Effective Thermal Conductivity and Borehole Thermal Resistance in Selected Borehole Heat Exchangers for the Same Geology

Tomasz Sliwa, Patryk Leśniak, Aneta Sapińska-Śliwa and Marc A. Rosen
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Tomasz Sliwa: Laboratory of Geoenergetics, Drilling, Oil and Gas Faculty, AGH University of Science and Technology, Al. Mickiewicza 30, 30-059 Krakow, Poland
Patryk Leśniak: Laboratory of Geoenergetics, Drilling, Oil and Gas Faculty, AGH University of Science and Technology, Al. Mickiewicza 30, 30-059 Krakow, Poland
Aneta Sapińska-Śliwa: Laboratory of Geoenergetics, Drilling, Oil and Gas Faculty, AGH University of Science and Technology, Al. Mickiewicza 30, 30-059 Krakow, Poland
Marc A. Rosen: Faculty of Engineering and Applied Science, Ontario Tech University, Oshawa, ON L1G 0C5, Canada

Energies, 2022, vol. 15, issue 3, 1-29

Abstract: Investigating the constructions of borehole heat exchangers with high efficiency (unit heat transfer between the heat carrier and ground) is important. One of the means to improve efficiency is the use of the most efficient construction of the borehole heat exchanger. The paper describes research on borehole heat exchangers’ thermal efficiency, which is mainly characterized by parameters obtained from a thermal response test: effective thermal conductivity and borehole thermal resistivity. The borehole heat exchangers of the Laboratory of Geoenergetics in Poland were studied. Based on thermal response test interpretation and empirical equations, one of which is proprietary, the heat transfer is calculated independent of the duration of the thermal response test. Other conditions for using borehole heat exchangers in downtowns are discussed. The research aims to determine the best borehole heat exchanger design from five basic possibilities studied. A lack of unequivocal statements regarding this matter in the literature was observed. The influence of the interpretation method on the research results is determined. A single U-tube system filled with gravel is shown to be the most advantageous design by a very small margin. The applied interpretation methods, however, confirm the hitherto ambiguity in the selection of the best construction. The maximum heat carrier temperature at the end of thermal response tests was 32 °C for a geological profile mostly made up of clay (low thermal conductivity) and 23 °C for Carpathian flysch (sandstones and shales, with a higher value of conductivity).

Keywords: borehole heat exchanger; geothermal heat; borehole thermal resistance; geoenergetics; geothermal heat pump; thermal response test (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2022
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (2)

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