Enhancement of Sub-soil Thermal Conductivity for Geothermal Heat Pump Systems with Rainwater Collection

A shallow rainwater collection tank is proposed to improve the thermal efficiency and significantly enhance the economic viability of geothermal heat pumps (GTHP). This system aims to use convective heat transfer within underground tanks as well as instant replacement of stored heat in the event of rainfall. Through a sensitivity analysis using Computational Fluid Dynamics (CFD), the temperature distribution and rainwater stream within the tank were successfully visualised. These results highlighted some of the influential design parameters that will improve the efficiency of heat transfer in the underground structure. The experimental study described here proposes practical design strategies for enhancing sub-soil conditions in order to optimise heat transfer properties in the adjacent ground. The results demonstrated the effects of water content, dry density and compaction energy on the thermal conductivity of the soil. In addition, a comparative analysis was undertaken between two measuring methods of thermal conductivity; the heat flow meter (HFM) and the dual-probe heat-pulse (DPHP) method. Economically priced underground structures and construction procedures are suggested.