Thermal Conductivity Evaluation of a Pile Group Using Geothermal Energy Piles

Thermal conductivity tests were performed on three auger pressure grouted piles, both individually and as a group. These piles were installed with geothermal pipes used for closed loop geothermal heating and cooling applications. Installing pipe loops in piles allows geothermal energy captured from the ground to be transferred using heat pumps to heat and cool buildings. This technology provides both a renewable energy source and a cost effective option compared to other geothermal and conventional methods. The results of the group test are compared to the individual pile results at a site with a soil profile consisting of sand and clay through the depth that the piles were installed. Measurements of the pile temperature, circulating water temperature, and ground temperature in the center of the pile group for the week long group test are presented. The thermal conductivities for all cases are calculated using line source methods. An example energy pile design for a two story office building supported on these piles is also presented.