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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 (30 September 2021) | Viewed by 34173

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Prof. Dr. Javier F. Urchueguía

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Guest Editor

School of Industrial Engineering, Polytechnic University of Valencia, Camino de Vera s/n, 46022 Valencia, Spain
Interests: renewable heating and cooling; heat pumps; shallow geothermal energy; green house gas emission quantification systems; governance tools for GHG reduction
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The Guest Editor is delighted to invite you to submit contributions to a Special Issue of Energies on the subject area “Shallow Geothermal Energy 2020”. Shallow geothermal technology, often termed as ground source heat pumps (GSHP), is among the renewable heating and cooling technologies, one that offers a one-in-all approach to the urgent necessity of systems that are at the same time efficient, renewable, and highly integrable with other RES as well as within the existing electricity grid. In recent years, much research has been focused on critical areas to improve the cost, efficiency, and social acceptance of these systems, still finding serious barriers that hinder a more generalized adoption by different stakeholders. This Special Issue, thereafter, includes but is not necessarily limited to the following list of topics:

Open and hybrid systems and integration with other renewable energy sources;
Integration in the built environment;
Advances in design of systems;
Thermal response testing;
Improvement in materials;
Advances in drilling and installation methods;
Mapping of resources;
Social acceptance;
Life cycle cost analysis and other analytic methods.

Prof. Dr. Javier F. Urchueguía
Guest Editor

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
Ground source heat pumps
Thermal response testing
Hybrid system
Building integration
Drilling
Design software
Analytic or numeric heat transfer analysis
Life cycle analysis
Exergy analysis
Geothermal resource mapping
Open loop systems
Closed loop systems
Social acceptance
Material for pipes
Grouting
Phase change materials

Published Papers (11 papers)

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Research

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29 pages, 15037 KiB

Open AccessArticle

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

by Tomasz Sliwa, Patryk Leśniak, Aneta Sapińska-Śliwa and Marc A. Rosen

Energies 2022, 15(3), 1152; https://0-doi-org.brum.beds.ac.uk/10.3390/en15031152 - 04 Feb 2022

Cited by 4 | Viewed by 2022

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). Full article

(This article belongs to the Special Issue Shallow Geothermal Energy 2021)

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15 pages, 2298 KiB

Open AccessArticle

Ground-Source Heat Pump Systems: The Effects of Variable Trench Separations and Pipe Configurations in Horizontal Ground Heat Exchangers

by Yu Zhou, Asal Bidarmaghz, Nikolas Makasis and Guillermo Narsilio

Energies 2021, 14(13), 3919; https://0-doi-org.brum.beds.ac.uk/10.3390/en14133919 - 30 Jun 2021

Cited by 12 | Viewed by 2502

Abstract

Ground-source heat pump systems are renewable and highly efficient HVAC systems that utilise the ground to exchange heat via ground heat exchangers (GHEs). This study developed a detailed 3D finite element model for horizontal GHEs by using COMSOL Multiphysics and validated it against a fully instrumented system under the loading conditions of rural industries in NSW, Australia. First, the yearly performance evaluation of the horizontal straight GHEs showed an adequate initial design under the unique loads. This study then evaluated the effects of variable trench separations, GHE configurations, and effective thermal conductivity. Different trench separations that varied between 1.2 and 3.5 m were selected and analysed while considering three different horizontal loop configurations, i.e., the horizontal straight, slinky, and dense slinky loop configurations. These configurations had the same length of pipe in one trench, and the first two had the same trench length as well. The results revealed that when the trench separation became smaller, there was a minor increasing trend (0.5 °C) in the carrier fluid temperature. As for the configuration, the dense slinky loop showed an average that was 1.5 °C lower than those of the horizontal straight and slinky loop (which were about the same). This indicates that, when land is limited, compromises on the trench separation should be made first in lieu of changes in the loop configuration. Lastly, the results showed that although the effective thermal conductivity had an impact on the carrier fluid temperature, this impact was much lower compared to that for the GHE configurations and trench separations. Full article

(This article belongs to the Special Issue Shallow Geothermal Energy 2021)

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26 pages, 9828 KiB

Open AccessArticle

Impact of Employing Hybrid Nanofluids as Heat Carrier Fluid on the Thermal Performance of a Borehole Heat Exchanger

by Hossein Javadi, Javier F. Urchueguia, Seyed Soheil Mousavi Ajarostaghi and Borja Badenes

Energies 2021, 14(10), 2892; https://0-doi-org.brum.beds.ac.uk/10.3390/en14102892 - 17 May 2021

