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A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "H: Geo-Energy".

Deadline for manuscript submissions: closed (15 October 2020) | Viewed by 13935

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Special Issue Editors

Dr. Paul Christodoulides

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Guest Editor

Faculty of Engineering and Technology, Cyprus University of Technology, P.O. Box 50329, Limassol 3603, Cyprus
Interests: fluid dynamics; nonlinear and dispersive waves; free surface flows; fluid impacts on structures; energy; heat transfer; microfluidics; applications of dynamical systems; stochastic modeling

Dr. Georgios Florides

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Guest Editor

Cyprus University of Technology, Faculty of Engineering & Technology, Limassol, Cyprus
Interests: energy; heat transfer; climate; dinosaurs

Special Issue Information

Dear Colleagues,

“Computational Geothermal Energy Applications” is the title of a Special Issue of the journal Energies that will serve as a guide for specific problems of Geothermal Energy. It will include the presentation of ideas, methods, and results related to computational fluid dynamics and heat transfer in solids, liquids, and gases, with specific geothermal applications, including heat pumps. All modes of heat and mass transfer, such as conduction, convection, diffusion, radiation, and phase change, will be specifically addressed. This Special Issue will also include discussions on thermodynamic principles, thermal properties of substances, thermal cycles, etc.

The themes of shallow geothermal energy applications, deep geothermal energy, groundwater flow, underground tunnels, underground constructions, and thermal stresses are expected to be addressed. More specifically, this Special Issue will report the development of new mathematical methods and computational algorithms and the application of new or existing methods to the solution of problems in the field under study. Experimental studies in combination with numerical/computational works are expected. The assessment of the accuracy of computational solutions through verification and validation is an essential aspect to be dealt with. Review papers on relevant topics are also invited.

Dr. Paul Christodoulides
Dr. Georgios Florides
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Shallow Geothermal energy
Deep Geothermal Energy
Groundwater flow
Underground constructions
Thermal stresses
Computational methods

Published Papers (5 papers)

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Research

Jump to: Review

22 pages, 3385 KiB

Open AccessArticle

Residential Buildings’ Foundations as a Ground Heat Exchanger and Comparison among Different Types in a Moderate Climate Country

by Lazaros Aresti, Paul Christodoulides, Gregoris P. Panayiotou and Georgios Florides

Energies 2020, 13(23), 6287; https://doi.org/10.3390/en13236287 - 28 Nov 2020

Cited by 7 | Viewed by 1852

Abstract

Shallow Geothermal Energy Systems (SGESs) constitute Renewable Energy Systems (RES), which find application in the residential sector through the use of Ground Source Heat Pumps (GSHPs). GSHPs are associated with Ground Heat Exchangers (GHEs), whereby heat is gained/lost through a network of tubes into the ground. GSHPs have failed to flourish in the RES market due to their high initial costs and long payback periods. In this study, the use of Energy Geo-Structure (EGS) systems, namely, the foundation (or energy) piles and the foundation bed of a residential building in Cyprus, was computationally modeled in the COMSOL Multiphysics software. First, the single-houses’ trend in number of units and area in Cyprus was examined and a theoretically typical house with nearly Zero Energy Building (nZEB) characteristics was considered. The heating and cooling loads were estimated in the TRNSYS software environment and used as inputs to investigate the performance of the GSHP/GHE systems. Both systems were shown to exhibit steady performance and high Coefficient of Performance (COP) values, making them an alternative RES solution for residential building integration. Next, the systems were economically evaluated through a comparison with a convectional Air Source Heat Pump (ASHP) system. The economic analysis showed that the cost of the suggested conversions of the foundation elements into GHEs had short payback periods. Consequently, either using the foundation piles or bed as a GHE is a profitable investment and an alternative to conventional RES. Full article

(This article belongs to the Special Issue Computational Geothermal Energy Applications)

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24 pages, 2452 KiB

Open AccessArticle

Explicit Multipole Formula for the Local Thermal Resistance in an Energy Pile—The Line-Source Approximation

by Johan Claesson and Saqib Javed

Energies 2020, 13(20), 5445; https://doi.org/10.3390/en13205445 - 19 Oct 2020

Cited by 5 | Viewed by 2117

Abstract

This paper presents a closed-form quite handy formula for the local thermal resistance R_b between the temperature of the bulk heat-carrier fluid in the pipes, equally spaced on a concentric circle inside a circular energy pile, and the mean temperature at the periphery of the pile. The so-called multipole method is used to calculate the temperature field. An important improvement of the multipole method is presented, where Cauchy’s mean value theorem of analytical functions is used. The formula for thermal resistance R_b0 for the zero-order approximation (J = 0), where only line heat sources at the pipes are used, is presented. The errors using zeroth-order approximation (J = 0) are shown to be quite small by comparisons with eight-order approximation (J = 8) with its accuracy of more than eight digits. The relative error for the local thermal resistance R_b0 for the zero-order approximation (J = 0) lies below 5% for a wide range of input parameter values. These ranges are judged to cover most practical cases of application. The smallest local thermal resistance R_bmin is, with some exceptions, obtained when the pipes lie directly in contact with the pile periphery. A neat formula for this minimum is presented. Full article

(This article belongs to the Special Issue Computational Geothermal Energy Applications)

