Comparison of performance characteristics of SCR and ECM controlled series fan powered terminal units

Abstract

Airflow, efficiency, power, and power quality characteristics were evaluated for two variable air volume series fan powered terminal units. The power and power quality data included real power, power/airflow, apparent power, harmonic frequencies, and total harmonic distortion. Each unit had the same sized primary air inlet and were provided by the same manufacturer. One unit had a motor controlled by a silicon controlled rectifier and the other had an electronically commutated motor. Data were collected at a fixed downstream static pressure and a range of upstream static pressures, primary inlet damper positions, and input controller voltages. Both controllers maintained a nearly constant fan airflow as the primary air was varied. Fan/motor efficiencies were low (below 35%) and increased with fan static pressures. The electronically commutated motor unit had efficiencies as much as four times higher than the silicon controlled rectifier controlled unit which was reflected in much lower power draws. The electronically commuted fan/motor unit had the lowest apparent power at airflows below approximately 1000 ft3/min (0.47 m3/s). For both units, the total power harmonic distortion was less than 1%. The performance data indicated a major advantage of units with electronically commutated motors.