RENEWABLE ENERGY APPLICATIONS USING THERMO-ACTIVE DEEP FOUNDATIONS

Abstract

Rising energy costs and the adverse effects of carbon emissions have given rise to an increased use of geothermal energy for heating and cooling of structures. Of increasing use in geotechnical engineering practice are thermo-active foundations that contain geothermal loops integrated into structural elements in contact with the ground. Such applications have been developed for shallow and deep foundations, retaining and basement walls, tunnel linings, soil nails, and earth anchors. These structures perform the dual function of providing structural support and exchanging heat with the ground to harness geothermal energy. In particular, the use of Energy Piles, which are thermo-active deep foundation elements such as drilled shafts and driven piles, has grown exponentially in Europe over the past decade, but they have received little attention in the US. Energy Piles contain HDPE tubes filled with glycol-water mixtures which are circulated via a heat pump or cooling machine. Heat energy is injected into and withdrawn from the ground for cooling in the summer and heating in the winter, respectively. Because they are used where pile foundations must be installed anyway, these systems provide the thermal performance of deep geothermal systems without the additional drilling costs. Case studies show they can significantly lower heating/cooling costs and reduce carbon footprint. This paper discusses key geotechnical aspects of Energy Pile design and performance, along with design challenges that must be overcome to promote wider usage of this technology.