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COPYRIGHT © 2016 TAYLOR and FRANCIS GROUP, LONDON, UK CRC PRESS / BALKEMA - PROCEEDINGS AND MONOGRAPHS IN ENGINEERING, WATER AND EARTH SCIENCES WWW.CRCPRESS.COM, WWW.TAYLORANDFRANCIS.COM ISBN 978-1-138-03299-6 Energy Geotechnics Editors: Frank Wuttke, Sebastian Bauer and Marcelo Sánchez help open EnergyGeotechnics–Wuttke,Bauer&Sánchez(Eds) ©2016Taylor&FrancisGroup,London,ISBN978-1-138-03299-6 Committees INTERNATIONALADVISORYBOARD TonyAmis(UK) FernandoPardo(Spain) MalekBouazza(Australia) Jean-MichelPereira(France) LeonardoCabral(Brazil) EnriqueRomero(Spain) Gye-ChunCho(Korea) MarceloSánchez(US) Yu-JunCui(France-China) TomSchanz(Germany) PierreDelage(France) KenichiSoga(UK) AntonioGens(Spain) J.CarlosSantamarina(US) LeonardoGuimaraes(Brazil) AnhMinhTang(France) JaccoHaasnoot(Netherlands) HywelThomas(UK) TomaszHueckel(US) IvanVerdugo(Colombia) LyesseLaloui(Switzerland) ThomasVienken(Germany) M.R.Lakshmikantha(Spain) PeterBourne-Webb(Portugal) JohnMcCartney(US) FrankWuttke(Germany) GuillermoNarsilio(Australia) TaeSupYun(Korea) DuncanNicholson(UK) DietmarAdam(Austria) GuneyOlgun(US) NATIONALTECHNICALPROGRAMCOMMITTEE FrankWuttke,KielUniversity,Germany SebastianBauer,KielUniversity,Germany AndreasDahmke,KielUniversity,Germany TomSchanz,RUBochum,Germany RolfKatzenbach,TUDarmstadt,Germany ErnstHuenges,GFZPotsdam,Germany OlafKolditz,UFZLeipzig,Germany StavrosSavidis,TUBerlin,Germany DietmarAdam,TUWien,Austria MINISYMPOSIAORGANIZERS Dietmar Adam (TU Wien, Austria) and Malek Bouazza (Monash University, Australia) – Minisymposium thermo-activefoundations,tunnelsandearth-coupledstructures Marcelo Sánchez (Texas A & M University, USA) and Christian Deusner (GEOMAR, Germany) – Minisymposiumgeomechanicalcharacterizationandmodelingofhydratebearingsediments DavidM.J.Smeulders(EindhovenUniversityofTechnology,TheNetherlands)andSebastianBauer&Frank Wuttke (Kiel University, Germany) – Minisymposium trends and challenges in energy geotechnical storage systemsandmaterials RobertCharlier(UniversitédeLiège,Belgium)andBertrandFrançois(UniversitéLibredeBruxelles,Belgium)– Minisymposiumshallowgeothermalsystems Pierre Duffaut (French Committee on Rock Mechanics) – Minisymposium geotechnics risk and items for undergroundnuclearpowerplants Enrique Romero (Universitat Politècnica de Catalunya UPC, Spain), Xiangling Li (European Underground Research Infrastructure for Disposal of Nuclear Waste In Clay Environment EIG EURIDICE, Belgium) andPaulMarschall(NationaleGenossenschaftfürdieLagerungRadioaktiverAbfälleNAGRA,Switzerland)– Minisymposiumgeotechnicsfornuclearwastedisposal XIII CONFERENCEORGANIZATIONANDTECHNICALENQUIRIES HenokHailemariam,HemMotraandFrankWuttke GeomechanicsandGeotechnics KielUniversity,Germany LISTOFREVIEWERS MalekBouazza EnriqueRomero DietmarAdam PierreDuffaut ChristianDeusner PaulMarschall MarceloSánchez XianglingLi SebastianBauer HenokHailemariam FrankWuttke ZarghaamH.Rizvi RobertCharlier DineshShrestha BertrandFrançois AmirS.Sattari DavidM.J.Smeulders XIV EnergyGeotechnics–Wuttke,Bauer&Sánchez(Eds) ©2016Taylor&FrancisGroup,London,ISBN978-1-138-03299-6 Preface The1stInternationalConferenceonEnergyGeotechnics(ICEGT2016)washeldfrom29thto31stAugust2016, attheUniversityofKiel,Kiel,Germany.ThiswasthefirstconferenceundertheguidanceoftheInternational SocietyforSoilMechanicsandGeotechnicalEngineering(ISSMGE)TC308onEnergyGeotechnics. Withtheincreasingenergydemandandclimatechangeimplications,thedevelopmentofsustainableenergy