Using reflective pavements to mitigate urban heat island in warm climates - Results from a large scale urban mitigation project

2018·6.3 MB·English

by  G. E. Kyriakodis

UrbanClimate24(2018)326–339
ContentslistsavailableatScienceDirect
Urban Climate
journalhomepage:http://www.elsevier.com/locate/uclim
Using reflective pavements to mitigate urban heat island in
warm climates - Results from a large scale urban
mitigation project
G-E.Kyriakodisa,*,M.Santamourisa,b
aGroupBuildingEnvironmentalStudies,PhysicsDepartment,UniversityofAthens,Athens,Greece
bTheAnitaLawrenceChairinHighPerformanceArchitecture,SchoolofBuiltEnvironment,UniversityofNewSouthWales,Sydney,Australia
A R T I C L E I N F O A B S T R A C T
Articlehistory: UHIisthemoststudiedphenomenonofclimatechangeandreferstotheincreasedambi-
Received14October2016 enttemperatureofcitiescomparedtoruralsettings.Implementationofreflectivematerials
Receivedinrevisedform3February2017 tourbanstructures,suchasroadsandpavements,reducesthesurfaceandambienttemper-
Accepted7February2017 atureandcontributestocounterbalancetheimpactofthephenomenon.Thepresentpaper
Availableonline10February2017
describesthedesignandtheexperimentalevaluationofalargescaleimplementationofcool
asphalticandconcretepavementsinamajortrafficaxisofWesternAthenscoveringatotal
Keywords: zone of 37,000m2. To our knowledge, this project is one of the largest urban mitigation
Heatisland projectsintheworld.Extendedmonitoringwasperformedintheareaduringtheentiretyof
Coolmaterialsandpavements thesummerperiod,whileComputationalFluidDynamics(CFD)simulationwasusedtoeval-
Coolcolouredthinlayerasphalt
uatethethermalimpactoftheapplication.Itwasconcludedthattheuseofcoolnon-aged
Photocatalyticpavements asphaltcanreducetheambienttemperaturebyupto1.5◦Candthemaximumsurfacetem-
Heatislandmitigationtechniques
peraturereductioncouldreach11.5◦C,whilethethermalcomfortconditionscanimprove
Urbanclimaticchange
considerably. Ageing phenomena may reduce substantially and up to 50% the mitigation
potentialofcoolasphalticmaterials.
©2017ElsevierB.V.Allrightsreserved.
1. Introduction
Theurbanheatislandphenomenonreferstotheincreaseoftheambienttemperatureofcitiescomparedtotheirsurrounding
suburbanandruralenvironment.Increasedurbantemperatureistheresultofthepositivethermalbalanceofcitiescaused
by the additional heat released and stored in the urban structure, and the lack of low temperature environmental sinks
(Santamouris,2001).Theurbanheatislandisthemoststudiedphenomenonofclimatechange,andtherearemorethan400
citiesaroundtheworldwhereexperimentaldocumentationisavailable(Santamouris,2015a,2016b).Theamplitudeofthe
phenomenonvariesasafunctionofthelocalcharacteristicsandofthestrengthoftheheatsourcesandmayexceed6–7K
(SantamourisandKolokotsa,2016).
Local climate change has a significant impact on the energy consumption of buildings, it increases the concentration
of local pollutants, deteriorates indoor and outdoor thermal comfort conditions, increases the vulnerability of low-income
*Correspondingauthor.
E-mail address:[email protected](G.-E.Kyriakodis).
http://dx.doi.org/10.1016/j.uclim.2017.02.002
2212-0955/©2017ElsevierB.V.Allrightsreserved.
G-E.Kyriakodis,M.Santamouris/UrbanClimate24(2018)326–339 327
population and affect health conditions, while it raises the global ecological footprint of cities (Baccini et al., 2008;
Pantavou et al., 2011; Sakka et al., 2012; Santamouris, 2015b; Santamouris and Kolokotsa, 2015; Santamouris et al.,
2007; Stathopoulou et al., 2008). Recent studies have shown that the urban heat island increases the peak electricity
demand during the summer period between 0.45% and 4.6% per degree of temperature increase (Santamouris et al.,
2015b), while the annual energy consumption for cooling may increase up to 100% (Hassid et al., 2000; Santamouris
etal.,2001).Compilationoftheexistingdataontheenergypenaltyinducedbytheurbanheatislandhasshownthatitisclose
to0.8kWhperunitofcitysurfaceanddegreeoftemperatureincreaseoralmost68kWhperpersonanddegree(Santamouris,
2014b).
