Increasing the air source heat pump efficiency at low ambient temperature by using a two-phase ejector

Abstract

The use of an ejector as expansion device is one of the alternative ways to improve the performances of an air source heat pump at low ambient temperature. This article presents a theoretical energetic and exergetic analysis of an ejector expansion vapor compression heat pump with on/off control. By using the ejector, the expansion throttling process is replaced by an adiabatic expansion. Furthermore, compressor operation is much improved due to lower compression ratio and reduces the temperature of the working medium at the end of the compression process. It also enables to reduce size of the evaporator, It also enables to reduce size of the evaporator, by using a phase separator. The results show that, by using an ejector instead a throttle vane in basic vapour compression cycle, both the energy efficiency and the exergetic efficiency of the cycle increase. The phase separator placed after the ejector has a significant influence on the cycle performance too. The exergy loss in every heat pump components is calculated. Thus, it can be seen that the process needs to be improved for better performance of the heat pump. The results highlights that the most important exergy loss at low ambient temperature have place in the compressor.