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Energies 2016, 9(11), 890; doi:10.3390/en9110890

Dimensionless Maps for the Validity of Analytical Ground Heat Transfer Models for GSHP Applications

1
BETTER—Building Energy Technique and Technology Research Group, University of Pisa, Largo Lucio Lazzarino, Pisa 56122, Italy
2
DESTEC—Department of Energy, Systems, Territory and Constructions Engineering, University of Pisa, Largo Lucio Lazzarino, Pisa 56122, Italy
Academic Editor: Rajandrea Sethi
Received: 13 August 2016 / Revised: 3 October 2016 / Accepted: 24 October 2016 / Published: 29 October 2016
(This article belongs to the Special Issue Low Enthalpy Geothermal Energy)
View Full-Text   |   Download PDF [2311 KB, uploaded 29 October 2016]   |  

Abstract

This article provides plain and handy expressions to decide the most suitable analytical model for the thermal analysis of the ground source in vertical ground-coupled heat pump applications. We perform a comprehensive dimensionless analysis of the reciprocal deviation among the classical infinite, finite, linear and cylindrical heat source models in purely conductive media. Besides, we complete the framework of possible boreholes model with the “hollow” finite cylindrical heat source solution, still lacking in the literature. Analytical expressions are effective tools for both design and performance assessment: they are able to provide practical and general indications on the thermal behavior of the ground with an advantageous tradeoff between calculation efforts and solution accuracy. This notwithstanding, their applicability to any specific case is always subjected to the coherence of the model assumptions, also in terms of length and time scales, with the specific case of interest. We propose several dimensionless criteria to evaluate when one model is practically equivalent to another one and handy maps that can be used for both design and performance analysis. Finally, we found that the finite line source represents the most suitable model for borehole heat exchangers (BHEs), as it is applicable to a wide range of space and time scales, practically providing the same results of more complex models. View Full-Text
Keywords: ground-source heat pump systems; ground heat transfer; analytical models; infinite linear heat source; infinite cylindrical heat source; finite linear heat source; finite cylindrical heat source; purely-conductive media; dimensionless analysis ground-source heat pump systems; ground heat transfer; analytical models; infinite linear heat source; infinite cylindrical heat source; finite linear heat source; finite cylindrical heat source; purely-conductive media; dimensionless analysis
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Conti, P. Dimensionless Maps for the Validity of Analytical Ground Heat Transfer Models for GSHP Applications. Energies 2016, 9, 890.

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