Investigation of microencapsulate phase change material-based energy pile group: Energy analysis and optimization design

Abstract

Energy piles have attracted increasing interest for bearing structural loads and providing energy for space conditioning by employing geothermal energy from a ground source heat pump system. Although energy piles have demonstrated promise for geothermal energy exploitation, the insufficient energy supply resulting from geotechnical design prohibits their broad deployment. To address the incompetency of energy piles, we propose an innovative design of high-energy efficiency energy pile group by incorporating microencapsulated Phase Change Material (microPCM) into energy piles. With experimental measurement and numerical simulation, a systematic evaluation of the microPCM energy pile group is carried out, from property characterization to energy performance analysis. In addition, the influences of GHE configurations (U shape, W shape, and double U shape) and microPCM addition ratios on energy-saving potential and optimal design of the microPCM energy pile group in cooling mode are investigated. The results reveal the great potential of adding microPCM to facilitate more energy extraction for the energy pile group. However, because the addition of microPCM degrades the compressive strength of the energy pile, it is recommended to increase the concrete design grade when employing microPCM energy piles in engineering practice. In addition, the energy pile with double U shape GHE and 1% wt. microPCM addition is identified as the optimal design in the study, which contributes to 6–49% more energy extraction with a tolerable loss in compressive strength. Meanwhile, the separation spacing between adjacent piles should be greater than 3D to prevent thermal interactions and ensure stable energy performance. This study aims to provide support for the optimal design of the microPCM energy pile group and guide its engineering application.