A novel auto-cascade heat pump system with intermediate throttling was proposed. The inlet condition of the separator is not influenced by the outlet condition of the condenser by adjusting the intermediate pressure. The performance of the novel auto-cascade heat pump system was compared with that of a conventional auto-cascade heat pump system via our computing program. The results show that when the condenser outlet quality is from 0.2 to 0.4

the system performance can be optimized and the suction with the liquid refrigerant in a conventional auto-cascade heat pump system can be avoided in the novel auto-cascade heat pump system. The heating coefficient(C

COP

)and the volume heating capacity of the system proposed are 19.1% and 28.9% higher than those of an optimized conventional auto-cascade heat pump system

respectively.