Conductive heat transfer analysis of energy pile

In the range of vertical ground heat exchanger borehole and energy pile, heat is diffused from the heat pipes into the concrete and then to the surrounding soil. The heat transfer process usually follows three main mechanisms: conduction, convection and radiation. Among them, the heat conduction due to temperature gradient is the most relevant process associated with heat transfer in soil and pile. The review of conduction heat transfer models applied to vertical heat exchanger borehole and energy pile shows that the existing models can be classified into two groups, the first one is applied in homogeneous media and the second one is applied in composite media. Most of these models are generally suitable for the case of steady state conduction of heat exchanger boreholes. However, energy pile foundation has larger diameter and smaller length than that of the borehole. As a result, heat transfer inside the pile will take a longer time to reach the steady state. In this paper, a new solution of conductive heat transfer based on the transient heat model is presented. This solution is applied for energy pile and is validated by using the solution of finite element method.