Energy efficiency evaluation of zero energy houses

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ContentslistsavailableatScienceDirect

Energy

and

Buildings

jo u r n al h om ep a g e :w w w . e l s e v i e r . c o m / l o c a t e / e n b u i l d

Energy

efficiency

evaluation

of

zero

energy

houses

Edwin

Rodriguez-Ubinas

a,∗

,

Sergio

Rodriguez

a

,

Karsten

Voss

b

,

Marija

S.

Todorovic

c aDepartmentofConstructionandTechnologyinArchitecture(DCTA),SchoolofArchitecture,TechnicalUniversityofMadrid(UPM),Av.JuandeHerrera4, 28040Madrid,Spain

bDepartmentofArchitecture,BuildingPhysicsandTechnicalServices,BergischeUniversitätWuppertal,HaspelerStraße27,42285Wuppertal,Germany cMultidisciplinaryStudiesProgram,UniversityofBelgrade,Serbia

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Availableonline7July2014 Keywords: Energyefficiency Interiorcomfort Passivestrategies Passivedesign Solardecathlon Solarhouses Energyconsumption Zeroenergy

a

b

s

t

r

a

c

t

Giventheglobalenergyandenvironmentalsituation,theEuropeanUnionhasbeenissuingdirectives withincreasinglydemandingrequirementsintermoftheenergyefficiencyinbuildings.The interna-tionalcompetitionofsustainablehouses,SolarDecathlonEurope(SDE),isalignedwiththeseEuropean objectives.SDEhousesarelowenergysolarbuildingsthatmustreachtheneartozeroenergyhouses’ goal.Inthe2012edition,inordertoemphasizeitssignificance,theEnergyEfficiencyContestwasadded. SDEhouses’interiorcomfort,functioningandenergyperformanceismonitored.Themonitoringdata cangiveanideaabouttheefficiencyofthehouses.However,ajurycomprisedbyinternationalexperts isresponsibleforcarryingoutthehousesenergyefficiencyevaluation.Passivestrategiesandhouses servicesareanalyzed.Additionally,thejury’sassessmenthasbeencomparedwiththebehaviorofthe housesduringthemonitoringperiod.Comparativestudiesmakeemphasisontheenergyaspects,houses functioningandtheirinteriorcomfort.Conclusionsincludethoughtsrelatedwiththeevaluationprocess, theresultsofthecomparativestudiesandsuggestionsforthenextcompetitions.

©2014ElsevierB.V.Allrightsreserved.

1. Introduction

Thetermefficiencyisgenerallydefinedastherelationbetween

thematerials,energyorresourcesneedtoperformataskorprovide

aservice,andthefinalresult.Energyefficiencyimprovementis

regarded asany action undertakenby a producer orconsumer

of energy products that reduce energy use per unit of output,

withoutaffecting thelevel of service provided [1].Energy

effi-ciencycanbeaccomplishedinthreedifferentways:“requiringless

energytoachievethesameresult”,“requiringthesameamount

ofenergytoproducea betterresult”and“requiringlessenergy

toproduceabetterresult”.Inordertoreducetheenvironmental

impactoftheenergysector,itisnecessarytominimizethe

require-mentsofenergyandtoincreasetheenergyefficiencyandtheuse

ofrenewableenergy. Inadditiontotheenvironmentalbenefits,

theenergyefficiencyalsohassignificanteconomicand

compet-itiveness advantages, permiting to reduce the external energy

dependence.Additionally,mostoftheenergyefficiencymeasures

haveshortpaybackperiodsandultimatelyaddtobottomline

pro-fitsascontinuedincreasesinthepriceoftheenergy[2].

∗ Correspondingauthor.Tel.:+34626876673. E-mailaddresses:edwin.rodriguez@upm.es,

edwinrodriguez@bioclimaticos.com(E.Rodriguez-Ubinas).

In 2005, the European Union set out its political position

regardingtheenergyefficiencyintheGreenPaperonenergy

effi-ciency,thisdocumentestablishedthenecessityofdoingmorewith

less energy [3]. In thesame line in 2006, theEuropean Union

publisheditsstrategyforareliable,competitiveandsustainable

energy support and the action plan for energy efficiency [4,5].

