conventional refrigerant heat pump system, two rolling piston expander, simulation analysis, friction loss
An expander is employed to replace a throttling valve in a heat pump system of the conventionorder to further improve the efficiency of the system by recovering partial expansion work to decconsume of the system. Due to large expansion ratios of conventional refrigerants, a twone-stage expander was proposed and designed. Simulation analysis was developed by analyzing irreversible losses in the expansion work process. The simulation results show that, friction losses of a conventional refrigerant expander are 80.2% of total losses, which are the main factors to influence the efficiency of expander. Then the measures of reduciong friction losses are presented, which would be expected to improve the expander efficiency efficiently.