Study on the performance assessment of a novel hybrid heat pump system modified with dedicated mechanical sub-cooler for domestic heating applications

This article investigates the performance of a novel hybrid heat pump system, which is developed to recover the waste heat from the flue gas of domestic heating boiler. The purpose of proposed system is: to increase the return water temperature, to heat the boiler supply air, and to provide the hot air for indoor heating. The developed system consists of an air heater (acts as a dedicated mechanical sub-cooler), a multistage condensing economizer and a vapor compression heat pump. A test case of common building is considered for the performance assessment of system, which is based on the 4E analysis. For this purpose, ten refrigerants are selected. The results show that about 25.58% increase in the coefficient of performance can be obtained for the proposed model as compared to simple vapor compression cycle if operated with R245fa, which also have a lowest exergy destruction rate (38.27%) as compared to other studied refrigerants. From the perspective of improvement in boiler’s energy and exergy efficiency, R114 is used to be the most effective among other refrigerant (10.33% increase in energy efficiency and 4.74% increase in exergy efficiency). Parametric study results have shown that the variation in ambient conditions should be considered carefully while selecting a refrigerant to significantly improve the system performance, exergy efficiency, and relevant economics on regional basis. From the obtained results, a novel yet simple refrigerant selection approach is proposed which can also be adopted for other thermodynamic cycles.