Experimental study on the effect of compressor frequency on the performance of transcritical CO2 heat pump system with regenerator

Abstract

To clarify main factors that affect the discharge pressure and compressor frequency on air-source transcritical CO2 heat pump water heater, an experimental research is designed in which the discharge pressure is controlled by varying the expansion valve opening and the plant is tested at three different compressor frequencies (25, 30 and 35 Hz). The results show that both the gas-cooler outlet status of CO2 and the water-inlet temperature have significant effects on Q and COP. Qmax (the maximum heating capacity) and COPopt (the optimal COP) exist in the system. With the compressor frequency increasing from 25 Hz to 35 Hz, Qmax shows a rise of 30.0% and COPopt is decreased by 25.1%. Compared to COPopt, the COP corresponding to Qmax drops in a mild way. Thus, the system should be operated in a suitable situation between COPopt and Qmax undertheprecondition tosatisfytheactual heating needs. This paper not only provides reference for designing and further study on transcritical CO2 cycle, but also an operational strategy of air-source transcritical CO2 heat pump.