Influence of Groundwater Heat Pump system operation on geological environment by Hydro-Thermal-Mechanical-Chemical numerical model

Groundwater Heat Pump (GWHP) systems have gained attention for space heating and cooling due to its efficiency and low installation costs. It is known that thermal transfixion and land subsidence are main geological environmental hazards in the application of GWHP. But few studies paid attention to groundwater quality. In this research, a three-dimensional Hydro-Thermal-Mechanical-Chemical numerical model was established based on Biot's consolidation theory, solute and heat transport in porous media theory. The numerical model could evaluate geological environment from four aspects: hydraulic head, temperature, groundwater quality, and land subsidence. The coupling effect of building load and extraction-injection groundwater is considered to study land subsidence. The model is applied to a GWHP in Nantong, China. The results show that increasing the temperature change and decreasing the circulation ratio of GWHP will alleviate thermal accumulation, thermal transfixion, and freshwater salinization of the confined aquifer III. But it will aggravate the occurrence of land subsidence. The geological environment involves four factors. The development of shallow geothermal energy should be considered comprehensively. Optimizing operation scheme by changing the groundwater seepage field would alleviate geological environment deterioration.

Automated summary

This study established a numerical model to evaluate the geological environment of groundwater heat pump systems from four aspects: hydraulic head, temperature, groundwater quality, and land subsidence. The results showed that adjusting temperature change and circulation ratio could improve groundwater quality but aggravate land subsidence. The development of shallow geothermal energy should be considered comprehensively, and optimizing the groundwater seepage field could alleviate the deterioration of the geological environment.