Heating experiments of a solar-assisted heat pump and thermal equilibrium simulations of geothermal fields

This study aims to explore technologies required for clean energy heating by means of multi-energy complementation, with the purpose of meeting the demand for clean heating in decentralized buildings in Beijing's villages and towns. To this end, this study built a solar-ground source heat pump (SGHP) compound system in a rural area of Beijing. Then, it carried out heating experiments of the solar-assisted heat pump system and thermal equilibrium simulations of geothermal fields using the COMSOL software. The results are as follows: (1) Compared to a single SGHP system, the solar-assisted heat pump scheme increased the outlet water temperature on the ground source side by 23% and increased the coefficients of performance (COP) of the heat pump system and units by 19% and 25%, respectively. (2) After ten years of operation of the system, the scheme of a single season operation using a single SGHP system exhibited a total extracted heat higher than the natural recovery in the intermittent period, with a total balance in the geothermal field of −8.91×10⁹ kJ. (3) The schemes of two-season operation using a single SGHP and a solar-assisted heat pump individually yielded total extracted heat less than that the total discharged heat, with total balances in geothermal fields of 4.220×10⁹ kJ and 1.084×10¹⁰ kJ, respectively. Therefore, the dual-season schemes will not produce a negative heat balance to the geothermal field but a certain heat supplement instead. Supplementing solar energy to the SGHP system during its operation exerts a smaller impact on the geothermal field and can significantly improve the efficiency of the heating pump system and units. This mode is suitable for rural areas in Beijing, especially for buildings with high heating demand.