CH-24-C034 - Laboratory Evaluation and Potential Energy Savings of High-efficiency Motor and Drive Systems for Packaged HVAC Units

High-efficiency variable speed motors have been shown to save energy in supply air systems by operating motors at reduced speed when conditions allow. This study laboratory tested high-efficiency motor and drive systems applicable to supply air systems. A dynamometer was constructed and instrumented to conduct tests on 7.5 HP motors and variable frequency drives (VFDs). Five commercially available motors that used various drive technologies were chosen for the study. The technologies evaluated include traditional induction, synchronous permanent magnet, hybrid synchronous reluctance/permanent magnet, and switched reluctance. The motor, VFD, and combined system efficiency was measured from 9-100% of maximum torque and 30-100% of maximum speed. From the system efficiency results, curves of motor speed vs power were derived for a fixed-resistance duct system. The switched reluctance, permanent magnet and hybrid synchronous reluctance/permanent magnet motors and their drive pairs outperformed the induction motor and drive pairs in terms of efficiency. The switched reluctance motor was the most efficient motor at full-load while the hybrid synchronous reluctance/permanent magnet motor was the most efficient motor at the lowest load. Testing drive and motor pairs at multiple loads is important for characterizing the impact of product selection as the biggest relative differences are seen at the lowest loads. While there is great focus by the federal government on full-load motor efficiency, it is important to consider efficiency at part-load as applications of multi-speed systems increase.