The Green’s function based analysis for seasonal heat storage and utilization in a solar-geothermal building

A bi-directional geothermal heat exchange system is designed for building-integrated photovoltaic thermal (BIPVT) systems, which transfer heat between the building roof and a spherical geothermal tank. The heat transfer between the building envelope and tank is simulated with annual harmonic temperature variations. The thermal fields around the geothermal tank depend on the depth and size of the spherical tank, the heat exchange rate, the thermal damping distance, and the ambient temperature pattern of the area. Using Green’s function and Eshelby’s equivalent inclusion method (EIM), we simulate the thermal interaction between the heat source from the water tank and the surrounding earth through equivalent homogenization, and the material mismatch in thermal properties is simulated by continuous eigen-field distributions. Numerical case studies demonstrate the effect of the effective thermal properties and geometry of the heat source. The thermal damping distance and the distance between tanks play a crucial role in the influence zone of the tank: with burial depth over 3 times the damping distance, the effect of ambient ground temperature variation on stored-energy change is < 5 % ; with center-to-center distances over 4 times the radius, the multi-tank interaction effect on stored-energy change is < 5 % . • Homogenize spherical tank to a medium with equivalent thermal resistance and heat capacity. • EIM validated against multi-region BEM; computation cost reduced over 100 times. • Demonstrate key factors on damping distance, heat source, and size of tanks. • Design rules: bury depth over 3 times damping distance; spacing over 4 times tank radius. • Open-access EIM code for solar-geothermal layouts with customizable thermal properties.