systemsbasedonintegratedschemesofenergyproduction,transport,andtransferaswellasenergystorageis oftheutmostimportance.Thisissueisofincreasinginteresttotheresearchfieldofgeotechnicalengineering. Thefocusofthisrelativelynewresearchareaisnewdevelopmentsandsolutionsforcivil,environmental,and industrialapplications. Thebehaviourofgeomaterials(i.e.soilsandrocks)whensubjectedtothermo-hydro-mechanicalandchemical solicitationsisgenerallyverycomplex.Theirresponseisalsostronglyinfluencedby,shape,sizeandmineralogy oftheaggregates,aswellas,bythetypeofloadingandporosity.Theabilityofthesematerialstostoreand dissipateenergyisofgreatimportancetoenergytransportationandstoragesystems.Besidetheunderstanding ofthematerialbehaviour,thestudyanddevelopmentofenergygeo-structureaswellthemultiphysicsinteraction behaviourbecomesofhighestimportancetoo. Theaimoftheconferencewastoprovideawideplatformfortheinteractionamongcolleaguesfromdifferent countriesworkingindifferentsubjects,andplayingdifferentrolesintheenergysector.Thediscussionsfocusedon past,presentandfutureinvestigations&practicesintheareaofenergygeotechnics,coveringfromexperimental uptonumericalandfundamentalstudies. This proceedings consists of 97 peer reviewed papers from engineers and researchers, investigations and reportingfromtheirfindings.Theeditorswishthatthisproceedingsactsasastackofknowledgeforthefrontier ofEnergyGeotechnics. FrankWuttke ChairmanoftheICEGT2016 HeadofGeomechanicsandGeotechnics KielUniversity XI EnergyGeotechnics–Wuttke,Bauer&Sánchez(Eds) ©2016Taylor&FrancisGroup,London,ISBN978-1-138-03299-6 Sponsors ORGANIZINGINSTITUTION KielUniversity,Germany ORGANIZINGASSOCIATION ISSMGETC308onEnergyGeotechnics SPONSORS FugroConsultGmbH,Germany (Platin-Sponsor) APSAntriebs-,Prüf-undSteuertechnik GmbH,Germany(Gold-Sponsor) SUPPORTINGAUTHORITIES BusinessDevelopmentandTechnology TransferCorporationofSchleswig- Holstein,Germany XVII EnergyGeotechnics–Wuttke,Bauer&Sánchez(Eds) ©2016Taylor&FrancisGroup,London,ISBN978-1-138-03299-6 Acknowledgements WewouldliketothankGEOMARHelmholtzCentreforOceanResearch(Kiel,Germany),AndreLindhorst (Pur.pur, Kiel, Germany), Dietmar Adam (TU Wien, Austria) and Stiftung OFFSHORE-WINDENERGIE (Berlin, Germany) for providing us with the photos used on the conference webpage as well as on the front bookcover. We would also like to thank Henok Hailemariam (Kiel University, Kiel, Germany) for his outstanding organizationalworkintheICEGT2016. XV EnergyGeotechnics–Wuttke,Bauer&Sánchez(Eds) ©2016Taylor&FrancisGroup,London,ISBN978-1-138-03299-6 Potential of district-scale geothermal energy in urban cities K.Soga,Y.Zhang&R.Choudhary UniversityofCambridge,Cambridge,UK ABSTRACT: Groundsourceheatpumps(GSHPs)isashallowgeothermalsystemofpumpingheatfromor tothegroundtosupplylowcarbonheatingorcoolingtobuildings.Theundergroundbecomesaheartstorage andcombinationofheatingandcoolingcanbebeneficialtosystemefficiencyimprovementandtemperature balanceunderground.Inthisstudy,aGISbasedsimulationtoolwasdevelopedtoquantifyhowmanyGSHPs couldbeinstalledatadistrictoracityscalewithoutlosingcontrolofgroundthermalcapacity,andtoidentifyits contributiontobothheatingandcoolingdemandsofbuildings.TheCityofWestminster,Londonwasselected asacasestudy.Resultsshowthatmanybuildings(morethan50%)caninstallenoughboreholestosupporttheir ownheatingandcoolingdemands.Forhigh-risebuildingsandthehighpeopledensityinfrastructures,thelimited spaceforgeothermalenergyextractionisaconcernforgeothermalapplications.Asdomesticbuildingshave morespacetoinstallboreholesandthustoobtainmoreenergyfromunderground,residentialhousescanshare theirsurplusgeothermalenergywithcommercialbuildingsandurbaninfrastructureatcityscale.Parametric analysiswascarriedouttoinvestigatetheinfluenceofdistrictsizeforsharingaGSHPnetworkatcityscale. 