Impact of Boundary Conditions on a Groundwater Heat Pump System Design in a Shallow and Thin Aquifer near the River

摘要

The exploitation of shallow geothermal energy through a groundwater heat pump (GWHP) is always limited to thick and deep aquifers containing abundant water with a relatively stable temperature. Unfortunately, aquifers in hilly regions which occupy two thirds of China are usually thin and shallow. The boundary conditions in those hilly areas affect the groundwater flow that is used for geothermal energy production. To quantify the impact of boundary conditions on the shallow geothermal energy development, a shallow and thin aquifer near the Qingyi River in Anhui Province was chosen as a case study, and a three-dimensional heat–water model was developed using FEFLOW. The impact of the boundary conditions on the hydrodynamic and temperature fields of the aquifer was analyzed by using the developed model. Furthermore, the well locations of a pumping-recharging system near the river correspond to three different modes of pumping-recharging well layouts that were optimized based on the changes of pumping water temperature and the maximum drawdown. The simulation results indicated that the influence of atmospheric temperature on groundwater temperature is negligible below a depth of 11 m. When the river level is above 28 m, the optimal scheme of pumping-only was used (without considering recharging wells) with a certain distance from the river. This scheme not only operates efficiently, but also reduces the operation cost.