A novel two-stage compression air-source heat pump cycle combining space heating, cooling, and domestic hot water production

Abstract

To improve the efficiency of HVAC system, a novel air-source heat pump based on the two-stage compression cycle is proposed. The heat pump shows the multi-function of producing the domestic hot water year-round, space cooling water in summer, and space heating water in winter. The theoretical model is developed to analyze the performance of heat pump under various conditions. Four high GWP refrigerants, including R134a, R32, R407, R410A, and four low GWP refrigerants, including R1234ze(E), R600a, R152a, R290, are compared and analyzed under various conditions. Besides, the effects of environment and system operation parameters, such as domestic hot water demand ratio, evaporating and condensing temperatures, on system performance are investigated. The major results are concluded: A multi-functional air-source heat pump shows high annual efficiency by switching both the four-way valve and tee valve. The low GWP refrigerant R152a shows the best performance among the selected refrigerants, especially for summer conditions, and the COP is higher than the R1234ze(E), R134a, R600a, R32, R407C, R410a, and R290, R152a by 10.4 to 9.0 %, 8.3 to 7.9 %, 5.6 to 4.0 %, 9.1 to 13.0 %, 20.9 to 23.3 %, 29.8 to 36.5 %, and 11.0 % under the selected condition, respectively. Compared with summer conditions, R152a improves COP slightly under winter conditions, especially for R600a and R134a (less than 5 % under the selected conditions). Besides, under the summer conditions, the system performance increases first and then decreases with the increasing domestic hot water demand. The maximum COP reaches 6.7 while the summer domestic hot water load ratio (SLR) equals 0.5 and the environment air temperature equals 25 °C. The heat pump also shows a good performance under winter conditions. The minimum COP reaches 2.4 with the air temperature of −25 °C and the winter domestic hot water load ratio (WLR) of unity. The result of this study hopes to promote the further improvement of the air-source heat pump and HVAC system.