18 May 2017
This paper describes the theoretical and experimental study on high temperature heat pumps using a low GWP refrigerant. An HFO refrigerant R1234yf is selected to heat water or air to the temperature range from 65 °C to 80 °C while the temperature of source water or air is in the range from 7 °C to 25 °C. Sub-critical heat pump cycles with smaller degree of sub-cooling than 10 °C are discussed for low temperature-rise heating to reheat circulating hot water or circulating hot air, returning with temperature drop ranged lower than 10 °C. Further, sub-critical heat pump cycles with larger degree of sub-cooling than 40 °C were discussed and tested for high temperature-rise heating to supply hot water or air. An experimental apparatus and experimental results were presented. Regarding the sub-critical heat pump cycles with larger degree of sub-cooling than 40 °C, the experimental results have been obtained, which the heating COP reaches 4.0 when the hot water temperature is 80 °C and the source water temperature is 26 °C, and the heating COP reaches 4.0 when the hot water temperature is 65 °C and the source water temperature is 8 °C.