Theoretical and experimental investigation on the rolling piston compressor with enhance vapor injection for heat pump system

The rolling piston compressor with enhanced vapor injection (EVI) is widely used in the household air-source heat pump system. To study the thermodynamic performance and the optimal injection pressure, this paper presents a mathematical method to simulate the whole working process of rolling piston compressor with EVI, which considers suction backflow process, discharge process, vapor injection process and leakage process. Ac-cording to the calculation, the effects of injection pressure on discharge mass flow rate, p-V diagram and indi-cated power have been analyzed. In order to verify the accuracy of simulation, an experiment has been carried out to obtain the discharge mass flow rate and the errors between simulated and experimental results are within 4%, which shows that the proposed method is precise enough. Additionally, the experimental results show that EVI can not only improve the heating capacity and COP but also decrease the discharge temperature. However, the optimal injection pressure corresponding to the maximum heating capacity is different from that corre-sponding to the maximum COP. From the perspective of the heating capacity, the optimal injection pressure is a little higher than the geometric mean of suction pressure and discharge pressure but from the perspective of COP, the optimal injection pressure is a little lower than the geometric mean.