Feasibility of Coaxial Deep Borehole Heat Exchangers in Southern California

Feasibility of Coaxial Deep Borehole Heat Exchangers in Southern California | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Feasibility of Coaxial Deep Borehole Heat Exchangers in Southern California Haohua Chen, Ingrid Tomac This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4546850/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 01 Nov, 2024 Read the published version in Geothermal Energy → Version 1 posted 9 You are reading this latest preprint version Abstract This paper investigates the feasibility of Coaxial Deep Borehole Heat Exchanger (CDBHE) applications to the campus at the University of California San Diego (UCSD). By collecting different geophysical source data for various formations and well logs around the UCSD campus, a multilayered thermophysical model for the ground on the site is established. Circulation of water within a closed coaxial loop system considers the geothermal energy extraction under uncertainity consideration of the unknown deeper layers heat flow gradient as coupled with the variation of pipe insulation properties, flow rates, outer pipe diameter, grout and depths between 1 km and 4 km. A finite-element framework is constituted to model the Navier-Stokes fluid flow and heat transfer in the CDBHE system, and validated with a field test on CDBHE from the literature. It was found that a 4 km CDBHE could produce a thermal power of 600 kW under the optimum geological conditions at the UCSD site. Thermal power shares from different layers indicate that deeper formation layers contribute more to the thermal power than the shallower layers. An inner pipe with an insulated depth of 2 km produces only 1–6% less power than a fully insulated inner pipe for the 4 km CDBHE, and thus a partially insulated VIT-plastic inner pipe is suggested. Furthermore, the CDBHE thermal power increases by 5% when the grout thermal conductivity increases from 1 to 3.65 W/(K∙m), close to the formation thermal conductivity, and then maintains almost the same, and the 4 km CDBHE with flow rates of 2.78–6.94 L/s at the UCSD site can directly supply a low-temperature heating radiator system for room heating. The effects of the investigated factors provide guidelines for future geothermal resource exploitation in southern California. deep borehole heat exchanger renewable energy heat transfer geothermal Full Text Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 01 Nov, 2024 Read the published version in Geothermal Energy → Version 1 posted Editorial decision: Revision requested 14 Aug, 2024 Reviews received at journal 14 Aug, 2024 Reviewers agreed at journal 24 Jul, 2024 Reviews received at journal 17 Jul, 2024 Reviewers agreed at journal 27 Jun, 2024 Reviewers invited by journal 27 Jun, 2024 Editor assigned by journal 26 Jun, 2024 Submission checks completed at journal 26 Jun, 2024 First submitted to journal 07 Jun, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4546850","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":328674007,"identity":"d18fa5be-2d39-43cd-8ed5-1ba2208cc1b8","order_by":0,"name":"Haohua Chen","email":"","orcid":"","institution":"University of California San Diego","correspondingAuthor":false,"prefix":"","firstName":"Haohua","middleName":"","lastName":"Chen","suffix":""},{"id":328674008,"identity":"a7a66715-3ed1-4a9e-9470-1bc9ec6f1f61","order_by":1,"name":"Ingrid Tomac","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAqUlEQVRIiWNgGAWjYBACNghlAyIM4Fz8WiCK0kjQAlV0mAQtfPLNRzf8qDmf2N9/eAPDh7LDxDiMLe1mz7HbiTNupBUwzjhHlBYesxu8DbcTN0jwGDDzthGp5ebfhnOJG/jPGDD/JVbLbd6GA4kbGHIMmBmJ05KWdlvmWLIxyC8He86lE9Yi33z42M03NXaywBDb+OBHmTVhLSjgAInqR8EoGAWjYBTgAgCbEzka3AwobQAAAABJRU5ErkJggg==","orcid":"","institution":"University of California San Diego","correspondingAuthor":true,"prefix":"","firstName":"Ingrid","middleName":"","lastName":"Tomac","suffix":""}],"badges":[],"createdAt":"2024-06-07 14:56:56","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4546850/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4546850/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1186/s40517-024-00319-0","type":"published","date":"2024-11-01T16:12:57+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":68206494,"identity":"6b756644-24f6-4f0f-a8a0-d607693a2aa9","added_by":"auto","created_at":"2024-11-04 16:32:40","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":808065,"visible":true,"origin":"","legend":"","description":"","filename":"ChenTomacGEENR0.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4546850/v1_covered_a3051d11-40fa-4236-88a4-2832854bd6c1.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Feasibility of Coaxial Deep Borehole Heat Exchangers in Southern California","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"geothermal-energy","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"geen","sideBox":"Learn more about [Geothermal Energy](https://geothermal-energy-journal.springeropen.com/about)","snPcode":"40517","submissionUrl":"https://submission.springernature.com/new-submission/40517/3","title":"Geothermal Energy","twitterHandle":"@SpringerOpen","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"deep borehole heat exchanger, renewable energy, heat transfer, geothermal","lastPublishedDoi":"10.21203/rs.3.rs-4546850/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4546850/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis paper investigates the feasibility of Coaxial Deep Borehole Heat Exchanger (CDBHE) applications to the campus at the University of California San Diego (UCSD). By collecting different geophysical source data for various formations and well logs around the UCSD campus, a multilayered thermophysical model for the ground on the site is established. Circulation of water within a closed coaxial loop system considers the geothermal energy extraction under uncertainity consideration of the unknown deeper layers heat flow gradient as coupled with the variation of pipe insulation properties, flow rates, outer pipe diameter, grout and depths between 1 km and 4 km. A finite-element framework is constituted to model the Navier-Stokes fluid flow and heat transfer in the CDBHE system, and validated with a field test on CDBHE from the literature. It was found that a 4 km CDBHE could produce a thermal power of 600 kW under the optimum geological conditions at the UCSD site. Thermal power shares from different layers indicate that deeper formation layers contribute more to the thermal power than the shallower layers. An inner pipe with an insulated depth of 2 km produces only 1\u0026ndash;6% less power than a fully insulated inner pipe for the 4 km CDBHE, and thus a partially insulated VIT-plastic inner pipe is suggested. Furthermore, the CDBHE thermal power increases by 5% when the grout thermal conductivity increases from 1 to 3.65 W/(K∙m), close to the formation thermal conductivity, and then maintains almost the same, and the 4 km CDBHE with flow rates of 2.78\u0026ndash;6.94 L/s at the UCSD site can directly supply a low-temperature heating radiator system for room heating. 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