Un-stationary thermal analysis of the vertical ground heat exchanger within unsaturated soils

Daniel Sławiński

Renewable Energy, 2020, vol. 151, issue C, 805-815

Abstract: The efficiency of heat exchange in ground heat exchangers (GHE) in many projects decreases throughout their service life. Large temperature fluctuations were observed during the ground heat exchanger loading and during its natural cooling. This problem stems mainly from the influences of heating and humidity migration on the operation of the ground heat exchanger in unsaturated soil. To find the answer to the problem numerical model of a porous medium with multi-component fluid flow was applied. The mathematical description was expanded by additional streams describing the exchange of thermal energy within the backfill material and the structure of the porous model. Ground porosity was mapped geometrically and mathematically. The definition of total temperature was introduced. The results obtained from proposed model were compared with another model results which was based on solving only the classical heat exchange equation. The model was also verified through the measurement data read from 3 sensors installed at different depths of one borehole and at different time intervals. The parameters of the model result from local climatic conditions of Jabłonna near Warsaw. 24-hour operation of a single borehole was simulated numerically. The results of the model proposed by the author were of a greater convergence with the real data than those obtained for the classical heat exchange model. The critical point of the model was the selection of the coefficients describing the flow resistance of i-components in the porous medium and the particular terms of the total temperature adopted definition. The proposed model allows for a more accurate estimation of the available thermal power in the future and more accurate analysis of the degree of the effort of the structure in the context of its exploitation and the destruction time.

Keywords: Ground heat exchanger; Unsaturated porous medium; Dry soil; Total temperature; Computational fluid dynamics (search for similar items in EconPapers)
Date: 2020
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Persistent link: https://EconPapers.repec.org/RePEc:eee:renene:v:151:y:2020:i:c:p:805-815

DOI: 10.1016/j.renene.2019.11.065

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