Finite-Element Modeling of Heat Transfer in Ground Source Energy Systems with Heat Exchanger Pipes

Ground source energy systems (GSES) utilize low enthalpy geothermal energy and have been recognized as an efficient means of providing low carbon space heating and cooling. This study focuses on GSES where the exchange of heat between the ground and the building is achieved by circulating a fluid through heat exchanger pipes. Although numerical analysis is a powerful tool for exploring the performance of such systems, simulating the highly advective flows inside the heat exchanger pipes can be problematic. This paper presents an efficient approach for modeling these systems using the finite-element method (FEM). The pipes are discretized with line elements and the conductive-advective heat flux along them is solved using the Petrov-Galerkin FEM instead of the conventional Galerkin FEM. Following extensive numerical studies, a modeling approach for simulating heat exchanger pipes, which employs line elements and a special material with enhanced thermal properties, is developed. The modeling approach is then adopted in three-dimensional simulations of two thermal response tests, with an excellent match between the computed and the measured temperatures being obtained.