1 INTRODUCTION utilisetheheatconvectionmechanismofgroundwa- terflowbyextractingheatedorcooledwater.Vertical IntheUK,£32billionisspentonheatingeveryyear GSHPsarenormallyconstructedbyplacingtwosmall- andtheheatconsumptionaccountsforapproximatelya diameter polyethylene tubes in a vertical borehole thirdoftotalgreenhousegasemissions.Asspaceheat- (typically150mdeep),whichhorizontalGSHPsare ing accounts for about 66% of the domestic energy placed in narrow trenches and this design requires bills (DECC, 2013a) and delivers approximate 74% greateramountofgroundarea.TheverticalGSHPsare ofthecarbondioxideemissions,themajorityofheat commonlychosenforurbanareasbecausetheyneed relatedactivitiesarefromfossilfuelconsumptionin relatively small plots of space; contact with the soil the domestic sector (DECC, 2012). Many countries thatvarieslittleintemperatureandthermalproperties; whichhavesimilarsituationencouragetheadaptation consume the smallest amount of pipe and pumping ofrenewableenergytechnologies.Aspartof2009EU- energy;andcanyieldthemostefficientperformance. wideactiontoincreasetheuseofrenewableenergy, Fortheexistingbuildingsinurbanareas,closedver- theUKgovernmenthascommittedtoset15%renew- ticalloopsareusedduetospacelimitationsandtheir ableenergytargetby2020.Thisisasignificantrise systemefficiency. comparedwithapproximate2%in2008. Additional requirement for heat network is bet- Itistraditionallyconsideredthatheatisgenerated tertoprovidecoolingaswell.Coolingisplayingan on-site in individual buildings and the most com- increasing part in comfort satisfactory in buildings, monsourcesareelectricheaters,gasboilers,andoil especiallyintheofficesandothercommercialbuild- boilers.Groundsourceheatpumps(GSHPs)isashal- ings.Thecoolingdemandisprojectedtogrowfurther. low geothermal system of pumping heat from or to The combination of heating and cooling can make the ground to supply low carbon heating or cool- district energy more economically attractive in the ingtobuildings.Shallowgeothermalsystemsrequire areaswithamixoflandusebuildings(DECC,2012; nospecificgeologicalconditionorhightemperature DECC, 2013a). GSHP systems can match with this gradient,sotheyareincreasinglypopularworldwide requirement.Notonlyiscoolingsupplyabasicfunc- asanenvironmentalfriendlyalternativetotraditional tionfortheGSHPsystem,butcombinationofheating technologies such as gas fired boilers (Haehnlein and cooling can be also greatly beneficial to sys- etal.,2010). temefficiencyimprovementandtemperaturebalance GSHPs can be mainly grouped into two types, underground.Theundergroundessentiallybecomesa closedloopsandopenloops.InclosedGSHP,borehole heartstorage. system achieves heat exchange through the circula- The benefits of GSHP systems also include low tionoffluidinaclosedU-loopembeddedwithinan runningcost,minimalmaintenancecostandlonglife infillmedium.Incontrast,openloopGSHPsystems expectancy. Heat pump can be expected to use for 3 20–25 years and the borehole can be used as long peakandanofficebuildingwithday-timepeaks,so as100years(KensaHeatPumps,2014).Inorderto thattheheatingloadcanbeallowedtogetbalanced. encourage the growth of this technology in the UK, AccordingtotheheatstrategyoftheUKgovernment, RenewableHeatIncentive(RHI)classifiedtheGSHP providedtheycanbeusedtodistrictheatfromlowcar- district heating into non-domestic tariff stream.The bonsources,heatnetworkscanbethecoreandhave systemiseligibletoreceive8.7penceperkWhheating greatpotentialtoplayakeyroleinachievingtargeted consumptionforaslongas20years(DECC,2013c). lowcarbonheatsupplyby2050(DECC,2012). AlthoughGSHPhasbeenavailableforlongtime, Although district heating has started since the theirapplicationsaregenerallylimitedtoasmallscale. 