Study on Feasibility of Accumulating Solar Energy into Soil for Improving the Imbalance of Heat Injection and Extraction in GHP System

Geothermal heat pump system (GHP) is efficient to utilize renewable energy in cooling and heating of building. However, the major problem is that the coefficient of performance (COP) of GHPs will decay after a long-time operation because of the imbalanced energy injection into and extraction from the ground. It is an effective way to apply solar collectors in the GHPs to collect thermal energy in the non-heating season and deliver the heat into ground, which may relief the imbalance. In our research, a demo project of solar-assisted geothermal heat pump system (SAGHP) in a rural building in Xi’an was built up, which delivers hot water from solar collector into soil from September 1 to November 14, 2018. For analyzing the effectiveness of elevating the ground temperature, a TRNSYS model was established, verified by the measured data in the project, and served for simulating three systems, which including the SAGHPs without accumulating solar energy in soil, the SAGHPs with accumulating thermal energy in soil in summer, and the SAGHPs with accumulating thermal energy in soil in autumn. The comparison of systems showed the significance of thermal storage in Xi’an and the feasibility of thermal injection in autumn for solar collection for improving the heat imbalance of GHPs.