Efficiency Characteristics of Speed Modulated Drives at Predicted Torque Conditions for Air-to-Air Heat Pumps

摘要

Examples of system (motor + inverter drive) efficiencies of two types of adjustable speed control are compared for predicted compressor and indoor blower load profiles. The two classifications are inverter-driven induction motors (IDIMs) and permanent-magnet electronically commutated motors (PM-ECMs). Reference sine-wave-driven induction motor (SWDIM) efficiencies are also given. Available bench data on late 70's IDIM compressor drives are compared to recent data on IDIM and PM-ECM drives. The drive efficiencies are compared over common operating torque requirements for heating and cooling. A modulating heat pump model was used to develop predicted reciprocating compressor torque/drive-frequency mappings and the expected operating torque ranges. The variation in modulating compressor torque requirements is analyzed. Ways to adjust the torque relation for different compressor types and sizing strategies are also discussed. Modulating blower performance data on an early '80s generation modulating heat pump with an IDIM drive (and SWDIM reference drive) were obtained from Miller (1988) and compared to bench data on recent IDIM and PM-ECM drives under similar torque conditions. In both compressor and blower applications, the combined system efficiency of the PM-ECM drives is nearly equal to or higher than that of the reference SWDIM cases and significantly better than IDIMs available in the late '70s. When compared to more recent IDIMs, the PM-ECM efficiency advantage over IDIM compressors has been reduced 40 to 50% between half and nominal speed (3600 rpm) but still remains 14 to 9% higher, respectively. For blowers, the IDIM improvement has not been as great. PM-ECM-driven blowers appear competitive at present with IDIM blowers on combined efficiency, cost, and reliability. For the compressor PM-ECM drives, if progress continues, these drives will likely be a leading candidate for future modulating heat pumps. 24 refs., 13 figs., 5 tabs. (ERA citation 13:018430)