Study on heat transfer of pile foundation ground heat exchanger with three-dimensional groundwater seepage

An increasing number of high-rise buildings are being designed, enabling the use of pile foundation to also act as ground heat exchangers (GHEs) of ground source heat pumps (GSHPs). These so-called energy piles include heat exchange pipes already cast into the pile foundation to produce a new type of GHE. Groundwater seepage, by means of advection, plays an important role in improving the heat transfer performance of energy pile. Existing research has studied heat transfer mechanism of energy pile when groundwater is considered to flow in one direction only, and in two directions also. No studies, however, have been introduced explaining the effects of three-dimensional (3-D) groundwater seepage (i.e. in three directions) on the heat transfer between pile and underground medium. This paper presents a new mathematical model about the heat transfer of energy pile with 3-D groundwater seepage, whereby the analytical temperature responses solutions induced by both infinite and finite models are obtained. Comparisons between pure conduction and combined heat transfer were made, and the temperature distributions in a 3-D seepage environment are explained. In addition, the characteristics involved in the new model were explored and then the factors exerting influence on heat transfer are described. The 3-D groundwater seepage is more advanced and realistic, and the research described in this paper is usefully relevant to promoting the development of energy piles of GSHP. (C) 2016 Elsevier Ltd. All rights reserved.