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Relation Between Mean Fluid Temperature and Outlet Temperature for Single U-Tube Boreholes

Author

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  • Aminhossein Jahanbin

    (Department of Industrial Engineering, Alma Mater Studiorum University of Bologna, Viale Risorgimento 2, 40136 Bologna, Italy)

  • Claudia Naldi

    (Department of Industrial Engineering, Alma Mater Studiorum University of Bologna, Viale Risorgimento 2, 40136 Bologna, Italy)

  • Enzo Zanchini

    (Department of Industrial Engineering, Alma Mater Studiorum University of Bologna, Viale Risorgimento 2, 40136 Bologna, Italy)

Abstract

Ground-coupled heat pump (GCHP) systems usually utilize buried vertical heat exchangers, named borehole heat exchangers (BHEs). The accurate design or simulation of a GCHP system requires the calculation of the time-dependent outlet temperature from the BHEs, T out . However, the most widely employed BHE simulation models yield the time evolution either of the mean temperature of the BHE-ground surface, T sm , or of that of the fluid, T fm . In transient regime, it is not easy to relate T out to either T sm or T fm . In this paper we determine, through 3D finite element simulations, simple expressions of a dimensionless coefficient φ allowing the calculation of T out by means of a simulation model that yields T fm . These expressions hold for single U-tube BHEs, both in quasi-steady and in unsteady working conditions. We validate our 3D simulation code by comparison with an analytical BHE model. Then, we present applications of our expressions of φ to calculate the time-dependent values of T out through a BHE model that yields those of T fm . Finally, we show that the values of φ in quasi-steady working conditions can be used for a simple calculation of the effective borehole thermal resistance.

Suggested Citation

  • Aminhossein Jahanbin & Claudia Naldi & Enzo Zanchini, 2020. "Relation Between Mean Fluid Temperature and Outlet Temperature for Single U-Tube Boreholes," Energies, MDPI, vol. 13(4), pages 1-23, February.
    • Handle: RePEc:gam:jeners:v:13:y:2020:i:4:p:828-:d:320603
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    References listed on IDEAS

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    1. Claudia Naldi & Aminhossein Jahanbin & Enzo Zanchini, 2021. "A New Estimate of Sand and Grout Thermal Properties in the Sandbox Experiment for Accurate Validations of Borehole Simulation Codes," Energies, MDPI, vol. 14(4), pages 1-25, February.
    2. Aminhossein Jahanbin & Giovanni Semprini & Andrea Natale Impiombato & Cesare Biserni & Eugenia Rossi di Schio, 2020. "Effects of the Circuit Arrangement on the Thermal Performance of Double U-Tube Ground Heat Exchangers," Energies, MDPI, vol. 13(12), pages 1-19, June.

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