Cited by 19 | Viewed by 2321

Abstract

In this numerical study, 4 types of hybrid nanofluid, including Ag-MgO/water, TiO₂-Cu/water, Al₂O₃-CuO/water, and Fe₃O₄-multi-wall carbon nanotube/water, have been considered potential working fluid in a single U-tube borehole heat exchanger. The selected hybrid nanofluid is then analyzed by changing the volume fraction and the Reynolds number. Based on the numerical results, Ag-MgO/water hybrid nanofluid is chosen as the most favorable heat carrier fluid, among others, considering its superior effectiveness, minor pressure drop, and appropriate thermal resistance compared to the pure water. Moreover, it was indicated that all cases of Ag-MgO/water hybrid nanofluid at various volume fractions (from 0.05 to 0.20) and Reynolds numbers (from 3200 to 6200) could achieve better effectiveness and lower thermal resistances, but higher pressure drops compared to the corresponding cases of pure water. Nevertheless, all the evaluated hybrid nanofluids present lower coefficient of performance (COP)-improvement than unity which means that applying them as working fluid is not economically viable because of having higher pressure drop than the heat transfer enhancement. Full article

(This article belongs to the Special Issue Shallow Geothermal Energy 2021)

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17 pages, 23493 KiB

Open AccessFeature PaperArticle

A Case Study of Thermal Evolution in the Vicinity of Geothermal Probes Following a Distributed TRT Method

by Hans Schwarz, Borja Badenes, Jan Wagner, José Manuel Cuevas, Javier Urchueguía and David Bertermann

Energies 2021, 14(9), 2632; https://0-doi-org.brum.beds.ac.uk/10.3390/en14092632 - 04 May 2021

Cited by 4 | Viewed by 1929

Abstract

To meet the stated climate change targets and to ensure the capability of meeting the current and future energy demands, there is an urgent need to develop renewable energy sources, such as geothermal systems. If geothermal systems are to be cost-efficient and are to enjoy public confidence, it is essential that they are designed and installed in accordance with the prevailing site-specific conditions. A thorough understanding of the thermal behaviour of the surrounding ground is, therefore, critical. In this work, we investigated temperature and its evolution in the vicinity of a shallow geothermal helix-shaped borehole heat exchanger (BHE). To measure the temperature close to the actual geothermal system, an additional U-tube probe was installed at the edge of the same borehole. A thermal load was then applied to the BHE, and the temperature was detected in the nearby U-tube. The temperature measurements were made with a GEOSniff monitoring device. To understand these localised temperature measurements in the context of the Valencia test site, ERT measurements were also performed. The GEOSniff device permits measurements to be made with very high depth resolution, which allows the thermal properties of the surrounding ground to be derived precisely, thus, enabling the identification of the different textural domains. Full article

(This article belongs to the Special Issue Shallow Geothermal Energy 2021)

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12 pages, 1605 KiB

Open AccessArticle

Evaluation of the Effect of Anti-Corrosion Coatings on the Thermal Resistance of Ground Heat Exchangers for Shallow Geothermal Applications

by Gianluca Cadelano, Alessandro Bortolin, Giovanni Ferrarini, Paolo Bison, Giorgia Dalla Santa, Eloisa Di Sipio, Adriana Bernardi and Antonio Galgaro

Energies 2021, 14(9), 2586; https://0-doi-org.brum.beds.ac.uk/10.3390/en14092586 - 30 Apr 2021

Cited by 6 | Viewed by 1904

Abstract

The materials and the technology used to build the ground heat exchangers significantly affect the heat transfer performance of a geothermal system, in addition to the local geological and hydrogeological context. Among expense items such as the coupled heat pumps and the applied drilling technology, the heat exchangers play a key role in the shallow geothermal market. For this reason, they are usually made with plastic. Metal tubes are not widely used because of corrosion issues, which can compromise the reliability of the system over time. According to best practices, metal is an unfavorable choice if the pipes are not made of corrosion resistant alloys, such as stainless steel, but the overall performance is strongly related to the heat transfer efficiency. In this study, laser-flash technique is applied on carbon steel samples with anti-corrosion coatings and on corrosion resistant materials (stainless steel grades used for pipes), thus, allowing the comparison of their thermophysical properties. These properties are used to evaluate each solution in terms of thermal resistance. This study demonstrates that there are no particular corrosion resistant steel pipe configurations that are thermally favorable over others in a critical way. Full article

(This article belongs to the Special Issue Shallow Geothermal Energy 2021)

