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Subproject 1.3

Analysis and optimisation of of short time-backfill-check TRTs and other innovative BHE measurement methods

Lead Management
Subproject Leader
Dr. Roman Zorn (
Participating Partners
Burkhardt GmbH
Fraunhofer ISE
Hauri KG
H.S.W. GmbH
ZAE Bayern

The validity of short-time-backfill-check thermal response tests (TRTs) can only be adequately evaluated if a systematic and holistic thermal characterisation of the borehole heat exchanger system is carried out. This is done in a holistically and systematically manner for the first time in this project by measuring the heat capacity and thermal conductivity of all common backfill materials and selected rocks under defined boundary conditions.

A modified short-time-backfill-check TRT is tested on borehole heat exchangers at the quarry of the Hauri company by simultaneously carrying out depth-oriented temperature measurements in combination with trace measurements in each pipe of the U-tubes during the cooling phase and thus achieving a three-dimensional temperature measurement field (active thermal tomography). Using the spatial resolution, it is possible to resolve thermal anomalies and thus, potentially increase the informative value of short-time-backfill-check TRTs. A validation of the measurement results of the short-time-backfill-check TRT is carried out by exposure of the borehole heat exchangers from the subsurface with subsequent detailed analysis of the samples in the laboratory. Based on the results of the investigations, theoretical models for the analysis and evaluation of the short-time-backfill-check are carried out.

Another important goal of this project is to assess the quality of the backfilling of borehole heat exchangers. For this purpose, the ultrasonic probe developed in the predecessor project QEWS II is tested on several test boreholes under practical conditions. Since a single geophysical investigation method is not sufficient for reliable conclusion on the backfilling quality, especially under sensitive geological conditions, a novel, miniaturised thermal borehole packer system is developed, which uses the TRT principle.
Project Partners
Funding Authority