Design, optimization and energy performance of hybrid Photovoltaic-Thermal solar-assisted heat pump systems for buildings applications in Algeria

Abstract

The demand for solar-assisted heat pumps is increasing over time to meet human needs for home comfort, such as heating and domestic hot water, while maintaining lower costs. This trend aligns with the commitment of governments around the world, including Algeria, to provide clean renewable energy and move away from polluting fossil fuels that contribute to gas emissions. The energy source for operating a heat pump system can be single, such as solar energy alone or air energy alone or can be dual or multiple sources in same time, meaning the heat pump system operates using more than one source of energy, like solar energy and air. Solar heat pump systems are divided into two types. One is referred as the direct-expansion system, abbreviated as DX-SAHP, where the solar collector acts as the evaporator at the same time and the other type is referred as the indirect-expansion system, abbreviated as IX-SAHP, where the solar collector and the evaporator are separated from each other. The contribution of this study is to design and optimize a new dual solar-air heat pump system that can operate in directexpansion mode (DSM), or in indirect-expansion mode (ISM) and it can also operate in a third mode Direct/indirect-expansion (D/ISM). The objective is to investigate and compare the performance of the new system when operating in the three modes. First, a mathematical model for DX-SAHP system based on the fundamentals of thermodynamics and heat transfer is developed, validated and implemented in MATLAB. Then, a TRNSYS model simulating IX-DSHP system type is developed. In the third step, the two models are integrated to obtain the new DX/IX-DSHP system. Results show that when the system operates in D/ISM mode, it achieves better performances. The coefficient of performance is 2.89, the seasonal performance factor is 9.19 and the solar fraction is 63%. Whereas, they are 2.63, 6.23 and 51% in ISM and are 2.41, 3.76 and 29% in DSM. Parametric study indicates that the area of the solar collector, whether conventional thermal collector or photovoltaic thermal collector, has a direct effect on performance, while the set-point temperature of the tanks has a minimal impact. Economically, the D/ISM shows a shorter payback period compared to the other two modes if global energy prices are considered. The PBP is 7, whereas it is 8 and 9 in the ISM and DSM respectively