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Numerical Evaluation of Long-Term Performance of Borehole Heat Exchanger Fields

A. Priarone[1], S. Lazzari[1], and E. Zanchini[1]

[1]Dipartimento di Ingegneria Energetica, Nucleare e del Controllo Ambientale, Alma Mater Studiorum - Università di Bologna, Bologna, Italy

The long-term performance of double U-tube Borehole Heat Exchangers (BHEs) is studied numerically by considering three different time-dependent heat fluxes exchanged between each BHE and the ground. Since the temperature distribution along the vertical direction has a negligible influence on long-term BHE performance, the problem is studied by means of a 2D conduction model, where the energy transfer due to water flow is replaced by a uniform, time dependent, heat generation. The fluid mean temperature in the BHE is determined as a function of time. Results point out that, in the absence of groundwater movement, when a BHE field is considered, at least a partial compensation of the thermal load is necessary to avoid long-term system breakdown.