Forecastsoffuturecoolingenergyconsumptionofresidentialandcommercialbuildingsrevealthatby2050itmayincrease
upto750%and275%,respectively,becauseofthelocalandglobalclimatechange,thetremendousincreaseofthepopulation
andtheexpectedincreasepenetrationofthecoolingsystemsaroundtheworld(Santamouris,2016a).Tocounterbalancethe
temperatureincreaseintheurbanenvironmentandreduceasmuchaspossibleitsimpactonenergyandenvironment,advanced
and efficient mitigation technologies have been developed and applied widely (Akbari et al., 2016). Proposed mitigation
technologiesinvolvetheuseofreflectivematerialstosolarradiation,additionalurbangreeneryintegratedintobuildingsand
thecitystructure,dissipationoftheexcessurbanheatintolowtemperatureheatsinkslikethegroundandthewater,solar
shading,reductionoftheanthropogenicheatanduseofevaporationtechnologies(AkbariandKolokotsa,2016).
Highly reflective materials to solar radiation when used in the urban environment present a significantly lower surface
temperature and contribute to reducing the sensible heat released in the atmosphere and mitigating the urban heat island
(Doulosetal.,2004).Reflectiveorcoolmaterialsmaybeusedontheroofsofurbanbuildings,coolroofs,andaspavements
intheopenurbanspaces,coolpavements.Severaltypesandtechnologiesofcoolmaterialsforbuildingsandpavementshave
been developed involving reflective materials in the visible or infrared part of solar radiation (Synnefa et al., 2007, 2006),
thermochromiccoatings(Karlessietal.,2009),reflectiveasphalticproducts(Synnefaetal.,2011)reflectivemembranesand
retroreflectivematerials(Piselloetal.,2016;Rossietal.,2015;Santamourisetal.,2011),etc.Analysisoftensofstudiesand
largescaleapplicationshaveshownthattheuseofcoolmaterialsintheurbanenvironmentmaydecreasetheaverageandpeak
ambienttemperatureupto1.0Kand2.5Krespectively(Santamouris,2014a).
Thedevelopmentofreflectiveand/orperviouspavementmaycontributesignificantlyreducingtheurbantemperatureand
mitigating the urban heat island. Several technologies of reflective pavements have been developed and are commercially
available while important research is carried out on the topic (Santamouris, 2013). Hundreds of large scale applications of
reflectivepavementsareavailablearoundtheworldandtheirexperimentalevaluationshowsthattheirmitigationpotential
isquitehigh(Castaldoetal.,2015;Fintikakisetal.,2011;Gaitanietal.,2011;HuynhandEckert,2012;OMalleyetal.,2015;
Santamourisetal.,2012;Tumini,2014;Wangetal.,2016b).Arecentanalysisof15largescalemitigationprojectsinvolvingthe
useofvarioustypesofreflectivepavementshasshownthattheaverageandthepeaktemperaturedropachievedwas1.3Kand
2.5K,respectively(Santamourisetal.,2016),whiletheaverageandpeaktemperaturedropsper10%increaseofthealbedowas
closeto0.27Kand0.94K.
TheexistenceandthecharacteristicsoftheurbanheatislandphenomenonisverywelldocumentedinthecityofAthens,
Greece (Livada et al., 2002; Mihalakakou et al., 2004). The phenomenon is more intense in the Western part of the city
characterizedbyhighurbandensity,increasedanthropogenicheat,andlackofgreenspaces,anditsmagnitudemayexceed
6–7K (Giannopoulou et al., 2014; Mihalakakou et al., 2002). To counterbalance the significant impact of the high ambient
temperaturesinthearea,alargescalerehabilitationprograminvolvingtheuseofvariousmitigationtechnologieshasbeen
designedandimplemented(Santamourisetal.,2015a).
Thepresentpaperpresentsthedesignandtheexperimentalevaluationofalargescaleimplementationofcoolasphaltic
andconcretepavementsonamajortrafficaxisofWesternAthens,coveringatotalzoneof37,000m2.Theprojectis,toour
knowledge,oneofthelargesturbanmitigationprojectsintheworld.
