Study on heat transfer performance of geothermal pile-foundation heat exchanger with 3-U pipe configuration

Abstract

Targeting the heat transfer performance of geothermal pile-foundation heat exchanger in ground source heat pump system (GSHP), the physical models of 3-U pile-foundation heat exchanger and heat exchanger group were established. CFD software was used to simulate heat transfer processes and heat transfer performance was analyzed both in cooling and heating mode. The simulation results indicated that the higher thermal conductivity of pile-foundation heat exchanger contributed to the higher heat transfer efficiency than soil. Heat transfer flux per meter of the pile-foundation heat exchanger gradually decreased with time went on. After operating for ten years, the average soil temperature increased by 2.96 K in non-equilibrium condition and decreased by 0.61 K in equilibrium condition. The equilibrium condition of cooling and heating load was beneficial to operation system's safety and efficiency. The experimental values of temperature differences were 2.2 K, 2.5 K and 3.5 K, and the heat transfer flux were stable at 58.1 W·m − 1, 65.9 W·m − 1 and 46.2 W·m − 1 in three schemes separately. The maximum difference value was 8.4% for temperature difference between experiment and simulation. The simulation results corresponded well with experimental data, indicating the reliability of simulation. The study results were approximate to the actual situation and can be used as theoretical basis for design and application of pile-foundation heat exchanger in GSHP system.