NumericalModellingof
ShallowGeothermalEnergySystems
Shallowgeothermalenergysystemsusethe
groundrelativelyclosetothesurfaceasa
sourceandsinkforthermalenergytoheatand
coolbuildingssustainably.
Geothermalenergyisavailableona24/7basis,
soitmaybeconvenientlyandeconomically
usedwithamuchreducedcarbonfootprint.
TherelativelyhighinstallationcostsofGHEs
makeGSHPsystemsstruggleforamore
widespreadworldwideadaptionofthe
technology.Therefore,amoreaccurateand
powerfulmodellingtoolisdesirabletohelp
designGHEsmoreefficiently.Inorderto
numericallysimulatetheheattransferred
betweenthegroundandthecarrierfluidwithin
thepipesinaGHE,3DGHEsystemshavebeen
modelledusingthefiniteelementpackage
COMSOLMultiphysics.Thegoverningequations
forfluidflowandheattransferarecoupled
numericallytoevaluatethethermal
performanceoftheGHEs.Thisfigureshows
examplesofGHEs,andinitialandboundary
conditionsonthe3Dmesh.
ThenewmodelsdevelopedbytheUniversityof
Melbournearebeingusedtoinvestigatethe
effectsofdifferentdesignparametersonthe
thermalperformanceofGHEs.Steady‐stateand
transientanalysesareconductedondifferent
parameters.Herethesteady‐stateeffectofGHE
lengthoncarrierfluidtemperature isshown.
LGHE increasing
ResultsobtainedbyAsalBidarmaghz.ShereceivedaPhDin2015
Whileaccurate,3DFEMmodelsare
computationallyexpensive.Faster,simpler
spreadsheetmodelswerealsodevelopedto
modeltypicalcases,yetmaintaining
reasonableaccuracy.OurCFES(Conductive
FluxandEnergySystem)modelallowsusto
runsingleverticalheatexchanger
simulationshundredsoftimesfasterthan
ourdetailedFEM3Dmodels.Thetradeoff
liesonthelossofflexibilityintheGHEpipe
configuration.
A78dayGSHPtestvspredictionsoftheCFESmodel
HCFESisanextensionoftheCFESmodel
developedforhorizontalslinkyGHEsor
multiplehorizontalstraightHDPEpipes. It
isequallybasedonenergyconservation
aroundconcentricvolumesofground
surroundingtheGHE,asintheCFES.These
finitedifferenttypemodelsdonotrequire
theestimationof“thermalresistances”but
rathertheactualthermalparameters
(conductivity,diffusivity,ground
temperature)andareavailablein
spreadsheetsforeasyaccesstomost
engineers.
ModellingprinciplesbehindtheHCEFSmodel
ResultsobtainedbyStuartColls.HereceivedaPhDin2014
AhybridmodelbetweenFEMandsimple,
accessibleevaluationstoolsforthermal
resistance,fortheuseofavailableanalytical
solutions,derivedinaGGHE(Generalized
GroundHeatExchanger)model.Here,a
graphical“fluxnet”thermalapproachis
introducedtoevaluatesuchthermal
resistanceinGHEsofvariousgeometries.
Examplecomparisonbetween
experimentaldata(ground
heatingandunforcedcooling)and
theGGHEmodelcomputations
ResultsobtainedbyAmirKivi.PhDthesisunderexamination
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