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30 pages, 13886 KiB

Open AccessArticle

Numerical Study on the Thermal Performance of a Single U-Tube Borehole Heat Exchanger Using Nano-Enhanced Phase Change Materials

by Hossein Javadi, Javier F. Urchueguia, Seyed Soheil Mousavi Ajarostaghi and Borja Badenes

Energies 2020, 13(19), 5156; https://0-doi-org.brum.beds.ac.uk/10.3390/en13195156 - 03 Oct 2020

Cited by 38 | Viewed by 2956

Abstract

To investigate the impacts of using nano-enhanced phase change materials on the thermal performance of a borehole heat exchanger in the summer season, a three-dimensional numerical model of a borehole heat exchanger is created in the present work. Seven nanoparticles including Cu, CuO, Al₂O₃, TiO₂, SiO₂, multi-wall carbon nanotube, and graphene are added to the Paraffin. Considering the highest melting rate and lowest outlet temperature, the selected nano-enhanced phase change material is evaluated in terms of volume fraction (0.05, 0.10, 0.15, 0.20) and then the shape (sphere, brick, cylinder, platelet, blade) of its nanoparticles. Based on the results, the Paraffin containing Cu and SiO₂ nanoparticles are found to be the best and worst ones in thermal performance improvement, respectively. Moreover, it is indicated that the increase in the volume fraction of Cu nanoparticles could enhance markedly the melting rate, being 0.20 the most favorable value which increased up to 55% the thermal conductivity of the nano-enhanced phase change material compared to the pure phase change material. Furthermore, the blade shape is by far the most appropriate shape of the Cu nanoparticles by considering about 85% melting of the nano-enhanced phase change material. Full article

(This article belongs to the Special Issue Shallow Geothermal Energy 2021)

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29 pages, 8535 KiB

Open AccessArticle

Theoretical and Experimental Cost–Benefit Assessment of Borehole Heat Exchangers (BHEs) According to Working Fluid Flow Rate

by Borja Badenes, Miguel Ángel Mateo Pla, Teresa Magraner, Javier Soriano and Javier F. Urchueguía

Energies 2020, 13(18), 4925; https://0-doi-org.brum.beds.ac.uk/10.3390/en13184925 - 19 Sep 2020

Cited by 14 | Viewed by 2443

Abstract

In ground-source heat-pump systems, the heat exchange rate is influenced by various design and operational parameters that condition the thermal performance of the heat pump and the running costs during exploitation. One less-studied area is the relationship between the pumping costs in a given system and the heat exchange rate. This work analyzes the investment and operating costs of representative borehole heat-exchanger configurations with varying circulating flow rate by means of a combination of analytical formulas and case study simulations to allow a precise quantification of the capital and operational costs in typical scenario. As a conclusion, an optimal flow rate minimizing either of both costs can be determined. Furthermore, it is concluded that in terms of operating costs, there is an operational pumping rate above which performance of geothermal systems is energetically strongly penalized. Full article

(This article belongs to the Special Issue Shallow Geothermal Energy 2021)

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15 pages, 5605 KiB

Open AccessArticle

Evaluation of Suitable Areas to Introduce a Closed-Loop Ground Source Heat Pump System in the Case of a Standard Japanese Detached Residence

by Gaurav Shrestha, Mayumi Yoshioka, Hikari Fujii and Youhei Uchida

Energies 2020, 13(17), 4294; https://0-doi-org.brum.beds.ac.uk/10.3390/en13174294 - 19 Aug 2020

Cited by 4 | Viewed by 1943

Abstract

Evaluation of appropriate areas to introduce a closed-loop ground-source heat pump (GSHP) system in the case of a standard detached residence was conducted in Akita Plain, Japan. Depth of borehole heat exchanger (BHE) required to use a GSHP system was taken as the suitability index, which is simpler for the general public to understand and to promote the system. Heating and cooling loads of the standard size detached residence were calculated based on the 2013 Energy Conservation Standard. To estimate BHE depths and estimate a suitable area, identical 3D BHE models were constructed at 30 points in the plain. Required BHE depths were determined by performing heat exchange simulations at each location using the calculated loads and heat exchange rates. A suitability map showing distribution of the required BHE depths was prepared. BHE depths were shorter in the north-western area compared to the other parts, implying that the coastal lowlands in this area are more suitable for closed-loop system in the standard detached residences in terms of heat exchange performance as well as the cost reduction. Thickly distributed Quaternary System with higher thermal conductivity is contributing to shorter BHE depths. The suitability map is effective to adopt potential areas for the system installation in the standard detached Japanese residences. Full article

