EXPERIMENT ON THE PERFORMANCE OF AN AUTO-CASCADE HEAT PUMP SYSTEM USING ZEOTROPE REFRIGERANT MIXTURES

摘要

The temperature difference between condensation and evaporation is about 40～50 °C normally in single-stage compression heat pump, which will be larger in zeotropic refrigerant mixture auto-cascade cycle. The heating temperature difference and the applicability of single-stage heat pump would be enlarged if the zeotropic refrigerant mixture auto-cascade cycle was applied to heat pump. In this paper, an auto-cascade air source heat pump water heater was built. Using the NIST REFPROP7.0, the temperature concentration diagram of a typical binary zeotropic refrigerant mixture was drawn. With a series of experiments, the whole circulation process of auto-cascade heat pump water heater and influencing factors of COP under higher water temperature were analyzed. The results show that the internal heat exchanger between evaporative condenser and evaporator should be cancelled for better heat transfer in auto-cascade heat pump. The mass flow of cold flow can be reduced as the opening degree of the electron expansion valve J1 reduces, so the degree of superheat of compressor suction can be reduced and the heating effect of heat pump increases. Lower COP of auto-cascade heat pump is a disadvantage, and the way to improve it should be sought in the future.