The annual fluctuation of underground temperature response caused by ground heat exchanger in the condition of groundwater seepage

Groundwater seepage plays a role in the heat transfer between ground heat exchanger (GHE) and the surrounding underground medium, and the heat transfer mode is converted from conduction to combined case containing both conduction and convection, which means groundwater seepage inevitably exerts influence on the underground temperature response caused by GHE. The paper describes the equations of underground temperature response while groundwater flows through GHE by means of three-dimensional velocity, and this is the new knowledge differing from traditional one-dimensional velocity. The dimensionless method is employed to conveniently express the formulas; the temperature fields around GHE are investigated to show the influence of groundwater seepage, and the comparisons between without and with groundwater seepage are made. Afterwards, the underground temperature variations of different conditions are analyzed, some stages including cooling period, heating period and transitional period are adopted to analyze the corresponding temperature variations, and the influencing factors for annual underground temperature variation are discussed. In addition, the angles of seepage direction are illustrated, and the temperature response of one location can be changed with the angles. The researches of the paper are novel for further understanding the groundwater seepage. (C) 2019 Elsevier B.V. All rights reserved.