Performance evaluation of a geothermal energy wall considering effects of groundwater flow with thermal–hydraulic characteristics of soil

• Neglecting groundwater flow leads to underestimation of EWS thermal performance. • The effect zone differed significantly between the left and right sides of the EWS. • Natural, mixed, and forced convection regimes identified for different flow rates. • Convection enhances EWS heat exchange by 41.5% to 73.1% compared to conduction. • Outlet fluid temperature reduced by 8 °C to 15 °C owing to convection effects. Thermally induced groundwater (GW) flow can significantly influence heat-transfer performance and soil temperature during the operation of an energy wall system (EWS). However, few studies have quantitatively evaluated the influence of thermal convection on EWS performance, particularly with respect to outlet fluid temperature (°C) and heat exchange rate (W). This study investigated the influence of three convection regimes—natural, forced, and mixed—induced by GW flow on the heat-transfer performance of an EWS. A finite element method-based 3D numerical model was employed to simulate the actual dimensions of a subway station constructed in Gwangju, South Korea. The model was validated using an in-situ thermal response test with a steel U-type heat exchanger embedded in a concrete volume of 2 × 3 × 5 m (width × depth × length). The results indicated that natural convection was dominant at GW velocities below 10 −7 m/s, whereas forced convection was dominant at GW velocities above 5 × 10 −6 m/s. Mixed convection (a combination of forced and natural convection) was observed between these ranges. For the summer season (cooling model, where lower outlet fluid temperature indicates improved performance), the thermally induced GW flow resulted in a reduction of the outlet fluid temperature of approximately 8 °C, 11 °C, and 15 °C for natural convection, mixed convection, and forced convection, respectively, compared to that of only conduction heat. Consequently, the heat exchange of the EWS was enhanced by 41.5 %, 56.8 %, and 73.1 %, respectively. These findings suggest that neglecting thermally induced GW flow can lead to a significant underestimation of EWS performance and provide valuable insights for the accurate estimation and design of such systems.