Effects of aquifer on heat exchange process in geothermal applications

Abstract

Geothermal energy has been widely used in the field of the building heating through the ground heat exchanger (GHE). The groundwater flow in the aquifer is one of the significant factors affecting the heat exchange process between the GHE and ground by promoting the pure conduction to the conjugated convection and conduction heat transfer. In this paper, the variations of the ground temperature field and the thermal influence radii subject to the existence of aquifers were investigated numerically. The geometrical models consisting of a coaxial heat exchanger, multiple aquifer and aquifuge layers were established to study the effect of groundwater velocities and the number of aquifer layers on the GHE system. The results reveal that the heat exchange capacity of the GHE is enhanced when the groundwater velocity increases. The increased number of aquifer layers can also enhance the heat exchange capacity with the tested groundwater velocity at 315 m/a or 31.5 m/a, but would weaken it with the velocity of 3.15 m/a. In addition, it is found that the aquifuge temperature field is affected by the aquifer layer, and the thermal influence radius of GHE is dominated by the groudwater velocity of aquifers when the velocity is larger than the critical velocity. Conversely, the thermal influence radius is governed by the thermal diffusivities of aquifuges for the groundwater velocity samller than the critical velocity.