Buildingsectorhasahighpotentialofimprovementintermofits

energyconsumption.Beingawareofthis,theEuropeanUnionhas

issueddirectivesinwhichitisrequiredthattheMemberStates

takesmajorstepstoincreasetheirbuildingsenergy-efficiency.In

2002,itissuedthefirstEnergyPerformanceofBuildingsDirective

(EPBD)andin2010approvedtherecastEPBD[6,7].These

direc-tivesemphasizedtheneedtoreducetheenergyrequirementsand

increasetheenergyefficiencyofbothnewandexistingbuildings.

Inthe2002EPBD,itwasincludedtheuseofrenewableenergy,but

therecastonehasgonebeyond,introducingtheneartozeroenergy

building(ZEB)concept.NeartoZEBisveryhighenergyperformance

buildingthatrequiresaverylowamountofenergy,andtheirenergy

requirementsarecoveredtoaverylargeextentbyenergycoming

fromrenewablesources.TheZEBdefinitionstates,aspre-requisite,

thatthebuildingisalowenergyone.Mostofthebuildingenergy

consumptionisrelatedwiththemaintenanceofhydrothermaland

lightingcomfort.AsshowninFig.1,alowenergybuildingneeds

firsttoreduceitsenergyrequirements,respondingadequatelyto

itsenvironmentalconditions,havinganappropriatedenvelopeand

http://dx.doi.org/10.1016/j.enbuild.2014.06.019 0378-7788/©2014ElsevierB.V.Allrightsreserved.

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Fig.1. Lowenergybuildings.

usingpassivedesignstrategies.Furthermore,highenergyefficiency

systemsandequipmentneedtobeselected.

SolarDecathlonEurope(SDE)isaninternationalcompetition

basedontheU.S.DepartmentofEnergySolarDecathlonandcreated

throughanagreementbetweentheSpanishandUnitedStates

Gov-ernment.Inthiscompetition,universitiesfromallovertheworld

arechallengedtodesign,buildandoperatesustainablezeroenergy

houses[8–11].Participatinghousesaregrid-connectedandusethe

sunastheonlysourceofrenewableenergy.Duringthecompetition

finalphase,eachteamassemblestheirhouseinMadrid,attheSolar

Village.Thefinalphaseincludeshousesexhibition,publicvisitsand

thecompetitionweeks.Aspartofthecompetition,thehouses

par-ticipateintencontests,reasonwhytheCompetitiontakesthename

ofDecathlon.SDEhasanobjectivetoimpulsetheresearch,

educa-tionandsocialawarenessinrelationtotheresponsibleuseofthe

energy,theuseofrenewableenergyaswellastheenvironment.

Sincethebeginning,followingtheobjectivesoftheEuropean

Directives,theSolarDecathlonEuropeencouragethe

participat-ingTeamstodevelopahighlyefficientsolutions.SDEhousesmust

bedesignedandequippedwithtechnologiesthatpermitthe

max-imum energy efficiency. Participating housesare challenged to

reachthelevelofzeroenergyhouses;itsperformanceintermof

functioning,theircapacityofmaintainingastrictlevelofcomfort

conditionsandtheenergyconsumptionismonitoredcontinuously,

duringtwelvedays[12].Certainly,theenergyefficiencyisakey

factoroftheSDE.Thehousesenergyefficiencywaspartofthe

Engi-neeringjuryassessment,andithadacrucialinfluenceintheresults

oftheEnergyBalance Contest.However,intheSolarDecathlon

therewasnotacontestinwhichtheenergyefficiencywas

specifi-callyassessed,notintheUnitedStatesorEurope.IntheSDE2012,

“EnergyEfficiencyContest”wasintroducedforthefirsttime.Inthis

contest,theenergyefficiencyoftheparticipatinghousesis

evalu-atedforajuryconstitutedbythreeinternationalexperts.Thisnew

contestwasaddedhavingtwoprincipalobjectives:focusstudents’

attentiononefficientsolutions,andraisepublicawarenessabout

thesignificanceoftheenergyefficiency.Inthispaperthe

evalua-tionoftheenergyefficiencyofzeroenergybuildingsisanalyzed,

usingtheSDE2012housesascasestudiesandhavingthefollowing

mainobjectives:

• Presentpassiveandactivestrategiesandsolutionsusedbythe

houses,toobtainahighenergyefficiencylevel.

