Thermomechanical Responses of Thermally Interacting Field-Scale Energy Piles

Abstract

Energy piles have great potential for improving the heating and cooling performance of new buildings. However, their axial and radial thermo-mechanical behaviour due to thermal interaction between different energy piles through the surrounding soil is not well understood. This paper combines results from field experiments and numerical simulations on two bored energy piles with a centre-to-centre spacing of 3.5 m to investigate how energy piles interact under balanced and imbalanced daily temperature cycles and a range of monotonic thermal loads. One of the two energy piles' axial and radial thermo-mechanical responses were investigated during single and dual pile operation. Cyclic temperature variations of the piles induced lower soil temperature changes and pile thermal stresses than monotonic temperature variations. The balanced cyclic temperatures induced lower thermal effects in the pile and the soil than imbalanced cyclic temperatures. Significant soil temperature changes were recorded between the piles when the two piles were heated to 40°C and cooled to 0°C. However, the pile thermal stresses were similar for single and dual pile operations, indicating that thermal interaction between the piles through the surrounding soil had negligible effects on pile behaviour for the setting investigated in this paper. The piles radial thermal stresses were negligible compared to the axial thermal stresses for all studied cases. Overall, the results from this study provide validated insights into the situations where thermal interaction should be considered in design.