2. Descriptionofthesite
Therehabilitativeareaisthemaintrafficaxis(ThivonAvenue)oftheMunicipalityofEgaleo,situatedinthewesternsuburbs
ofAthenswiththelongaxisinaNE(cid:3)N-SW(cid:3)Sdirection(67◦fromrealNorthcounter-clockwise)asFig.1depicts.Thegeometrical
characteristicofthetrafficaxiswasL/W=8.Itconsistsoffourtrafficlanesseparatedwitharefugeislandwithplantedtrees
along its axis. Furthermore, both sides of the road are covered with pavements and there are three-to four-story buildings
adjacenttothem,whichcharacterizetheareaasamixedresidentialandindustrialzone.Theaxissupportsintensivetraffic
whiletheanthropogenicheatreleasedisquitehigh.Theroadwasinitiallycoveredwithconventionalblackasphalt,whilegrey
concretetileswereusedaspavements.Theclimateoftheareacorrespondstoveryhotanddrysummersanditisinfluencedby
thepresenceofmountEgaleowhichactsasanaturalobstacleagainstthenorthernwinds,whichdominateduringthesummer
periodintheAthensarea.Detailedclimaticmonitoringofthearea,hasshownthatthespecificurbanzonepresentsthehigh
ambienttemperatureinthecityofAthens(Giannopoulouetal.,2011).TheprojectwascarriedoutbythePrefectureofAthensin
collaborationwiththelocalMunicipalityandwasbuiltbetween2014and2015.Therenovationcoversatotalareaof37,000 m2
andisthegreatestrecordedinGreece.Itinvolvestheimplementationofapproximately18,000m2ofcoolcolouredthinlayer
asphaltandofapproximately19,300m2ofreflectiveconcretepavements.
328 G-E.Kyriakodis,M.Santamouris/UrbanClimate24(2018)326–339
Fig.1. Orientationofrehabilitativearea,Egaleo,Athens.
3. Characteristicsoftheinstalledreflectivepavements
Pavementmaterialswereselectedinorderto:
(a) Improveasmuchaspossiblethethermalconditionsinthearea,mitigatetheurbanheatislandandenhancethermal
comfortconditions.
(b) Ensuringdrivingsafetybyavoidingundesirablecontrastlevelsandglare.
(c) Ensuringtheenvironmentalremediationbyreducingmotorvehicleairpollutants(NO ).
2
Tosatisfytheaboveobjectives,theexistingblackconventionalasphaltpresentingasolarreflectanceSRcloseto0.04was
replacedbyalightyellowthinlayerasphaltcharacterizedbySR=0.35andanemissivitycloseto0.9(Fig.2).Toavoidproblems
ofcontrastandglare,thematerialwasdesignedtopresentmuchhigherreflectivityinthenearinfraredthaninthevisiblepartof
thesolarradiation(Table1).Theyellowthinlayerasphaltwasdevelopedbymixinganelastomericasphaltbinderwithinfrared
reflectivepigmentsandaggregatesandthefinalapplicationwasachievedwithslurrysurfacingtechnique.
Inparallel,thegreyconcretepavementswerereplacedbywhiteconcretepavements(SR=0.66)mixedwithpigmentsof
TiO .ThespectralreflectanceofthepavementsisgiveninFig.3,whileapictureofthepavementtilesinthevisibleandinfrared
2
is given in Fig. 4. The infrared emittance of the pavements was measured as close to 0.9, according to the ASTM Standard
E408-71:StandardTestMethodforTotalNormalEmittanceofSurfaces.Whenexposedtosunlightandinthepresenceofalow
concentrationofwatermolecules,TiO containedwithinthepavementsgenerateshydroxylradicals(OH),apowerfuloxidizing
2
agent.Theseradicalspromotetheoxidationofavarietyoforganicandinorganicpollutants(Wangetal.,2016a).Notably,the
photocatalyticpropertyofthesepavementsresultedtoa15%inoxidationofNO toNO (Fig.5).