1950’s, the market penetration is still quite low.The If such ground source energy systems are employed typicaldistrictheatingareuniversitycampuses,new atalargerscaletoprovidelowcarbonheatingsolu- innercitycommercialbuildingsandurbaninfrastruc- tions to buildings and infrastructures, a low carbon tures (DECC, 2013b). It is estimated that networks citywouldbedeveloped.AccordingtotheUKEnvi- currently provide less than 2% of UK heat demand, ronmentAgency(2009),thetotalnumberofinstalled including 1600 networks (DECC, 2013b) serving GSHP systems in the UK at the time of year 2009 around210,000dwellingsand1700commercialand was8000,ofwhich,therewereonly300openloops publicbuildingsacrosstheUK(TheAssociationfor (3.75%)andtherestareclosedloops(96.75%).There DecentralisedEnergy,2015).Thispercentageismuch has only a very few works on evaluating the poten- lower than the average value of 10% in Europe. In tialcapacityandsustainabilityofshallowgeothermal someotherpartsofEurope,thedistrictheatingappli- energyatalargescale. cationsaremuchwiderspread.InDenmark,Finland Inthisstudy,aGISbasedsimulationtoolwasdevel- andSweden,forexample,themarketsharesarehigh oped to quantify the number of GSHPs that can be toaround70%,49%and50%,respectively(DECC, installed at a district or a city scale without losing 2012). In some countries, although the district heat- controlofgroundthermalcapacity,andtoidentifyits ing contributes a low percentage at the nation scale, contributiontobothheatingandcoolingdemandsof it makes a major supply in large cities. For exam- buildings.PreviouslyZhangetal.(2014;2015)used ple, district heating provides only 18% of total heat thismodeltothecityofWestminster,London.Results inAustria, but the percentage is doubled to be 36% showthatmorethan50%ofthebuildingscaninstall forVienna(Poyry,2009).Thepotentialestimatedby enough boreholes to support their own heating and DECC is to supply 14% of all homes in the UK by cooling demands. Although such large scale GSHP 2050(DECC,2012). installationscanapproachlong-termheatingcostsav- There are currently many types of heat sources ing of up to 70% (Committee on Climate Change, available. However, in order to achieve the Carbon 2013),itstillrequiresmorethan20yearsforageneral Plan by 2050, low carbon intensive ways over long domestichometogetfullcost-recovery.Hencemore termarerequiredbythegovernmenttoheatthebuild- proactiveefforttoincreasetheadoptionrateofGSHP ings relying on coal, oil, and even the natural gas isrequiredfrombothcommercialandregulatorysides. (HMGovernment,2011).Inaddition,DECChavealso A small scale district heating/cooling system is givenfurthersupporttoheatnetworksintheRenew- an attractive solution to implement the low carbon ableHeatIncentivePolicy(DECC,2013c).Moreover, energyutilization.Forhigh-risebuildingsandthehigh EnergyCompanyObligation(ECO),asubsidyfrom people density infrastructures, the limited space for energy suppliers, works alongside the Green Deal geothermalenergyextractionisaconcernforgeother- toprovideenergy-savingimprovementforvulnerable