Simulation research of a hybrid heat source heat pump using R134a, R744 instead of R22 for domestic water heating in residential buildings

The heat pump water heater with hybrid heat source is a promising device using in residential buildings, which selects collector/evaporator gathering solar and air energy as the heater in order to reduce energy consumption. The performances of self-designed heat pump with hybrid heat source using different refrigerants were simulated in the present work. Based on the lumped parameter method, the steady state models, including collector/evaporator, compressor and gas cooler, were established. The effects of R22, R134a and R744 were analyzed in terms of power consumption, heat capacity, coefficient of performance (COP) and so on. The results showed that the heating capacity as same as the power consumption for the three refrigerants performed a same linear change tendency. However, within the ambient temperatures range of 5-13 °C, the COP of R744 was higher than the ones of R134a and R22. When ambient temperature was higher than 13 °C, COP of R134a was highest. With respect to the heating time, the heating time of R22 was the shortest when equal amount of water was heated from 15 °C to 55 °C at all corresponding outdoor temperatures. Besides, the solar energy input ratios of R22, R134a and R744 were changed in the range of 30-44%, 48-89% and 39-73%, respectively, at all corresponding outdoor temperatures.