Thermal performance of pipe-type energy piles with open-ended heat exchange tubes

This paper examines the thermal performance of pipe-type energy piles with open-ended heat exchange tubes (abbreviation as: open-tube energy pile). This study compares the thermal performance of U-tube energy piles with open-tube energy piles through model testing. The analysis focused on heat exchange efficiency, temperature changes at inlet and outlet points, and the piles’ and surrounding soil's temperature response characteristics. An analytical model using Laplace transform was developed for the open-tube energy pile, with simulations conducted to analyze it at full scale. Results indicate that, under the same cases, the open-tube energy pile exhibits higher heat exchange efficiency than the U-tube energy pile. Additionally, the pile and surrounding soil show more pronounced temperature responses during testing with the open-tube configuration. Compared to existing models, the heat transfer model proposed in this paper is more suitable for analyzing the heat transfer of open-tube energy pile. Moreover, changes in the thermophysical properties of the pipe pile and soil will have different effects on the heat transfer between the pile and the soil.