mal applications. As domestic buildings have more households.Thedistrictheatinghasbeenconsidered space to install boreholes and thus to obtain more as a primary measure (DECC, 2015).The Office of energyfromunderground,residentialhousescanshare Gas and Electricity Markets (Ofgem) has recently their surplus geothermal energy with commercial confirmedthelifetimeofGSHPdistrictheatingcon- buildingsandurbaninfrastructureatcityscale.This nectionsare40yearsunderECO(DECC,2014). paperextendstheworkoftheauthors(Zhangetal., Unlikethesinglesystem,theheatpumpusedinthe 2014;2015)byconsideringthepotentialofashallow districtsystemcanbeeitheracentralisedsystemwitha geothermaltechnologyfordistrictscaleheating. largerheatpumporade-centralisedsystemwithmul- tiplesofsmallercontrolledheatpumps(DECC,2012). Inbothofcases,theheatpumpsshouldbeconnectedto 2 DISTRICTSCALEHEATINGANDCOOLING acommunalgroundarrayincludingoneormorebore- hole heat exchangers (BHE) to collect energy from Adistrictheatingnetworkiseithertwoormoredis- ground. In the design process of BHE, the coverage tinctbuildingsconnectedtoasingleheatsourceoron ofthetargetedareathatreceivesenergysupplyshould buildinginwhichtherearemorethantenindividual be firstly confirmed.The next step is to investigate customersconnectedtoasingleheatsource(DECC, all the geological site information and the building 2013b). Heat networks are to transport heat to con- load information for design.With all these prepared sumersthroughanetworkofinsulatedpipes.Theyare work,thetotalrequiredboreholelengthcanbefinally abletodeliverheattotheareaswithamixofsources calculated.AfterdeterminingthetotalrequiredBHE ofdemandsuchasaresidentialhousewithnight-time length,themostimportanttaskbeforeinstallationis 4 toconsideraboreholearrayforthereasonabledistrict is the building design heating block load (W), q is lc sharing.Thearrayarrangementwilldecidewhatisthe thebuildingdesigncoolingblockload(W),R isthe ga proportionofthetotalrequiredlengthcanbesatisfied. effective thermal resistance of the ground in annual Therefore,theboreholearrayandthesizeofthetar- pulse(mK/W),R istheeffectivethermalresistance gd geteddistrictarethetwokeyparameterstoinfluence ofthegroundindailypulse(mK/W),R istheeffec- gm thecapacityofaGSHPdistrictsystem. tivethermalresistanceofthegroundinmonthlypulse (mK/W), R is the thermal resistance of borehole b (mK/W), t is the undisturbed ground temperature g 3 CITY-SCALEGSHPSIMULATOR (K),tp isthetemperaturepenaltyforinterferenceof adjacent boreholes (K), t is the liquid temperature wi 3.1 Background at heat pump inlet (K), two is the liquid temperature at heat pump outlet (K), W is the power input at The efficiency of a vertical GSHP system is highly h design heating load (W), and W is the power input dependent on correctly sizing the ground heat c atdesigncoolingload(W). exchangers according to energy demand (Shonder TheGIStoolgivestheoutputofthetotalrequired andHughes,1998).Inordertoestimatethenumbers borehole length of GHE per building, which is the of GSHPs that can be installed in specific areas of largeroneoftheresultsfromEquations(1)and(2).The cities or districts, and the numbers that are required individual borehole length is set typically as 150m, tosatisfyheatingdemands,itisnecessarytoquantify whichisthecommon-usedvalueinpracticeforverti- the geothermal capacity using high-resolution infor- cal closed loop GSHP installations. The number of mation about land-use, underground conditions and boreholes per building is then calculated based on heating/coolingdemand. thesetwolengthvalues. Zhangetal.