Thermal analysis of vertical ground exchangers of heat pumps

Heat flow rate transferred from the ground by vertical ground exchangers of heat pump units is analysed in the paper. The investigation of the mentioned heat flow rate, for different arrangements of the exchanger tubes, different values of the temperature of an intermediate medium, different thermal parameters of the ground, and for the different values of seepage velocity, is the main aim of the paper. For this purpose, proper unsteady state temperature distributions in the ground surrounding the ground exchanger have been calculated. The temperature distributions in the ground considered are governed by the standard unsteady heat conduction equation with the convective term in the unfrozen part of the domain, if the seepage is taken into account, and Stefan's boundary condition on the phase change interface. Calculations have been carried out using the home code FEMCONV, if the seepage is considered. The finite element method (FEM) is implemented in this code both to calculate the temperature fields and the velocity fields of moisture. The Darcy’s model is assumed to describe the seepage flow in the ground. Due to the existence of phase change on the moving interface, the apparent heat capacity method is applied. Additionally, an original technique is used to avoid remeshing because the seepage flow takes place within the unfrozen part of the computational domain, which changes its shape in the time. PATRAN –THERMAL code has been usually employed to calculate the temperature fields in case the seepage is neglected.