NUMERICAL ANALYSIS OF A SOLAR-ASSISTED DUAL-SOURCE HEAT PUMP COUPLED WITH A THERMAL STORAGE FOR RESIDENTIAL HEATING

According to the COP26 conference, the main goal of the European Union is to limit both the pollutant emissions to become climate neutral in 2050 and the global warming, by setting to +1.5 °C the upper threshold for the ambient temperature increase. In this regard, sectors of heating and cooling in buildings must be decarbonized. This aspect can be faced by limiting the direct and indirect global warming contributions, through the use of environmentally friendly refrigerants, high-performance components and the employment of renewable sources. In this context, solar-assisted heat pumps (SAHPs) can be considered as interesting alternatives to conventional systems, in order to reach all the European targets in terms of reduction of the yearly energy consumption. This work proposes a numerical model of an indirect expansion solar assisted ground multi-sources (air, sun, ground) heat pump for residential heating. To cope with the mismatch between the solar availability and the thermal energy demand and to take full advantage of the solar radiation, a storage tank on the source side has been considered. A control strategy between different operating modes has been established in order to maximize the system coefficient of performance (COP), and dynamic simulations in Naples climate conditions have been performed. An optimization of several design parameters of the machine such as solar collector surface, storage tank volume and heat transfer surfaces of heat exchangers has been carried out, to maximize the seasonal performance (SCOP) of the system and minimise the investment costs. Although the adoption of a solar side and a geothermal heat exchanger (GHE) led to higher SCOP values, results show that more convenient solutions in term of total costs are the ones of a traditional heat pump for short lifetime periods, and the ones with solar loop and heat pump working in parallel for higher lifetime periods.