Analysis of performance and economical efficiency of two-stage compression heat pump system with inter-stage injection in cold regions of northern China

The low temperature adaptability of air source heat pump in the field of building heating in cold regions has always been a hot topic. At present, the combination of inter-stage injection technology and two-stage compression can effectively solve the problem of low temperature adaptability. Therefore, in the present paper, the two-stage compression heat pump system with inter-stage injection was taken as the research project. Based on the simulation model of the two-stage compression heat pump system, the process of inter-stage injection coupling between the low-stage compressor and the high-stage compressor was analyzed. Based on the experimental results, the effects of inter-stage injection process on the inter-stage pressure, inter-stage temperature and thermal performance parameters of the two-stage compression system were analyzed. The results show that as the mass of inter-stage injection increases, the inter-stage pressure will increase significantly and then increase slowly; and the inter-stage temperature will increase slowly and then decrease significantly; both the heat output and the COP will increase first and then slightly decrease. In addition, the heat output will increase by about 8%–15%, and the COP will increase by about 5%–12%. Finally, the two regions including Beijing and Dalian in China were selected, and the economical efficiency of the system in applications was analyzed in combination with the experimental results of variable working conditions of the system.