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19 pages, 3365 KiB

Open AccessArticle

Effects of the Circuit Arrangement on the Thermal Performance of Double U-Tube Ground Heat Exchangers

by Aminhossein Jahanbin, Giovanni Semprini, Andrea Natale Impiombato, Cesare Biserni and Eugenia Rossi di Schio

Energies 2020, 13(12), 3275; https://doi.org/10.3390/en13123275 - 24 Jun 2020

Cited by 14 | Viewed by 2873

Abstract

Given that the issue of variations in geometrical parameters of the borehole heat exchanger (BHE) revolves around the phenomenon of thermal resistance, a thorough understanding of these parameters is beneficial in enhancing thermal performance of BHEs. The present study seeks to identify relative changes in the thermal performance of double U-tube BHEs triggered by alterations in circuit arrangements, as well as the shank spacing and the borehole length. The thermal performance of double U-tube BHEs with different configurations is comprehensively analyzed through a 3D transient numerical code developed by means of the finite element method. The sensitivity of each circuit configuration in terms of the thermal performance to variations of the borehole length and shank spacing is investigated. The impact of the thermal interference between flowing legs, namely thermal short-circuiting, on parameters affecting the borehole thermal resistance is addressed. Furthermore, the energy exchange characteristics for different circuit configurations are quantified by introducing the thermal effectiveness coefficient. The results indicate that the borehole length is more influential than shank spacing in increasing the discrepancy between thermal performances of different circuit configurations. It is shown that deviation of the averaged-over-the-depth mean fluid temperature from the arithmetic mean of the inlet and outlet temperatures is more critical for lower shank spacings and higher borehole lengths. Full article

(This article belongs to the Special Issue Computational Geothermal Energy Applications)

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17 pages, 6046 KiB

Open AccessArticle

A Numerical Study on the Performance of Ground Heat Exchanger Buried in Fractured Rock Bodies

by Weisong Zhou, Peng Pei, Dingyi Hao and Chen Wang

Energies 2020, 13(7), 1647; https://doi.org/10.3390/en13071647 - 02 Apr 2020

Cited by 10 | Viewed by 2052

Abstract

The ground source heat pump (GSHP) is receiving increasing attention due to the global trend of energy-saving and emission reduction. However, projects with ground heat exchangers (GHEs) buried in fractured rock bodies are scarce, and the impacts of water flow in fractures on the system performance are short of detailed investigations. In this paper, a three-dimensional model was built to study the temperature distribution underground and the relative performance of heat pumps and GHEs influenced by groundwater flow in fractures. Three factors including fluid flow velocities in fractures, the number of fractures and the distributions of fractures were taken into consideration, a range of indicators including outlet temperature of GHEs, mean temperature of “Energy Storage Rock Body” (ESRB) and heat injection rate per unit length were examined. It was found that the heat injection rate per unit length of a U-pipe in fractured rock body could be up to 78.83% higher than that of a U-pipe in integrated rock. Likewise, the coefficient of performance of cases with fractures was identified to be up to 4.50% higher than the integrated rock case. In addition, differently distributed fractures also have different impacts on the heat transfer efficiency of heat pumps and GHEs. Full article

(This article belongs to the Special Issue Computational Geothermal Energy Applications)

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Review

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45 pages, 3149 KiB

Open AccessReview

Reviewing the Modeling Aspects and Practices of Shallow Geothermal Energy Systems

by Paul Christodoulides, Ana Vieira, Stanislav Lenart, João Maranha, Gregor Vidmar, Rumen Popov, Aleksandar Georgiev, Lazaros Aresti and Georgios Florides

Energies 2020, 13(16), 4273; https://doi.org/10.3390/en13164273 - 18 Aug 2020

Cited by 12 | Viewed by 4570

Abstract

Shallow geothermal energy systems (SGES) may take different forms and have recently taken considerable attention due to energy geo-structures (EGS) resulting from the integration of heat exchange elements in geotechnical structures. Still, there is a lack of systematic design guidelines of SGES. Hence, in order to contribute towards that direction, the current study aims at reviewing the available SGES modeling options along with their various aspects and practices. This is done by first presenting the main analytical and numerical models and methods related to the thermal behavior of SGES. Then, the most important supplementary factors affecting such modeling are discussed. These include: (i) the boundary conditions, in the form of temperature variation or heat flow, that majorly affect the predicted thermal behavior of SGES; (ii) the spatial dimensions that may be crucial when relaxing the infinite length assumption for short heat exchangers such as energy piles (EP); (iii) the determination of SGES parameters that may need employing specific techniques to overcome practical difficulties; (iv) a short-term vs. long-term analysis depending on the thermal storage characteristics of GHE of different sizes; (v) the influence of groundwater that can have a moderating effect on fluid temperatures in both heating and cooling modes. Subsequently, thermo-mechanical interactions modeling issues are addressed that may be crucial in EGS that exhibit a dual functioning of heat exchangers and structural elements. Finally, a quite lengthy overview of the main software tools related to thermal and thermo-hydro-mechanical analysis of SGES that may be useful for practical applications is given. A unified software package incorporating all related features of all SGES may be a future aim. Full article

(This article belongs to the Special Issue Computational Geothermal Energy Applications)

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