Investigating the impact of temperature recovery across different thermal activation scenarios of a real-world energy piled foundation

Abstract

Energy piles (EPs) exploiting low-enthalpy geothermal energy for the seasonal air conditioning of buildings are mature examples of Energy Geostructures (EGs), with several case studies all over the world showing satisfying performance for years. Over time, comprehensive research has explored and proven the potential of this technology, with a particular emphasis on assessing the performance of EP groups. This work presents a real case study of an energy-piled foundation, where all the piles have been equipped with pipes to potentially operate as heat exchangers with the ground. Based on the available data on the building design and the results of thermal property tests performed on soil samples collected on-site, a long-term thermo-mechanical analysis was carried out on a three-dimensional (3D) model of the soil-foundation system. Unlike previous studies, this work specifically examines the effects of selective pile activation and alternate-year thermal recovery on their long-term performance. The main objectives of this study are: i) to quantitatively assess the impact of seasonal variations in energy demand on soil temperature in shallow geothermal processes, given that maintaining a consistent ground temperature throughout the year is crucial for efficient heat exchange operations and long-term stability, and ii) to investigate how selectively activating specific parts of the foundation may provide advantages or disadvantages in terms of both mechanical performance and energy efficiency. By dividing the foundation piles into subgroups, three configurations of piles' thermal activation were analyzed to assess the influence of the alternate-year of temperature recovery on the system’s global performance. The research aims to optimize soil thermal recovery, mitigate thermal imbalances, and enhance the sustainability and operational effectiveness of shallow geothermal systems, offering insights crucial for the design of more efficient and resilient EGs. The results indicate that alternating-year configurations do not lead to improved soil thermal recovery, as evidenced by the thermal flux values at the pile-soil interface, while the spacing between active piles significantly influences the mechanical response by reducing stresses and thermal-induced displacements during inactive periods.