OT-88-06-2 -- Measured Efficiency of Variable-Speed Drives in Heat Pumps PDF

Two variable-speed heat pumps were tested under controlled speed and temperature conditions to characterize system performance and compressor, motor, and inverter losses. Heat pumps were selected from the top of the domestic product line from two Japanese manufacturers. Both employed rolling-piston compressors. One was driven by a brushless DC motor; the other, a three-phase AC induction motor. Each inverter control circuit was analyzed to determine a means for controlling the compressor speed independently without altering the inverter output waveform. Heating and cooling capacity and COP were determined for each heat pump for a range of speeds and outdoor temperatures, using refrigerant-side measurements. Each compressor was disassembled, and the motors were tested separately on a dynamometer to measure motor and inverter efficiencies. Efficiency and thermodynamic performance results are presented, along with observations and recommendations for further testing.

Units: Dual