The difference between vapor injection cycle with flash tank and intermediate heat exchanger for air source heat pump: An experimental and theoretical study

Abstract

As a widely used technique, vapor injection plays an important role in air source heat pumps (ASHPs) which operate across a wide range of ambient temperatures. The one of primary solutions has been reported to be vapor injection based on flash-tank (FT) and intermediate heat exchanger (IHX) loops respectively. In this paper, vapor injection and its two typical configurations are experimentally investigated in an ASHP prototype. The results show that in the vapor-injection based ASHPs, the performance of FT based ASHPs is better than that of IHX based ones, and injected vapor improves mass flow rate and distribution of working fluid, with a hidden decreasing effect of exhaust entropy. In order to explore theoretical reasons, a whole system model is presented that quantifies performance enhancement potential of FT based and IHX based ASHPs respectively. The calculation results show increased refrigerant mass flow rate, its optimum distribution, and moderate injected vapor entropy contribute to performance improvement of vapor-injection based ASHPs. Further, we also visualize synergy between refrigerant mass flow and injected entropy from perspective of negentropy. At the negentropy level, FT based rather than IHX based loop brings higher heating capacity and efficiency, which is consistent with measurements from experimental research.