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Determination of Vertical Borehole and Geological Formation Properties using the Crossed Contour Method



Brian P. Leyde, S. A. Klein, G. F. Nellis, Harrison Skye


This paper presents a new method called the Crossed Contour Method for determining the effective properties (borehole radius and ground thermal conductivity) of a vertical ground-coupled heat exchanger. The method has been applied to both simulated and experimental borehole Thermal Response Test (TRT) data using the Duct Storage vertical ground heat exchanger model implemented in the TRansient SYstems Simulation software (TRNSYS). The Crossed Contour Method generates a parametric grid of simulated TRT data for different combinations of borehole radius and ground thermal conductivity in a series of time windows. The error between the simulated and experimental bore field outlet temperature is calculated for each set of borehole properties within each time window. Using these data, contours of the minimum error are constructed in the parameter space of borehole radius and ground thermal conductivity. When all of the minimum error contours for each time window are superimposed, the point where the contours cross (intersect) identifies the effective borehole properties for the model that most closely represents the experimental data in every time window and thus over the entire length of the experimental data set. The computed borehole properties are compared with results from existing model inversion methods including the Ground Property Measurement (GPM) software developed by Oak Ridge National Laboratory, and the Line Source Model. The Crossed Contour method was used to determine the effective formation conductivity and borehole radius of several TRT data sets generated at the National Institute of Standards and Technology's Net Zero Energy Residential Test Facility (Davis et al. 2014, Fanney et al. 2014). The same data sets were also analyzed using the line source model, Oak Ridge National Labs GPM software (Shonder and Beck, 1997), and an alternative parameter optimization technique applied to the same core TRNSYS model (the DST model) that is used for the Cr


Thermal Response Test, Ground Property Measurement, Parameter Estimation, Ground Thermal Conductivity, Ground Loop Heat Exchangers, TRNSYS Optimization, Geothermal


Leyde, B. , Klein, S. , Nellis, G. and Skye, H. (2017), Determination of Vertical Borehole and Geological Formation Properties using the Crossed Contour Method, Geothermics, [online],, (Accessed October 23, 2021)
Created January 8, 2017, Updated October 12, 2021