Effect of the aquifer characteristics on heat transfer performance of deep borehole heat exchangers in water-rich geothermal reservoir via an improved multilayer calculation method

Limited research has been conducted on the relationship between the heat transfer performance of deep borehole heat exchanger (DBHE), widely employed in building heating, and the characteristics of the aquifer in which it is located. This study proposes an improved multilayer calculation model to fully analyze the heat transfer process of DBHE and simulates both internal and external conditions of the borehole. Field experiments are conducted on a demonstration project to validate the proposed model and algorithms. Simulation results demonstrate that as the Darcy velocity and aquifer thickness increase, energy efficiency coefficient of DBHE and the stratum temperature recovery also improve correspondingly. With aquifer thickness of 600 m and a Darcy velocity escalating from 0 m/s to 10 x 10(-7) m/s, average heat transfer capacity of DBHE ((-)Q) increased by 261.18 kW, representing a 26.34% rise in average energy efficiency coefficient of DBHE (E-). Similarly, at a Darcy velocity of 10 x 10(-7) m/s and an aquifer thickness ranging from 50 m to 600 m, (-)Q augmented by 216.85 kW, exhibiting a concurrent increase E- by 21.83%. Additionally, under a fixed aquifer thickness, with a decrease in multilayer aquifer configuration from 6 layers to 1 layer, E- exhibits an increase rate of 13.48%. The study provides guidance for the selection of DBHE system locations under complex geological conditions.