Predicting variable-speed fan performance from motor and impeller characteristics. I. Using complete motor data.
Computerized procedures were developed for selecting and matching motors and impellers for agricultural ventilation fans. Designers of variable-speed, agricultural ventilation fans may sometimes have only limited performance information on commercially available motors, especially for voltage-controlled, permanent-split capacitor motors. Theoretical performance of three-phase induction motors was applied to single-phase, permanent-split capacitor motors to develop equations for estimating motor performance at low speeds. They developed a simple estimating 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 estimates motor efficiency, triac-generated control voltage, fan airflow 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 satisfactorily with laboratory measurements.