Experimental Research on Performance of Cascade Heat Pump with Variable Rotation Speed of High-temperature Compressor

To study the effect of a variable rotation speed compressor on the performance of a cascade heat pump, an experimental platform was constructed. The changes of discharge temperature, intermediate temperature, heating capacity, power consumption, and Coefficient of Performance (COP) with different rotation speeds of a high-temperature compressor were studied experimentally. Experimental results demonstrated that the system operated safely and reliably under the condition of a condensing temperature of 46 °C and an evaporating temperature between -35 and -10 °C. As the high-temperature compressor speed varied from 1200 to 6000 r/min and the condensing temperature was 46 °C and the evaporating temperature -25 °C, the heating capacity increased by 129.7%, and the low-temperature compressor power decreased by 43.4%. In addition, the COP initially increased and then decreased with the increase of high-temperature compressor speed; there was a maximum COP and corresponding optimal high-temperature compressor speed.