• Explainthe energy efficient jury base of assessment and the

results.

• Comparethejuryevaluationwiththeresultsofthemonitoring

atthecompetitionfinalphase.

Additionally,ananalysisrelatedtothezeroenergybuildings

possibilitieshasbeenalsoincluded.Adoubleanalysiswascarried

out:one,usingthemonitoredresultsofconsumptionand

produc-tioninthecompetitionand anotherusingthepredictedannual

consumptionandproduction.

Sincetheenergyefficiencyisdirectlyrelatedtothehouses

com-fortconditionsand theirfunctioning,forthis work,it hasbeen

selectedthefifteenSDE2012housesthatobtainedatleasta70%

ofthepointsin theComfortConditionsand HouseFunctioning

contests.Threehousesdidnotcomplywiththesecriteria.These

houseswerenotfinishedintheSDE shortassembletime.They

werenot ableto enter inthe competitionfromthe beginning;

someoftheirsystemwerenotcompletesetupordidnotfunction

correctly.

The present studyhasbeen organized asfollows: Section 2

presentstheenergyefficiencyinthecontextoftheSolarDecathlon

Europe.InSection3,theparticipatinghouseshighefficient

solu-tionsareexplained.Housesperformanceduringthecompetitionis

presentedinSection4.Section5focusesontheEnergyEfficiency

Jury evaluation. Comparative study between energy efficiency

assessmentandhouses’performanceinotherrelatedcontestis

pre-sentedinSection6.Finally,conclusionsareexpoundedinSection

7.

2. EnergyefficiencyinthecontextoftheSolarDecathlon Europe

2.1. SolarDecathlonEuropecontests

InSolarDecathlonEurope(SDE)therearesomeaspectsthat

arenot evaluatedin theDOESolar Decathlon.Also, in theSDE

there was an evolution between the contests of the 2010 and

2012 competitions. SDE 2012 consists of 10 separately scored

contests:Architecture,EngineeringandConstruction,Energy

Effi-ciency, EnergyBalance,Comfort Conditions,HouseFunctioning,

CommunicationandSocialAwareness,Industrializationand

Mar-ketviability,SustainabilityandInnovation.Thereareprizesforeach

ofthesecategoriesandtheteamwiththehighesttotalpointsatthe

endofthecompetitionwinsthecompetition.

Threecontests,EnergyBalance,ComfortConditionsandHouse

Functioning,consistofseveralsub-contestsanddifferent

assess-mentcriteria.Thesecontestsassessmentisbasedonthehouses’

monitoredperformance and the competition tasks completion.

Duringthewholecompletion,anSDEorganizer,calledObserver,

isineachhousetakingnoteoftheresultsofthetaskscarriedout

andobservingthattheteamscompetefollowingtheSDErules.For

themonitoredsub-contests,theSDE2012organizationdeveloped

aninstrumentationanddatacollectionsystem.Thissystem

per-mitstoknowtheperformanceofthehousesinrealtime.Allthe

dataobtainedbytheSDE2012monitoringsystemisfreelyshared

intheSDEWeb(www.sdeurope.org).Thedatacollection,scoring

andvisualizationsystemswerecustomdesignedfortheSDE2012

bytheTechnicalUniversityofMadrid(UPM)[12].Thedata

collec-torsystemmanagesthedatafromthepowermetersandallthe

housessensorsthatareconnectedtoaProgrammableLogic

Con-troller(PLC).Thissystemhasthreemainmodules:controlmodule,

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The otherseven contests are juriedcontest. Six juries, each

onecomposedbythree internationalexperts,evaluateone

par-ticularaspectof thehouse plus theinnovationin theirareaof

evaluation.Fortheinnovationpunctuation,theassessmentofall

sixjuries istaken intoaccount.Juries usetheirexperienceand

knowledgeintheevaluationofthehouses,followingthe

guide-linesdevelopedbytheSDEOrganization.Thisevaluationhasfour

phases: documentationreview, on-site evaluation, deliberation

andscoringjustification.Thedocumentationreviewgivestothe

juriestheopportunitytostudytheprojectsand tobeprepared

fortheon-siteevaluation.Jurieshaveachancetoverifythe

pro-posedsolutionsduringtheirvisitstothehouses.Alsoduringthe

housesvisits,thestudentsgivethemexplanationsandanswertheir

questions[10].

