Long-Term Performance and Sustainable Operation of Energy Piles

Ground temperatures below a depth of about 6 meters (20 feet) remain stable compared to outside air temperatures. This relatively constant temperature and the thermal storage capacity of the ground can be exploited for heating and cooling of buildings. Traditionally, geothermal boreholes have utilized this concept for space heating and cooling. Recently, this ground coupling concept has been expanded from geothermal borehole systems to the use of building foundation elements as heat exchangers. In this hybrid system, geothermal loops are integrated into the deep foundation elements, such as piles, piers, or drilled shafts, that are already in place to provide structural support. The loop is connected to a geothermal heat pump as the heat energy is fed into the ground for cooling in the summer and withdrawn from the ground for heating in the winter. Because geothermal heat pumps use the ground as a constant temperature source which serves as a more favorable baseline compared to the ambient air temperature, these systems work much more efficiently for space heating and cooling compared to air-sourced heat pumps. Sustainable use of the ground as a renewable energy source depends on the seasonal energy load balance. This paper presents the findings on the long-term performance energy piles and their efficiency as heat exchange elements within areas where the demand is non-symmetrical.