Temperature stage matching and experimental investigation of high-temperature cascade heat pump with vapor injection

High-temperature cascade heat pump has remarkable development potential for industrial heat generation due to its superiority in energy-saving and environment friendly. But the growing demand for higher temperature difference heating challenges the traditional cascade heat pump. One of practical solutions is the combination of cascade system and vapor injection technique. However, the introduction of vapor injection increases the complexity of the system, and the interaction between branches and the distributions of branches are to be studied to give full play to the best performance of the vapor injected cascade system. This paper focuses on temperature stage matching between the heat exchange branches of a cascade air source heat pump with vapor injection to get optimal heating performance. The optimal configurations of intermediate temperature and vapor injection branch temperature are obtained based on the optimal method. A cascade heat pump prototype with refrigerant R245fa and R410A is developed and investigated experimentally to verify the optimization method. The cascade air source heat pump could realize 140 °C heat supply and the coefficient of performance is from 1.16 to 1.58 under the ambient temperature of from −10 °C to 20 °C.