(2014;2015)developedasimulation Thelandareamaynotbeenoughfortherequired tool that integrates, within a geographic informa- numberofboreholesforsomebuildings.Insuchcases, tionsystem(GIS),high-resolutionlandusedatasets, themaximumpossibleboreholelength(themaximum heating/cooling demands of buildings, ground prop- boreholenumber×150m)foralandareaisprovided erties,andthegroundheatexchanger(GHE)design as input into the model.The model inversely calcu- calculations.APYTHONcodethatestimatesthesize latesthemaximumheatingandcoolingdemandsthat of GSHP required for a given heat demand of a can be provided by a GSHP system for that build- building was developed and embedded intoArcGIS ing.Inthisstudy,theGSHPcapacityofabuildingis software,whichisawidelyusedplatformforspatial definedastheratioofcapacitytodemand(C/D),and design and analysis. This integrated simulation tool calculated by dividing the maximum possible num- hasbeenusedtoquantifytheexactgeothermalcapac- berofboreholeswithinthebuilding’slandareabythe ity of specific areas.A brief overview of the tool is requiredboreholenumber.IftheC/Dratioofabuild- giveninthissection,butfurtherdetailscanbefound ingisequaltoorgreaterthan100%,bothheatingand inZhangetal.(2014;2015). coolingdemandsofthisbuildingcouldbesatisfiedby MostcurrentGHEdesignsoftwarepackagesrefer itsownGSHPsystem. to the Cylinder and Line Source Method, which has been found to be the most accurate model through comparisons with calibrated data from actual instal- 3.2 CaseStudy:ThecityofWestminster,London lations(ShonderandHughes,1998).Thetoolutilises The influence of switching the single system to the the following heat transfer equation that determines district network system on the GSHP satisfactory the required vertical borehole length L for heating h capacityatthecityscalewasinvestigatedforthecity (KavanaughandRafferty,1997). ofWestminster, London.The site specific or spatial inputsinthedesigncalculationwerefirstlyprepared for the case study, which were heating demand per building,coolingdemandperbuilding,thermalcon- ductivity,thermaldiffusivity,andgroundtemperature. Inadditiontothespatialdata,relatedconditionsand assumptionsfortheGSHPandtheboreholearelisted TherequiredverticalboreholelengthLcforcoolingis inTable1. foundusingthefollowingequation. Forthecalculationofheatingandcoolingdemands, UKMap, a GIS database, was used to obtain spatial informationaboutbuildingswithintheCityofWest- minsterincludingbuildingtype,floorareaandheight. According to this database (see Figure 1), there are 95,817buildingswithinthisdistrict.83%ofthefloor area is made up of residences, offices, and retail. whereF istheshort-circuitheatlossfactor,PLF Theremaining17%includeshotels,schools,hospitals sc m isthepart-loadfactorduringdesignmonth,q isthe and leisure facilities (Choudhary, 2012). The inten- a netannualaverageheattransfertotheground(W),q sityofheatingandcoolingdemandperbuildingtype lh 5 Table 1. Conditions and assumptions in bhe design for planningparametricstudy. Parameter Unit Value Justification Coefficientof / 3.3 Kavanaughand Performance(COP) Rafferty,1997 EnergyEfficiency / 4.2 Kavanaughand Ratio(EER) Rafferty,1997 Short-circuitHeat / 1.04 Kavanaughand LossFactor(F ) Rafferty,1997 sc LiquidTemperature K 278.5 ChosenDesign atheatpumpinlet value forHeating(t ) wi LiquidTemperature K 275.0 Estimatebased atheatpumpoutlet ontypical forHeating(t ) temperaturedrop