摘要：In layered subsurface, the soil around a vertical borehole heat exchanger (BHE) contains different geological layers. Non-uniformity and groundwater flow can affect the performance of BHE drastically. In this paper, through the field investigation of boreholes in Zhu Shan, Nanjing, China, a numerical model considering five strata is developed. Using thermal resistance and capacity models for inside borehole and a combination of a locally refined grid for discretizing and solving the soil mass governing equations, the numerical model is calculated and validated by field test data. The maximum temperature difference never exceeds 0.3 °C. The numerical model is also compared with the homogenous finite line source (FLS) model. Based on the numerical multilayered model, the axial temperature profile at different distances under different heating times are presented and explored. After 60 days heating at the distance of 0.2 m to heat injection borehole, the maximum temperature rise is 9.2 °C in unsaturated soil layer, but the temperature rise in aquifer layer and in fractured layer are only 7.6 °C and 6.7 °C, respectively. Furthermore, two modified numerical layered models, in which the groundwater flow in aquifer or fracture layer is negligible, are established to analyze how the different layered characteristics impact on performance of BHE. The results showed that ignoring the groundwater flow in aquifer layer made the outlet temperature 0.7 °C higher than that of the original numerical layered model.
关键词：borehole heat exchanger (BHE); temperature response; multilayered subsurface; groundwater flow
