Heat transfer enhancement of geothermal energy piles

Geothermal energy piles utilize the almost constant ground temperature at shallow depths below the ground surface to heat and/or cool built structures. Heat is extracted from and/or injected into the ground through the use of a heat carrier fluid that flows in pipes attached to the reinforcement cage of the pile foundations. The performance of the energy piles can be improved by enhancing the heat exchange between the heat carrier fluid and the ground. The purpose of this paper is to provide evidence from literature on multidisciplinary methods to improve the thermal properties of elements in a geothermal energy pile. Geometrical optimization such as the number of pipes and their arrangement can be done to reduce the total pile thermal resistance. Nanofluids can be used as the heat carrier fluid to enhance the fluid conductive and convective heat transfer. Highly thermally conductive fillers can be mixed with the pipe material to enhance its thermal conductivity. The thermal properties of the concrete can also be enhanced by adding highly thermo-conductive materials to the concrete mix.