X 3
Theageingofthematerialsandinparticularthepotentialopticaldegradationanddecreaseofthereflectivitywasassessed
throughcontinuousmonitoringoftheiropticalperformance.Thespectralreflectancesofthematerialsweremeasuredinthe
Materials Lab of theUniversityofAthens,using a UV/vis/NIRspectrophotometer(Varian Carry 5000)fittedwitha 150mm
diameterintegratingspherethatcollectsbothspecularanddiffuseradiation,accordingtotheASTMStandardE903-96:Standard
TestMethodforSolarAbsorptance,ReflectanceandTransmittanceofMaterialsUsingIntegratingSpheres.Itwasfoundthatafter
sixmonthsofcontinuoususe,thereflectivityofthecoolasphaltwasreducedfrom0.33to0.17(Fig.6).Decreaseofthesolar
reflectanceisattributedtothedepositionofrubberfromthetyresofcarsonthesurfaceofcoolasphalticmaterialsjustafter
theirinstallation(Synnefaetal.,2011)andalsotothedecreaseofthereflectivityofthecoolpavementsbecauseofthedeposition
ofseveralatmosphericpollutantsontheirsurface(Mastrapostolietal.,2016).Itisobservedthatthecoolasphalticmaterial
recoverstheinitialreflectivityalmostfully,(SR=0.33),whenscrubbingitwithwetsolvent(H O).Inordertofurtherinvestigate
2
thespecificopticaldegradationoftheasphalticmaterial,FourierTransformInfraredspectroscopytechniqueswereusedtotest
thecleanerandthepollutantsample.FTIRmeasurementsidentifiedtheexistenceofadditionalthreebandvibrationsat:3422.3,
1028.96,470.21cm−1whichlabelN–H,C–NandPb–Obondsrespectively.Itisconcludedthatthecontaminatedsampleswere
G-E.Kyriakodis,M.Santamouris/UrbanClimate24(2018)326–339 329
Fig.2. Apictureoftheinstalledyellowthinlayerasphalt.
polluted by the particle compounds of motor vehicle emissions and the deposition of the tyres of vehicles. Contrary to the
asphalticmaterial,thevariationofthesolarreflectivityoftheconcretepavementswasalmostinsignificant.
4. Monitoringcampaignandexperimentalassessment
Theexperimentalassessment,exceptforthelaboratorymeasurementspresentedabove,includedanextensivemonitoring
strategyofinsitumeasurementsinthearea.Thence,adetailedmonitoringcampaignwasscheduledinordertoevaluatethe
impactoftheimplementedcoolpavementsinthemicroclimateoftheareaandtodocumentthethermalperformanceofthe
selectedmaterialscomparedtotheconventionalones.Thenecessaryvaluesfortheboundaryconditionsofthethermalmodel
werealsorecorded.
ThemonitoringcampaignwasperformedduringtheentiretyofthesummerperiodofMay–September2015andatleast
threerecordspermonthwerecarriedoutbasedonthesameexperimentalprotocol.Theoutdoorclimaticconditionsofthe
experimentalperiodwerecharacterizedbyveryhotdays(approximatingaheatwave)andtypicalclearskyconditions.We
emphasizedthetimeintervalbetween12:00and17:00LST,duetothesebeingthehoursofmaximumsolarradiationand,
consequently, the hours of maximum solar gains. Measurements of the ambient temperature and relative humidity were
recorded with a data logger at a height of 1.5m, placed in a thermometer shelter near the traffic axis. The accuracy of the
thermometerwas±0.1K.Inparallel,theinstantaneousvaluesofsurfacetemperaturesweremeasuredattimestepsof30min
(Fig.7).Thesamplepointsofmeasurementswerealwaysthesame,selectedfornotbeingshadedandprovidingassuredaccess
todifferenttypesofasphalt.Itisworthstatingthateverytwoweeks,thecoolcolouredasphaltwascleanedbymeansofwet
solvent(H O)scrubsatleastonedaybeforetheinitialmeasurementinordertoeliminateevaporationeffects.Thereference
2
pointswerethefollowing:
Table1
Solarreflectancevalues(SR,300–2500nm)andsolarreflectancevaluesintheUV(300–400nm),vis(400–700nm)and
IR(700–2500nm)partofthespectrumofcoollightyellowandconventionalblackasphalt.
Sample SR SRUV SRVIS SRNIR
Lightyellowasphalt 0.35 0.11 0.24 0.42
Conventionalblackasphalt 0.04 0.04 0.03 0.04
330 G-E.Kyriakodis,M.Santamouris/UrbanClimate24(2018)326–339
Fig.3. Thesolarreflectanceoftheimplementedpavements.
