A Review of Thermal Response Test Analysis Using Pumping Test Concepts

Abstract

The design of ground-coupled heat pump systems requires knowledge of the thermal properties of the subsurface and boreholes. These properties can be measured with in situ thermal response tests (TRT), where a heat transfer fluid flowing in a ground heat exchanger is heated with an electric element and the resulting temperature perturbation is monitored. These tests are analogous to standard pumping tests conducted in hydrogeology, because a system that is initially assumed at equilibrium is perturbed and the response is monitored in time, to assess the system's properties with inverse modeling. Although pumping test analysis is a mature topic in hydrogeology, the current analysis of temperature measurements in the context of TRTs is comparatively a new topic and it could benefit from the application of concepts related to pumping tests. The purpose of this work is to review the methodology of TRTs and improve their analysis using pumping test concepts, such as the well function, the superposition principle, and the radius of influence. The improvements are demonstrated with three TRTs. The first test was conducted in unsaturated waste rock at an active mine and the other two tests aimed at evaluating the performance of thermally enhanced pipe installed in a fully saturated sedimentary rock formation. The concepts borrowed from pumping tests allowed the planning of the duration of the TRTs and the analysis of variable heat injection rate tests accounting for external heat transfer and temperature recovery, which reduces the uncertainty in the estimation of thermal properties.

Geophysical Methods for Monitoring Temperature Changes in Shallow Low Enthalpy Geothermal Systems

“…Figure 9 compares the observed behavior during the test and the expected behavior according to Equation (13). Up to 30 °C, the increase in conductivity is coherent with the proposed law.…”

“…However, such models require the knowledge of the parameters governing groundwater flow (e.g., hydraulic conductivity and specific storage) and heat transport (e.g., thermal conductivity, volumetric heat capacity, flow rate). In situ tests, such as thermal response tests [12,13] or laboratory measurements [14] are sometimes possible, but the values obtained may deliver only well-centered information or may not always (if not at all) be representative of in situ conditions at a larger scale. Such data are often scarce if not missing and authors often have to rely on standard calculation charts, values found in the literature, or simply default values implemented in standard software (e.g., [15][16][17][18]).…”

Comparison of two different models for pile thermal response test interpretation

“…For the line source, the absence of the qR b term in Equation 11 means that the model is forced through the origin, when potentially there may still be some power applied due to the operation of the circulation pump, and/or due to other external influences. Recovery data are traditionally viewed as more reliable than heat injection data due to the absence of power supply variations and the fact that g can be determined independently of R b [49]. However, it comes with the disadvantage of increased test costs.…”

Development of TPRT (Thermal Performance-Response Test) for Borehole Heat Exchanger Design

“…In addition to examining the performance of complex shape GHEs, TPTs can also be used to examine the actual performance of an installed conventional BHE. Obtaining the heat exchange rate is important because many uncertainties affect the construction and design of BHEs, such as the geometry of the U-tubes (torsion and bending of pipe legs), uneven packing of the grouting or backfill, unverified subsurface heat-transfer phenomena, and uncertain ground properties, as noted in Bernier (2002) ;Raymond, et al (2011);Spitler and Gehlin (2015); Witte (2013).…”