Shibin Geng

Evaluation of Thermal Anomalies in Multi-Boreholes Field Considering the Effects of Groundwater Flow

In this paper, the performance of multiple boreholes (multi-BHEs) field is evaluated by considering the groundwater flow. Optimization strategies are presented to mitigate thermal anomalies in the BHEs field. This study shows that groundwater flow greatly improves the heat transfer but causes thermal anomalies downstream. To overcome this problem, a heat transfer model is established for multi-boreholes based on temperature field superposition and moving finite line source model (MFLS). The MFLS multi-boreholes model considers the axial effect and groundwater flow and produces results in agreement with the field tested data of a 4 × 4 boreholes field. Using a dynamic annual load pattern, the long-term performance of the 4 × 4 boreholes field is analyzed. Three dynamic diurnal cooling load models are proposed to evaluate the temperature changes in the underground. The intermittent load model could reduce the local temperature anomalies in downstream tubes. The optimization model for cooling cases for multi-BHEs is elaborated to keep the outlet temperature as low as possible and minimize the extreme temperature anomalies, and by this, ultimately improve the system performance. Furthermore, the temperature variations and thermal anomalies downstream of multi-BHEs are investigated by evaluating the arrangement optimization and load optimization. The results show that the optimization could mitigate thermal anomalies downstream and reduce the rate of temperature imbalance of the BHEs field.