Selection of the design temperature change for energy piles

This paper presents a simplified procedure to approximate the temperature change for energy pile design. Depending on the proximity from the heat exchange loops, various locations within the cross-section of an energy pile are subjected to different magnitudes of temperature changes throughout the operational lifetime of the pile. Despite this non-uniform temperature change within the pile, any pile cross-section undergoes a uniform thermal strain or displacement. First, this paper presents a simplified stress analysis to approximate the temperature change corresponding to the observed uniform thermal stains. The results of this stress analysis proves that the uniform observed thermal stains correspond to the average temperature change over the pile cross-section. Thus, the average temperature change over the pile section is recommended for the design of energy piles. Second, this study presents a simplified analytical solution, based on the finite line source model, to approximate the average temperature change in any energy pile. The proposed analytical solution is validated against finite element numerical models for energy piles with various sizes and different number of heat exchange loops. This proposed approximation shows reliable results eliminating the need to use complicated numerical models saving computational time and cost.