1. S conventionalblackasphalt
1
2. S conventionalfaintasphalt
2
3. S lightyellowcoolasphalt
3
4. S lightyellowcoolcontaminatedasphalt
4
5. S coolphotocatalyticpavement(colouredwhite)
pl
6. Sgreyconventionalpavement(colouredgrey).
Theinstrumentsusedtodepictsurfacetemperaturedifferencesamongsamplepointswereaninfraredcamera(AGEMA
Thermovision570,7.5–13lmwavelength)andavisualIRThermometer(FlukeVT02).Theambientclimaticconditionswere
alsorecorded,whileclimaticdataaroundtheexperimentalsite,includingambienttemperature,relativehumidity,windspeed
anddirection,globalanddirectsolarradiationonahorizontalsurfacewerecollectedfromthreemeteorologicalstationsofthe
NOA(NationalObservatoryofAthens).
5. Monitoringresults
Onsitecomparativemeasurementsrevealedthattheaveragesurfacetemperatureofthereflectiveasphaltoverthecool-
ingperiodisbyupto7.5◦Clowerthanthecorrespondingsurfacetemperatureoftheconventionalasphalt.Insomecasesof
extremelyhotconditions,themaximumtemperaturedifferencebetweenthereflectiveandconventionalasphaltcouldreach
11.5◦C.AlmostsimilarresultsarereportedinSynnefaetal.(2011),CarnieloandZinzi(2013),KawakamiandKubo(2008),
Kondoetal.(2008),Nishiokaetal.(2006).Fig.8reportsthemeasurementstakenonthe18thofJuly,consideredasthemost
representativedayofmeasurementsfortheentiresummer.
Fig.4. Infraredandvisibleimagesofcoolphotocatalyticpavements(18/07/2015,14:30LST)onsite.
G-E.Kyriakodis,M.Santamouris/UrbanClimate24(2018)326–339 331
Fig.5. Thephotocatalyticpropertyoftheimplementedpavements.
Surface temperatures are found to present the same diurnal trend. Specifically, the maximum surface temperature of
theblackconventionalasphaltwas68.5◦C,at15:30while,atthesametime,thereflectivelightyellowasphaltwasalmost
8.9◦Clower,thusreaching59.6◦C.Duringthemeasurementperiod,thedifferencesbetweenthereflectiveandconventional
asphalt, varied between 7.5 and 8.9◦C and the average surface temperature difference was 8.3◦C. In parallel, the surface
temperatureofthepollutedreflectiveandoftheconventionalfaintasphaltspresentedasimilartemporaltrend.Maximum
surfacetemperaturesweremeasuredataround63.1◦Cand64.8◦Crespectively.Theaveragesurfacetemperaturereduction
was close to 1.7◦C. Notably, the corresponding decrease depends on the sample point. In general, the relative decrease of
thecoolingperiodisapproximately3.0◦C.Fluctuationsinmeasuredvaluescorrespondtowindgusts.Thedailyvariationof
theconcretepavementsfollowedthesametrendastheasphalticmaterials.Theaveragesurfacetemperaturedecreaseofthe
reflectivepavementswasmeasuredcloseto6.1◦C,comparedtotheinitiallyinstalledconcretepavement(Fig.9).
Inparallel,theaverageambienttemperatureduringthemeasurementtimeinterval(10:00–18:00)intheareaextracted
bythesensornearthetrafficaxisandat1.5mheightwas32.8◦Cwhilethemaximumvaluewasrecordedat16:30reaching
34.5◦C.Relativehumiditymeasurementsrangedbetween22.3%(minimum15:30)and40%(maximum11:00)presentingan
averageof27.1%forthesametimeinterval(Fig.10).Thecorrespondingmeasurementsofthenearestmeteorologicalstation
(elevation:50m)alsorecordedthemaximumat16:30presentingavalueof33.5◦C,whiletheaverageambienttemperaturefor
thereferencedtimeintervalwas32.5◦C.Asconcernssolarradiation,themaximumvaluewasrecordedat15:00reachingthe
valueof844W/m2.
Fig.6. Solarreflectanceofclean(blue)andpolluted(red)coolasphalt.