(This article belongs to the Special Issue Shallow Geothermal Energy 2021)

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15 pages, 2760 KiB

Open AccessArticle

Synergistic Effect of Expanded Graphite-Silane Functionalized Silica as a Hybrid Additive in Improving the Thermal Conductivity of Cementitious Grouts with Controllable Water Uptake

by Ilayda Berktas, Ali Nejad Ghafar, Patrick Fontana, Ayten Caputcu, Yusuf Menceloglu and Burcu Saner Okan

Energies 2020, 13(14), 3561; https://0-doi-org.brum.beds.ac.uk/10.3390/en13143561 - 10 Jul 2020

Cited by 8 | Viewed by 2614

Abstract

Recently, a growing demand for geothermal applications has led to the exploitation of energy efficiently by developing grouting materials in the borehole between pipes and the ground. Therefore, the current study developed newly formulated cementitious grouts by the integration of expanded graphite (EG)-based hybrid additives synthesized by building chemical bridges between silica particles and EG in the presence of amino functional silane coupling agents. These produced hybrid additives with controlled EG and silica ratios were utilized in grout mixtures used in borehole heat exchangers to enhance the thermal conductivity. According to the optimization study on the formulation development of grout mixtures with bentonite, silica sands, cement, and superplasticizer by adding neat EG and EG-based hybrids, the relationship between the carbon amount and water demand was found to have a significant impact on thermal conductivity. The highest thermal conductivity value of 2.656 W/mK was achieved by the incorporation of 5 wt% hybrid additive with the ratio silica/EG of 1:5 compared to the reference grout, which showed a thermal conductivity of 2.373 W/mK. Therefore, the enhancement in thermal conductivity was dependent on the increase in the EG content and also the additive loading ratio, resulting in a slight increase in the water demand. Full article

(This article belongs to the Special Issue Shallow Geothermal Energy 2021)

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Review

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15 pages, 3177 KiB

Open AccessReview

Heat Transfer and Bearing Characteristics of Energy Piles: Review

by Jinli Xie and Yinghong Qin

Energies 2021, 14(20), 6483; https://0-doi-org.brum.beds.ac.uk/10.3390/en14206483 - 10 Oct 2021

Cited by 7 | Viewed by 2714

Abstract

Energy piles, combined ground source heat pumps (GSHP) with the traditional pile foundation, have the advantages of high heat transfer efficiency, less space occupation and low cost. This paper summarizes the latest research on the heat transfer and bearing capacity of energy piles. It is found that S-shaped tubes have the largest heat transfer area and the best heat transfer efficiency; that energy piles need to be designed conservatively, such as adjusting the safety coefficient, number and spacing of the piles according to the additional temperature loads; and that unbalanced surface temperature has not been resolved, caused by uneven refrigeration/heating demand in one cycle. A composite energy pile applied to water-rich areas is proposed to overcome the decay of bearing and heat transfer performance. Besides, most of the heat transfer models are borehole-oriented and will fit for energy piles effectively if the models support variable ground temperature boundary conditions. Full article

(This article belongs to the Special Issue Shallow Geothermal Energy 2021)

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33 pages, 7289 KiB

Open AccessReview

A Review of the Performance of Minewater Heating and Cooling Systems

by David B. Walls, David Banks, Adrian J. Boyce and Neil M. Burnside

Energies 2021, 14(19), 6215; https://0-doi-org.brum.beds.ac.uk/10.3390/en14196215 - 29 Sep 2021

Cited by 17 | Viewed by 9082

Abstract

As the decarbonisation of heating and cooling becomes a matter of critical importance, it has been shown that flooded mines can provide a reliable source of low-carbon thermal energy production and storage when coupled with appropriate demand via an appropriate heat transfer technology. This paper summarises the potential resource represented by a long legacy of mining operations, the means heat can be extracted from (or rejected to) flooded mine workings, and then considers the risks and challenges faced by minewater geothermal energy (MWG) schemes in the planning, construction, and operational phases. A combination of site visits, interviews and literature reviews has informed concise, updated accounts for many of the minewater geothermal energy systems installed across the world, including accounts of hitherto unpublished systems. The paper has found that a number of previously reported MWG schemes are now non-operational. Key risks encountered by MWG schemes (which in some cases have led to decommissioning) include clogging of system components with mineral precipitates (e.g., ochre), uncertainty in targeting open mine voids and their hydraulic behaviour, uncertainty regarding longevity of access to minewater resource, and accumulated ongoing monitoring and maintenance burdens. Full article

(This article belongs to the Special Issue Shallow Geothermal Energy 2021)

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