2.2. EnergyEfficiencyContest

Energyefficiencyisoneofthejuriedcontests.Theobjectiveof

thiscontestistoencouragetherightdecisionsintermofhouse

design,servicesequipmentandappliances,inordertomaintainthe

interiorcomfortandthefunctionofthehouseswiththeminimum

useofenergy.AswasexplainedinSection1,lowenergybuildings

approachstartwiththedesignsolutionsthatminimizetheenergy

demand,andalsoincludetherightselectionofactivesystemsand

equipment(seeFig.1).TheEnergyEfficiencyjurybasesits

eval-uationonthestudyofthehouses’documentation(constructions

drawingsandprojectmanual)aswellasthevisitofthehousesand

theteamsexplanations.

Thedocumentationof housesincludescomplete information

aboutthehousesmaterials,strategiesandsystems;italsoincludes

annualthermalandenergyanalysis.Teamscarriedouttwo

differ-entthermalandenergysimulations:oneusingtheirlocalcontext

conditionsandanotherwiththemonitoredperiodconditions.The

monitoredperiodsimulationsfortheSDE2012tookintoaccount

theenvironmentalconditionsofMadridandtherequirementsof

thecompetition.Theseanalysisandsimulationshelptheteamto

bepreparedforthecompetitionfinalphase.Ontheotherhand,the

analysisandsimulationsintheirlocalcontextareusedforthejury

toevaluatethehousesenergyefficiencyinthehousepermanent

location.

The SDE organization ask the jury to evaluate the energy

efficiencyinthehouses,focus onthehouse’senvelope,passive

or mostly passive systems, active systems (HVAC,lighting and

hotwater),energy analysisandestimatedannual consumption,

appliancesselection, andcontrol systems.In energy analysisof

the house, thejury looks for the effective communication and

synthesis of the team’s design decisions and analysis process,

aswellasthe correctapplication ofengineering principlesand

how the simulations influence the improvement of the

defini-tivehousedesign.Additionally,innovativesolutionsareassessed

positively.

2.3. RelationbetweentheenergyefficiencyandotherSDE2012

contests

ThetenSDE contestsand thewaytobeassessedareclearly

definedintheSED2012Rules[10].Mostofthesecontestsare

inter-related.EnergyEfficiencyContestisrelatedwithotherjuriedand

monitoredcontests.Theserelatedcontestswereusedaspartofthe

comparativestudybetweenEnergyEfficiencyJuryassessmentand

houses’performance,seeSection6.

Energy efficiency is mostly related with the three juried

contests:Architecture,EngineeringandConstructionand

Sustaina-bility.AsfortheEnergyEfficiencyJury,SDErulesrequiredthatthe

ArchitecturalJurytakeintoaccountaspectsasthepassivedesign

strategies.TheEngineerJurymustincludeintheirevaluationthe

houseenvelopeaswellasthesystemsselected(hotwater,

light-ing,etc.).Finally,theSustainabilityJuryassesstheaspectsrelated

tothebioclimaticsolutionsandenergyissues.

Furthermore, the energy consumption of houses is mainly

relatedtotwopurposes:tomaintaintheinteriorcomfort

condi-tionsandkeepthehousefunctioning.Anenergyefficiencyhouse

mustfulfilltheseobjectiveswithminimumenergyconsumption.

IntheSDE2012,thethreemonitoredcontestarerelatedwiththe

followingobjectives:ComfortConditions,HouseFunctioningand

EnergyBalance.SincetheSDEhousesareall-electricalhouses,the

contestiscalled“ElectricalEnergyBalance”.Fig.2showsthe

sub-contestsincludedineachoneofthem.Inthenextsections,this

contestwillbeexplained,andareasrelatedwiththehousesenergy

efficiencywillbehighlighted.

2.3.1. ComfortConditionsContest

Theobjectiveofthiscontestistoassessthecapacitytoprovide

andmaintaininteriorcomfortconditions.AsshowninFig.2,the

ComfortConditionsContestincludesseveralsub-tests,butforthis

analysisonlythosewhichmayrequiretheconsumptionofenergy

wereused:interiortemperatures,relativehumidity,airqualityand

thelighting level.Fromthis point on, theterms“Interior

Com-fort”and“ComfortConditions”,donotincludetheAirborneSound

Insulationtestresults.

