equations for estimat ing motor performance at low speeds. They developed a simple estimatin g procedure to predict variable-speed fan performance, requiring only motor efficiency, speed, and mechanical power at peak efficiency, and starting torque (or motor speed at breakdown torque). This procedure e stimates motor efficiency, triac-generated control voltage, fan airflo w rate, and ventilating efficiency ratio over the entire speed range. The development of equations from theoretical relationships along with simplifying assumptions is presented. Predicted results agreed satisf actorily with laboratory measurements.