| The heating performance of the conventional air source heat pump with single-stage compression(SSC) cycle severely decreases under low ambient temperature condition. It can effectively improve the heating capacity of the heat pump system and reduce the discharge temperature of the compressor to use the economized vapor injection(EVI) technique. In addition, the use of environmentally friendly refrigerant R32 in the air source heat pump(ASHP) unit can reduce the amount of the refrigerant charge and increase the economic benefits. Therefore, the heating performance of the EVI ASHP system using R32 in this study is of important theoretical significance and practical value.Firstly, on the basis of theoretical analysis about the compression process with injection in a gas-injected scroll compressor, the computer program to simulate the performance of the EVI heat pump system was developed by EES software in this paper. The heating performance of the EVI heat pump system and SSC heat pump system under different conditions were simulated, and the effect of the injection-hole location on the heating performance of the EVI heat pump system was analyzed. Secondly, the EVI heat pump prototype was tested in the psychrometric rooms. The heating performance of heat pump as SSC system model and EVI system model under different working condition was measured. The effects of the injection pressure on the injection ratio, heating capacity, power consumption, heating COP and discharge temperature of compressor of the EVI system were analyzed, and the heating performance of the EVI system and SSC system was compared. Finally, the simulated data were compared with the experimental results. The conclusions are as follows:(1) The experimental results indicate that the injection ratio, heating capacity and power consumption of the EVI system increase as a result of the increase of the injection pressure, and the discharge temperature reduces with the increase in the injection pressure. As the ambient temperature is below-5℃, the heating COP increases and then decreases with the increase of the injection pressure. So there is an optimum injection pressure, at which the heating COP of the EVI system reaches the maximum value. For the EVI heat pump system, the optimum injection pressure is observed between 1.67 MPa to 1.78 MPa.(2) The simulated and experimental results show that under optimum injection conditions the heating capacity and the power consumption of the EVI system are higher than these of the SSC system respectively, and the discharge temperature is lower than that of the SSC system. As the ambient temperature is below-3℃, the heating COP is higher than that of the SSC system. As the ambient temperature is above-3℃, the heating COP is lower than that of the SSC system. Therefore, the optimum switch-point between the EVI system and the SSC system is about-3℃.(3) The simulated and experimental results indicate that the heating capacity, power consumption and heating COP of the two systems decrease with the decrease in the ambient temperature, and the discharge temperature increases as a result of the decrease of the ambient temperature. The decreasing rate of the heating capacity and heating COP with the ambient temperature of the EVI system is lower than that of the SSC system. The discharge temperature of the scroll compressor with vapor injection is below 105℃ at the ambient temperature of-10℃, and when the ambient temperature is above-10℃ the EVI ASHP unit using R32 can operate safely and reliably.(4) The simulated results indicate that as the volumetric ratio of the scroll compressor increases from 1.1 to 1.6, the injection pressure and the discharge temperature of the compressor increases by 31% and 9% respectively, and the injection ratio, heating capacity and power consumption decreases by 33%, 4% and 7% respectively, at the ambient temperature of-10℃. Therefore, the EVI system has the high heating capacity and the low discharge temperature of the compressor at the volumetric ratio of 1.1. |
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