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4
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3
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6
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Fig.7. Infraredandvisibleimagesoftheconventionalblack(a),upstreamcool(b),downstreamcool(c)andcomparisonbetweenthem(18/07/2015,14:00LST)onsite. 9
G-E.Kyriakodis,M.Santamouris/UrbanClimate24(2018)326–339 333
Fig.8. ComparisonofthemeasuredsurfacetemperaturesoffourdifferentasphaltsamplesattheupstreaminThivonAvenueon18thofJuly.Blackcurve
depictsambienttemperaturebase.
6. Assessingthemitigationperformanceandthethermalimprovementsintherehabilitatedurbanzone
Adirectcomparisonoftheexperimentalmeasurementsperformedbeforeandaftertheclimaticrehabilitationofaplaceis
notpossiblegiventhatmeasurementsaretakenundercompletelydifferentclimaticandboundaryconditions.Toovercome
the problem, a specific methodology was proposed and applied in Santamouris et al. (2012). According to the proposed
methodology, the collected experimental data are used to validate a numerical simulation model developed to predict the
thermalperformanceintheconsideredarea.Themodelisthenusedtosimulatethethermalconditionsintheareabeforeand
aftertherehabilitationusingexactlythesameclimaticandboundaryconditions.Acomparisonofthetwosetsofcalculated
datapermitstoassesstheachievedthermalimprovementsintheconsideredarea.
AmodeloftheurbanzonewithallspecificdetailshasbeendevelopedusingtheEnviMetSoftware(Bruse,2004).ENVI-met
is a three-dimensional microclimate model designed to simulate the surface-plant-air interactions with the urban environ-
ment.ItisbasedonReynoldsAveragedNavier-Stokes(RANS)equations,withanon-hydrostatic,micro-scale,obstacle-resolving
model and advanced parameterizations for simulation of surface-plant-air interactions in urban environments. ENVI-met
providesbothspatialresolution(0.5–10m)andtemporalvariation(finest10sresolution)foranurbanboundarylayerclimate.
Additionally,ENVI-methasfeaturesnotcommonlyavailableinotherCFDdispersioncodes(e.g.adetailedmicroclimatemodule
andavegetationmodule).Therequiredinputincludesmeteorologicaldataanddomaincharacteristics.
Fig.9. Comparisonofthemeasuredsurfacetemperaturesofdifferentpavementsampleson18thofJuly.Blackcurvedepictsbaseambienttemperature.
334 G-E.Kyriakodis,M.Santamouris/UrbanClimate24(2018)326–339
Fig.10. Ambientclimaticconditionsforthe18thofJuly.
Fig.11. Geometryandcalculationdomain(a),satelliteimage(b)ofthesimulatedarea.
Thephysicaldimensionsofthesitecorrespondtoa1800(x)×224(y)×150(z)mandthecalculationdomainconsistsof
576×80×30cellsateachaxisrespectively(Fig.11).Throughthelimitedresolutionthatthenoncommercialbasicversion
provides,themaindomainwassplitintothreesub-areasofequidistancelengtheach.Thescenarioofchangingthehorizontal
gridsize(dx,dy)wasdeemedunacceptable.Otherwise,itwouldhavebeennearimpossibletoconsidertheplantedrefugeisland
whichhasgreatimpactonsurfacetemperatures.Therefore,thedimensionsofeachsub-areaconsistof192×80×30cells.Note
thatthemodelareaisrotated293.4◦outofgridnorth.Inordertoavoidnumericalproblemsbecauseoftheinterferenceofthe
modelborderswithinternalmodeldynamics,sevenadditionalnestinggridswereincluded.Concerningturbulence,the1.5order
E-epsilonturbulenceclosuremodelisused.Attheoutflowandlateralboundaries,azerogradientconditionwasused,whileat
Table2
Inputdataoftheconfigurationfile.
