Effects of aquifers on soil temperature distribution around deep buried heat exchanger

Deep buried heat exchanger has been increasingly applied into the building heat source through the utilization of geothermal energy. During the geothermal system design process, the aquifer is an important factor that affects the overall performance prediction. The flow of underground water at different positions changes the temperature distribution of the soils around the buried pipe and then influences the heat exchange at different depths. Consequently, the variation of the temperature field causes the thermal radius of the heat exchanger no longer regularly distributed, which affects the determination of the well spacing. With the aims of improving the accuracy of performance estimation, the aquifer effect is carried out by this study. The solution to the moving line source theory is used to acquire the temperature response at different positions. The overall effect of the underground water with different velocities on the performance is evaluated. The soil temperature distribution in the heat exchange zone with aquifers at different depths is studied in detail. The predicted thermal influence radius at different depths with various groundwater velocities and soil thermal properties showed that the temperature distribution around the buried heat exchanger is largely influenced by the groundwater movement. Under the simulation condition, the thermal radius increases from less than 10 m for pure conduction condition to a maximum value of 25.3 m with groundwater flow. The aquifer enhances the heat absorption of the heat exchanger, but the high flow rate also leads to a large thermal radius. The obtained thermal influence radius under different conditions can provide guidance for the design of the geothermal system.