Ground thermal conductivity estimation using the thermal response test with a horizontal ground heat exchanger

Abstract

The thermal response test (TRT) is a highly developed and widespread method for measuring ground thermal conductivity using ground source heat exchangers (GHEs). However, its application is mostly limited to vertical ground heat exchangers (VGHEs), with very few previous studies on TRT with horizontal configurations. Therefore, the objective of this article is to evaluate the applicability of TRT for estimating the ground thermal conductivity with horizontal ground heat exchangers (HGHEs) at shallow depths. The short duration of the TRT prevents thermal interference between the ground surface and the horizontal heat exchanger, allowing the use of the same equation to calculate the ground thermal conductivity with VGHEs and HGHEs. This advantage is not presented when evaluating the long-term performance of GHEs, a procedure that is generally more complex in horizontal systems. For the test, the HGHE consisted of a straight HDPE pipe arranged in a U-shape (depth 2.5 m, length 36 m). The effective ground thermal conductivity obtained with the TRT has a value of 0.72W/m·K. This result is in good agreement with the thermal conductivity values of sandy loam, the type of soil at the test site.