Thermodynamic Analysis of a Cascade Heat Pump Incorporated in High-Temperature Heating System

In this article is presented thermodynamic analysis of a cascade heat pump system designed for using in high-temperature heating systems The own thermodynamic model was built by using properties of working fluids from the Coo/Prop base. The cascade heat pump was designed to use ambient air as heat source with temperature t(amb )= -20 degrees C and for heating water in the high-temperature heating system up to 70 degrees C. The projected heating capacity of the cascade heat pump was 100 kW. The coefficient of performance (COP) of the cascade heat pump system due to use of different working mediums combinations in cycles of the cascade heat pump was investigated. For the best combination of working fluids (mediums) sub-cooling super-heating pressure loss in compressor's suction line, as well as exergy efficiency of the heat pump were analysed as a function of the temperature of the cascade heat exchanger.