Integrated computational and experimental evaluation of thermal optimization in energy pile groups in soft clay

Energy piles, combining building foundations with ground source heat pump (GSHP) systems, offer a sustainable thermal solution for urban buildings. However, thermal interactions between adjacent piles and the unique thermal behavior of soft clay present challenges for efficient design and operation. This study aims to develop a computationally efficient approach to evaluate and optimize the thermal performance of energy pile groups installed in soft clay, using a combination of finite element modeling and experimental validation. A three-dimensional heat transfer model was developed using COMSOL Multiphysics and calibrated with data from a full-scale test site comprising 12 energy piles. Simulations were conducted for various pile group configurations (1, 2, 4, 6, and 9 piles) and operational time cycles (8, 10, 12, and 24 hours per day). The results demonstrate that increasing the number of piles leads to a 2.18–15.43% increase in surrounding soil temperatures due to thermal interference. Simplified multiplier factors (1.6498–2.9119) were proposed to estimate temperature distributions for grouped configurations. Reduced operation durations significantly delayed temperature saturation (by 85–103 hours) and decreased peak soil temperatures by up to 29% over five years. This research provides a practical, design-oriented framework for energy pile systems in soft clay, enabling accurate thermal assessment with lower computational requirements. The proposed method enhances the feasibility and efficiency of energy piles in high-density urban areas.