Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Estimation of In-Situ Heat Capacity and Thermal Diffusivity from Undisturbed Ground Temperature Profile Measured in Ground Heat Exchangers.

Version 1 : Received: 10 March 2022 / Approved: 14 March 2022 / Online: 14 March 2022 (03:34:10 CET)

A peer-reviewed article of this Preprint also exists.

Pambou, C.H.K.; Raymond, J.; Miranda, M.M.; Giordano, N. Estimation of In Situ Heat Capacity and Thermal Diffusivity from Undisturbed Ground Temperature Profile Measured in Ground Heat Exchangers. Geosciences 2022, 12, 180. Pambou, C.H.K.; Raymond, J.; Miranda, M.M.; Giordano, N. Estimation of In Situ Heat Capacity and Thermal Diffusivity from Undisturbed Ground Temperature Profile Measured in Ground Heat Exchangers. Geosciences 2022, 12, 180.

Journal reference: Geosciences 2022, 12, 180
DOI: 10.3390/geosciences12050180

Abstract

Undisturbed ground temperature (UGT), thermal conductivity (TC) and heat capacity (HC) are essential parameters for the design of borehole heat exchanger (BHE) and borehole thermal energy storage systems. However, field methods to assess the thermal state and properties of the sub-surface are costly and time consuming. Moreover, HC is often not evaluated but arbitrarily selected from literature considering the geological materials intercepted by boreholes. Therefore, this work aims at proposing a field heat tracing method to infer the thermal diffusivity (TD) and HC with assumption of natural transient heat conduction in the subsurface. Empirical equations were developed to reproduce a UGT profile measured along a BHE. Experimental coefficients are found with a non-linear least square solver optimization and used to calculate the damping depth and TD. Subsequently, the TD is used to evaluate HC considering TC obtained from a thermal response test (TRT). Results from this proposed heat tracing method were verified and validated against a set of TRT results and oscillatory TRT analysis using a field dual probe concept to infer HC. The example here described highlights the advantages and novelty of this fast and simple field method relying only on a single UGT profile measured before a TRT.

Keywords

heat conduction; thermal properties; geothermal heat pump; damping depth

Subject

EARTH SCIENCES, Geology

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