Thermomechanical Responses of Thermally Interacting Field-Scale Energy Piles

Abstract

This paper explores how energy piles interact under imbalanced and balanced daily temperature cycles and a range of monotonic thermal loads, combining field experiments and numerical simulations on two bored energy piles with a spacing of 3.5 m. Monotonic heating and cooling loads were simulated for temperature changes of |ΔT| = 5°C, 10°C, 15°C, and 20°C. Balanced, cooling-oriented imbalanced, and heating-oriented imbalanced thermal cycles were simulated between 0°C and 40°C with heating-to-cooling time ratios of 12:12, 16:8, and 8:16, respectively. One of the two energy piles’ axial and radial thermomechanical responses was investigated during single- and dual-pile operations. Soil temperature changes between the piles were greater for dual-pile operation, leading to increased thermal interaction, particularly for higher magnitudes of monotonic thermal loads. However, dual-pile operation did not alter the ground temperatures near the edge of the piles for the pile spacing considered. They remained similar for single- and dual-pile operations for the setting investigated in this paper. As a result, the pile temperatures, axial and radial thermal stresses, and thermal stress rates were similar for all single- and dual-pile operations simulations. Cyclic temperatures, particularly balanced cyclic loads, induced lower thermal effects in the piles and soil than in other cases. Overall, the results from this study provide validated insights into the situations where thermal interaction and different temperatures typical of heat pumps should be considered in designing groups of energy piles.