Energy Geostructures: Analysis from Research and Systems Installed around the World-Paper

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Energy geostructures use foundations and underground structures—such as piles, retaining walls and tunnels—as both load-bearing elements and ground heat exchangers. Pipes embedded in concrete circulate fluid connected to heat pumps, providing renewable heating and cooling. Because these structures are built for structural purposes anyway, integrating geothermal loops can reduce installation costs and construction time compared with separate borehole systems.<br /><br />The authors compiled a global database of 151 operational and trial installations: 119 energy piles, 20 energy walls and 12 energy tunnels. Installations increased substantially from 2005 to 2011, particularly in the UK, Austria and Germany, although the database is incomplete and reflects limited information from some regions. Piles remain the most common application; walls and tunnels are emerging technologies.<br /><br />Reported heat exchange is generally 40–120 W per metre of pile and 10–50 W per square metre of wall or tunnel. Performance depends on ground thermal and hydraulic conditions, groundwater flow, structure geometry and system design. Tunnel performance may also be affected by air temperature and movement within the underground space.<br /><br />Thermal activation can induce additional stresses and displacements, so structural integrity must be considered. Monitoring data, available mainly for energy piles, indicates stresses of approximately 50–300 kPa per °C and head displacements of 0.01–0.15 mm per °C; the authors consider these effects generally manageable with appropriate design.<br /><br />Available evidence suggests operating systems can achieve payback periods of four to eight years and reduce CO₂ emissions. Overall, energy geostructures offer a practical, potentially cost-effective low-carbon heating and cooling option, provided designers account for site conditions, structural constraints and long-term system control.

Keywords

energy geostructures

energy piles

energy walls

energy tunnels

ground heat exchangers

geothermal heating and cooling

heat pump systems

renewable energy

thermal performance

carbon emissions reduction