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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 CoolProp base. The cascade heat pump was designed to use ambient air as heat source with temperature tamb= -20 °C and for heating water in the high-temperature heating system up to 70 °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 mean temperature of the cascade heat exchanger. [ABSTRACT FROM AUTHOR]

Abstract: Retrofitting of fossil fuel powered hot water radiator heating systems of the existing buildings by groundwater heat pumps can provide significant energy savings followed by economic and environmental benefits. The paper describes the procedure for selection of optimal low-temperature groundwater heat pump vapor compression cycle based on thermodynamic analysis of applied high temperature heat pump heating system. In comparative energy and exergy analysis observed are six different heating cycles, five of which utilize two-stage refrigerant compression, and one operate as basic one-stage heat pump system with an auxiliary heater. The systems validation is performed accounting strongly for the boundary conditions of the selected location. [Copyright &y& Elsevier]