Oil flooded compression cycle enhancement for two-stage heat pump in cold climate region: System design and theoretical analysis

•COP of proposed system improves up to 17.2% compared with vapor injection cycle.•Discharge temperature of proposed system is largely decreased.•Proposed system is beneficial for refrigerant with high compression heat.•Proposed system has potential for applications in cold climate heat pump. In order to improve the performance of air source heat pump in cold climate region, a combined oil flooded compression with regenerator and vapor injection cycle system is suggested in this paper, which integrates oil flooded compression with regenerator into a conventional vapor injection cycle. A mathematical model is developed and parametric studies on this cycle are conducted to evaluate the benefits of the novel system. The performances of the novel system using R410A and R32 are compared with those of vapor injection cycle system. The improvement of coefficient of performance (COP) can reach up to nearly 9% based on the same isentropic efficiency, while 17.2% based on assumption that there is a 10% rise in isentropic efficiency brought by oil flooded compression cycle. The heating capacity is reduced by 8–18% based on the same volumetric efficiency, while could be less than 10% in a practical system. The discharge temperature is largely decreased and can be below 100°C at −40°C Te and 50°C Tc condition for R32. The theoretical results demonstrate this novel heat pump has a high potential for improving the performance of air source heat pump in cold climate region.