Soil effective thermal conductivity from energy pile thermal tests

The concept of transferring heat from a lower temperature circuit to a higher temperature circuit utilising a heat transfer mechanism has been around for centuries. Recently, this concept has been extended to pile foundations where the piles act as heat exchangers (energy piles) to extract from or store energy in the ground. For these systems to operate efficiently, it is necessary to select suitable design methods and tools to assess their thermal behaviour. An optimised system design requires the understanding of the built structure energy (secondary circuit) requirement. However, an understanding of the relationship between temperature transfer of the surrounding ground to and from the heat exchanger (primary circuit) is critical. As the knowledge of the thermal process in the ground and its interaction with the heat exchanging energy pile are needed to determine the amount of energy that can be extracted from or stored in to the ground. This paper reviews the concept of utilising the primary circuit to assess the ground thermal properties and presents the effective thermal conductivity results obtained from in-situ thermal response tests carried out on a field energy pile.