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

Abstract

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.