Influences of ground saturation and thermal boundary condition on energy harvesting using geothermal piles

The paper highlights an important distinction between heat transfer mechanism in dry and saturated soil. The effects of two site-specific conditions (e.g., soil saturation and thermal insulation at ground surface) on pile-soil heat exchange and ground temperature response are investigated through a series of thermal tests under laboratory-controlled conditions. Soil temperature data recorded during model tests are compared with soil thermal response predicted using a numerical pile-soil heat exchange model. Moreover, effective thermal conductivity values for the pile-soil system are derived employing equivalent line source model that utilizes circulation fluid temperature recorded during the laboratory tests. Such derived effective thermal conductivity values are compared with soil thermal conductivity values obtained from element thermal conductivity tests. Analysis of recorded soil temperature data and readings from pore pressure transducers during the thermal loading tests identify the possibility of temperature-induced pore fluid flow and convective heat transfer in saturated soil surrounding a ground heat exchanger.