Interpretation of Thermal Response Tests in Borehole Heat Exchangers Affected by Advection

Abstract

We focus on the treatment of thermal response test data when both advection and short-period changes of surface temperature occur. We used a moving line source model to simulate temperature-time signals under an advective thermal regime. The subsurface thermal conductivity, the Darcy velocity and the borehole thermal resistance were inferred by means of an optimisation procedure. In case of Darcy velocity lower than 10-7 m s-1, the underground thermal conductivity is comparable to that obtained by means of the infinite line source model, which assumes a purely conductive thermal regime. The optimisation analysis was finally applied to real thermal response test data. The temperature-time curves were filtered to remove the disturbing spectral components associated to a non-optimal thermostatic behaviour of the apparatus. This produced reliable estimates of thermal and hydraulic parameters. An independent method based on the analysis of temperature-depth logs was used to validate the inferred groundwater flow.