Thermo-energy performance of neighbouring energy piles

Abstract

Energy piles are often closely spaced such that the thermal response of one pile might affect the response of neighbouring piles through heat transfer in the soil. This paper examines the changes in extracted energy and ground temperature of two cast-in-place bored energy piles installed below a six-storey building, with a diameter of 0.6 m, length of 10 m and 3.5 m centre-to-centre distance. Field experiments were conducted on singular and dual piles for cooling and cyclic temperatures, continuous daily operation of the ground source heat pump (GSHP) and intermittent cyclic operations with stoppage-to-operating ratios of 2:1 and 1:2. Compared to single pile operations, greater energy was extracted from dual piles for all operating modes despite thermal interaction through the soil volume between the dual piles. The larger stoppage-to-operating ratio of the GSHP induced lower pile and ground temperature changes and higher energy extraction than continuous operation for single and dual pile operations. The larger stoppage-to-operating ratio of the GSHP reduced the thermal interaction between the dual piles by imposing lower ground temperature changes compared to continuous operation. The results demonstrate the practical significance of managing the GSPHs operating modes for optimal thermal performance of multiple closely spaced energy piles.