Innovative Methodology to Compute the Temperature Evolution of Pile Heat Exchangers

International audienceEnergy geostructures such as heat exchanger piles couple the structural role of geostructures with heat and cold supply via shallow geothermal energy. This combination makes it possible to cut down the investment costs of ground heat exchangers (GHE). Thermal dynamic simulations require numerical models of pile heat exchangers to run over a reasonable amount of time. In this perspective semi-analytical models seem interesting. The paper presents an approach to semi-analytical modeling of pile heat exchangers. This approach relies on three elements: First, correlations are established to describe the evolution of wall pipe temperature under constant heat load in presence of underground water flow. These correlations take into account the underground water flow in the vicinity of the pile, allowing the computation of the temperature evolution over both the short and long terms. Second, a resistive-capacitive (RC) circuit is developed to account for the thermal inertia of the pile concrete without having to mesh its geometry. Third, the RC circuit is combined to a heat balance over the heat carrier fluid and to correlations to compute temperature evolution in the fluid. Predictions of this semi-analytical model are compared with those of a fully-discretized finite elements model. A good agreement between both models is reached. Acquisition of in-situ data is foreseen to validate both models