The impact of heat exchanger loop configuration on heat transfer in energy piles

This paper examines the impact of parallel and series U-loop configurations on heat transfer in energy piles. Heating experiments were conducted on a set of four field-scale energy piles installed under a five-storey building, sharing identical dimensions (diameter = 0.9 m and length = 15 m) but varying numbers of U-loops (loops 1, 2, 3, and 4, in Piles 1, 2, 3, and 4, respectively). The investigation highlights the significance of fluid flow, temperature, U-loop quantity and configuration on heat transfer within solitary and grouped energy piles. In the parallel configuration, heat exchange occurs concurrently across all U-loops, proportional to the flow rate. Conversely, in the series configuration, the initial U-loops dominate heat exchange, with subsequent U-loops showing diminished effectiveness in contributing to the overall heat transfer. For identical flow rates in the individual U-loops of both configurations, the group of energy piles employing parallel U-loops exhibited higher heat exchange. The findings provide practical insights into optimising U-loop configurations to improve heat exchange between the pile and the surrounding soil under the studied boundary conditions.