Buildingproperties Values
Insidetemperature[K] 301
Heattransmissionwalls[W/m2K] 1.1
Heattransmissionroofs[W/m2K] 1.1
Albedowalls 0.2
Albedoroofs 0.2
G-E.Kyriakodis,M.Santamouris/UrbanClimate24(2018)326–339 335
Fig.12. Hourlysimulatedvs.measuredairtemperatureforthe14thofJune.
thetopboundary,allverticalmotionswereassumedtobezero.Thecalculationofthevariationsoflateralboundaryconditions
(LBC)oftemperatureandhumiditywaschosentobethe“open”method.Withthismethod,thevaluesofthenextgridpoint
closetotheborderarecopiedtotheborderateachtimestep(KawakamiandKubo,2008).Thevariationoflateralboundary
conditionofkineticenergyoftheairinflowwasinsteadcalculatedwiththe“forced”methodbywhichthevaluesoftheone
dimensionalmodelarecopiedtotheborder.Inaddition,fortheaccomplishmentoftheconfigurationfile,importsconcerning
insidetemperatureandthermophysicalpropertiesofthebuildingswereintroduced,asshowninTable2,inaccordancewith
thecharacteristicsofthemajorityofthebuildingsinthesite.
Simulationswereperformedfordifferentmeasuredboundaryconditionsinordertobettercorroboratetherealconditions.
Thus,the14thofJunewaspreferredbecauseitappearedtohaveanincreasedambienttemperatureandbetterpresentedthe
summerclimaticconditionsinthearea.Thewindataheightof10mwasmeasuredtobealeadingnorthwindof1.9m/s,
whiletheroughnesslength(z )wasestimatedtobe0.6accordingtoBruseandFleer(1998).Thesolarradiationadjustment
0
factorwassetto0.9tosimulatetheintenseradiationlevelofthespecificclearsummerdayinAthens.Fortheinitialairtem-
perature,thevalueof305.5Kwasused.Threescenariosaresimulated.Thefirstscenariocorrespondedtotheinitialconditions
beforetheclimaticrehabilitation,thesecondandthirdscenariosdescribedthespecificconditionsaftertherehabilitationtaking
intoaccountorneglectingtheopticaldegradationofthematerialsrespectively,(coolandagedcoolscenarios).Thecalculated
distributionofthesurfaceandambienttemperature,asobtainedfromthesecondscenario,werecomparedwiththecorre-
spondingmeasurementsinordertoachievethebestpossiblecalibrationofthemodel.Anacceptableagreementbetweenthe
experimentalandtheoreticalresultswasobtainedandthemaximumdifferenceoftheambientandsurfacetemperaturesdid
notexceed0.4Kand0.8K,respectively.Fig.12presentsthecorrelationbetweenthesimulatedandmeasuredvaluesofthe
ambienttemperature.TheR2indexwascalculatedequalto92.7%.
Sincethemodelwascalibratedandvalidated,simulationswereperformedforthethreescenariosasmentionedaboveand
foreachsub-arearesultinginninefinalsimulationsintotal.Simulationshaveshownthattheimplementedreflectiveasphaltic
materialcaneffectivelyreducethesurfacetemperaturesonasummerday,evenifitsreflectivityisreducedbecauseofthe
ageingprocesses.Inparticular,thenonagedasphalticmaterial,(albedoof0.35),presentedupto9.0Klowertemperaturethan
theconventionalasphalt,(Table3),whiletheloweralbedoasphalt,(albedoof0.17),hadupto6Klowersurfacetemperature
thantheconventionalmaterial(Table4).Inparallel,thesurfacetemperatureoftheconcretepavements,(albedo0.66),found
topresentupto6Klowertemperaturethantheconventionalgreypavementmaterials.Fig.13,presentsthepredictedspatial
distributionofthesurfacetemperaturesineachsub-area(14:00,14/06/2015)fortheprevious(conventional),current(cool
aged)andideal(coolcleaned)conditionverticallyarranged.Thelasthorizontalsetdepictsthespatialdistributionofabsolute
differencesinsurfacetemperaturesbetweencoolcleanedandconventionalmaterials.
Asconcernsthedistributionoftheambienttemperatureintheconsideredarea,simulationshaveshownthattheapplication
of the reflective pavements can significantly reduce the local air temperature. When the non aged asphaltic materials,
(SR=0.35) and the cool pavements are considered, cool scenario, the average maximum ambient temperature drop was
close to 1.5◦C. For the conventional scenario, the ambient temperature at 1.5m height is found to range between 32.9◦C
Table3
Measuredandpredictedsurfacetemperaturedifferencesofconventionaland
coolasphaltforthefirstsubarea.
Time Asphalttemperature(◦C)
DTConvmeasured DTConvpredicted
Cool Cool
12:00 7.3 7.4–7.9
14:00 8.2 8.2–9.0