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Virtual borehole for thermal response test unit calibration: Test facility and concept development

Nejad, Parham Eslami
Badache, Messaoud
Corcoran, Alexia
Bernier, Michel
Precise calculation of the borehole length requires good estimation of the ground thermal conductivity. In practice, the ground thermal conductivity is measured in-situ at a specific location using what is referred to as a thermal response test (TRT) unit. This paper presents a novel virtual borehole (VB) concept for calibrating TRT units. The VB replaces a real borehole with an above-ground compact heat exchanger and a chiller unit to mimic the thermal behavior of the ground with a user-set virtual ground thermal conductivity. In an attempt to develop the VB concept, three control scenarios are examined to emulate the ground thermal response for different thermal conductivity values. A test bench was built at the CanmetENERGY-Varennes research laboratory to validate the VB concept experimentally. A test is performed to calibrate a commercially available TRT unit for a thermal conductivity value of 3 W m-1 K-1. The TRT unit connected to the VB reported a value of 3.18 W m-1 K-1 representing a 6% error.