Heating and cooling geothermal systems in urban settings: The potential of energy micropiles

Since the 1980s, the utilization of geostructures for heating and cooling buildings has evolved significantly, initially with base slabs and later expanding to include various structures like piles, retaining walls, and tunnels, collectively termed as energy geostructures. These systems facilitate heat exchange between the ground and buildings by circulating a heat exchange fluid through plastic pipes embedded within the geostructures. In the realm of structural rehabilitation and retrofitting, micropiles have gained preference over traditional piles due to their smaller installation equipment, reduced noise, and limited vibration, making them an attractive option, particularly in densely populated urban areas. However, despite the potential of energy micropiles (EMPs), they have received little attention compared to energy piles. This study conducts a comprehensive review on geothermal energy and EMPs, highlighting their potential in heating and cooling structures in urban areas. Their long-term heat exchange rates, typically ranging from 30 to 50 W/m, are influenced by factors such as pipe configuration, pipe diameter, fluid flow rate, soil thermal conductivity, groundwater presence, temperature differentials, and seasonal variations. The small dimensions of micropiles may lead to increased thermal resistance due to interference between U- shape pipes, while group installations can reduce individual micropile thermal efficiency. Moreover, significant thermal stresses are induced, and they increase with cycles. Optimal performance is achievable with corrugated pipes, a coaxial pipe configuration and intermittent operation. This study highlights the need for continued innovation and partnership to advance the adoption of EMPs, thereby enhancing energy efficiency, climate resilience, and environmental sustainability. • Big cities face spatial constraints for geothermal installations. • Foundation retrofitting of existing buildings often involves using micropiles. • Energy micropiles (EMPs) offer structural reinforcement and energy retrofitting potential. • The compact dimensions of micropiles present thermal design challenges. • Coupled thermo-mechanical behavior of energy micropiles.