wo LiquidTemperature K 300.0 ChosenDesign Figure1. Landusetypedistributionsofbuildingsinwest- atheatpumpinlet value minster. forCooling(t ) wi LiquidTemperature K 308.0 Estimatebased atheatpumpoutlet ontypical ineast-westandnorth-southdirectionsand1minthe forCooling(t ) temperaturedrop verticaldirection.Inthecasestudy,theaveragether- wo MinimumBorehole m 6 MIS(DECC, malpropertyvaluewithinthedepthof150mofeach Spacing 2008)a gridwasestimatedtodevelopthethermalconductivity BoreholeDiameter mm 130 MIS(DECC, andthethermaldiffusivitymapsofWestminster. 2008)a Forthegroundtemperature,thegroundtemperature PipeDiameter mm 32mmOD MIS(DECC, of London was used. Headon et al. (2009) gave the SDR-11 2008)a undergroundtemperatureinformationofLondoncity TChoenrdmuacltivity W/m.K (0P.4E20100) 2M0I0S8)(aDECC, basedonthewelldataas12.3◦Cat60mdepth,12.8◦C ofPipe at80mdepthand13.1◦Cat100mdepth.Accordingly, PipeCentre-Pipe mm 52 MIS(DECC, the ground temperature in the design was set to be CentreShank 2008)a 12.8◦C,whichwasconsideredastheaverageground Spacing temperaturevaluewithinthedepthof150m. ThermalTransfer / 25%Mono MIS(DECC, SizingHeatpumpisakeyintermediatestepinthe Fluid Ethylene 2008)a GHE design calculation. A database of heat pumps Gylcol within capacity range of 5–75kW is therefore also includedwithinthemodel.Iftherequiredcapacityis a. MIS (Microgeneration Installation Standard), DECC outside of this range, a combination of two or more (DepartmentofEnergyandClimateChange,UK)(2008). heat pumps is used. In the design calculation, the temperaturepenaltyt isusedasaparametertocon- p siderthermalinterferenceofadjacentboreholeswith (inkWh/m2 peryear)wasgatheredfromDECCcer- reasonableboreholearrangements.Hence,withinthe tificates(compiledandreleasedbytheUKCentrefor run time, there is temperature decrease surrounding SustainableEnergy),CharteredInstitutionofBuilding theborehole,andthetemperaturereductiondecreases ServicesEngineersGuideFandTM46(CIBSE,2004, withtimeastransientstate.Itisassumedthatnoheat 2008)and2011energydistributioncharts(EDCs).The is diffused out of a square cylinder with sides equal design heating block load per building (q in kW) lh to the borehole separation distance (Kavanaugh and wasestimatedbymultiplyingtheheatingdemandper Rafferty,1997). buildingtypeinkWh/m2peryearwiththefloorarea ofabuildinganddividingbythenumberofheating hoursinayear(2160hinthiscase,assuming12hof 3.3 Boreholelocationscenarios heatingperdayforhalftheyear).Coolingestimation isperformedinthesameway. Inthiscasestudy,therequirednumberofboreholesfor The thermal conductivity and thermal diffusivity eachbuildingwasallocatedataspatialposition.Two mapsweredevelopedbasedonthegeologicalmapand scenarios were considered: (a) under building (Fig- thethermalpropertylook-uptable.Thesoildistribu- ure2a)–withintheland-areaoftheexistingbuilding, tionmapoftheCityofWestminsterwasobtainedfrom and(b)aroundthebuilding(Figure2b)–onthebuffer theBritishGeologicalSurvey(BGS)geologicalmap areawiththebuildingboundaryasthemidline.The ofLondon.Foreachtypeofsoil,itsthermalconductiv- shapedpolygonsandthepointsstandforthebuildings ityandthermaldiffusivitywereassignedaccordingto and the installed boreholes, respectively. In order to thelogsfromsiteinvestigationworkbyBGS.Ather- avoid thermal interference, the spacing between any malconductivitymapandathermaldiffusivitymap twoboreholeswasfixedat6metres,aspertheMIS were then developed with grids of size 50m×50m (DECC, 2008). This means that no heat is diffused 6