Thermodynamic Optimization Of Cascade Heat Pump

Abstract

In today’s modern world, development of industry and technology has led to the increase in energy demand. Hence, more fossil fuels are burnt in order to cover this demand. Due to the multiple disadvantages, as well as the neg-ative impact that burning of fossil fuels has on the environment, heat pumps are gaining more importance when provid-ing energy for heating. This paper is aimed at conducting thermodynamic optimization of cascade heat pump in terms of different working fluid combinations and calculating maximum COP. In order to perform thermodynamic analysis, a software program that uses database of working fluids, was developed. The intermediate temperature within cascade heat exchanger represents a crucial parameter when analyzing and designing cascade heat pumps. Thus, when per-forming thermodynamic analysis, the intermediate temperature was varied in the range from 0⁰С to 25⁰С and the opti-mal temperature that provides maximum COP was defined. The analysis was performed on an air-to-water heat pump, that could be used for heating different types of buildings in places in Serbia where the outdoor design temperature is -20⁰С. The cascade heat pump would be used alongside radiator heating system operating at temperatures 70⁰С/50⁰С. Due to the high temperature difference between heat source and heat sink, cascade heat pumps have advantages over single stage or multi stage heat pumps. The optimization was performed on an air-to-water cascade heat pump where the evaporation and condensation temperatures were -25⁰С and 75⁰С, respectively. Following the conducted optimization, the analysis of the impact that isentropic efficiency of compressor has on COP was examined.