Drybulbtemperaturesensorsmeasureconstantlytheinterior

temperature.Thereweretwotemperaturesensorsineachhouse,

installedinpolesat150cmfromthefishingfloorlevel.These

sen-sorswereplacedatthecenterofthelivingareasandbedrooms.

The SDE 2012 monitoringperiod was fromSeptember 17th to

September28th.SDEstatesthattheteamsearnpointswhenthe

interiortemperatureisbetween20and28◦C,obtainingthe

max-imumpunctuationinmeasurementbetween23andto25◦C,as

showninFig.3a.Humiditysensorswerelocatednexttothe

temper-atureones,andtherelativehumiditywasalsoconstantlymeasured.

Themaximumpunctuationisobtainedmaintainingthehumidity

levelsbetween40%and55%.TheFig.3bshowstherelativehumidity

sub-contestpointsdistribution.

AnCO2 sensoris locatedin atripodatthecenterofthe

liv-ingarea,permittingcontinuousmonitoringoftheairquality.All

availablepointsareearnedbykeepingthecontentinCO2below

800ppm,andreducedpointsareearnedifthecontentinCO2 is

between800ppmand1200ppm.Therewasalsoaluminancemeter

placedinthehouseworkplace.Allavailablepointsareearnedatthe

conclusionofeachscoredperiodbykeepingthelightinglevelabove

500luxduringthescoredperiod.Reducedpointsareearnedifthe

lightinglevelisbetween300luxand500lux.Reducedpointvalues

arescaledlinearly.

ForthefirsttimeinSDE,duringthe2012competition,there

wasasingularperiodof56continuoushours,called“Passive

Mon-itoredPeriod”.Duringthisperiod,nothingintermsofmonitoringor

punctuationschange,buttheTeamscanuseonlypassivesystems

orstrategiestomaintaintheinteriorcomfort.Forthepurposesof

theSDE,“passive”meansanystrategyorsystemthatnotrelying

isthefunctionona“thermodynamiccycle”ordevicesthatdonot

haveaninternalproductionofheatorcold.Semi-passiveorhybrid

systemsthatusedsmallpumpsandfanswerepermitted.However,

theuseofelectricalheaters,chillers(airconditioner),heatpumps

orotherequipmentthatincludeathermodynamiccyclewasnot

allowedduringthisperiod.

2.3.2. HouseFunctioningContest

Inthiscontest,thefunctioningofthehousesandtheir

appli-ancesare evaluated.Asshownin Fig.2,theHouseFunctioning

Contest hastensub contests. Thissub-contesttriestosimulate

thedemandingstandardsofpresentdaysociety,reproducingthe

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Fig.2.SDEcontestsevaluatedbycontinuousmonitoring,punctualmeasurementsandtaskscompletion.

pointscompletingthetasksasindicatedintheCompetition

Cal-endar,andcompliedwiththerequirementsstatedintheSDE2012

Rules.Theselectionofhighefficiencyequipmentandappliances,

andusethemcorrectlyduringthecompetition,helpTeamstoget

highscoresinbothHouseFunctioningandElectricalEnergyBalance

contests.ctly,helptheteamstogetpointsintheHouseFunctioning

contest,andalsointheElectricalEnergyBalance.

3. Participanthousessolutionstogetahighenergy efficiencyperformance

Energyefficientbuildingsareabletomaintaintheinterior

com-fort and provide the necessaryservices with minimum energy

use, in a cost-effective and environmentally sensitive manner

[13]. In order to achieve that, it is fundamental to select the

rightbuildingenvelope,useappropriatedpassivestrategies and

toinstallhighefficientactiveconditioningsystems,lightingand

otherrequiredequipment.Thecorrectselectionofstrategies,

sys-temsandequipmentstartwiththecompleteunderstandingofthe

localenvironmentalconditions.

However,SDEisaninternationalcompetition.IntheSDE2012,

teamsparticipated fromall over thewhole world. Therewere

housesfrommanyEuropeancountriesaswellasfromAsiaand

South America. Thehouses came fromlatitudes between55.7◦

Northand22.5◦South.

ThispointouttooneofthechallengesoftheOrganizerofthe

Competition,howevaluatehousesfromverydifferentlocal

con-ditions.Inordertoassessthehousesperformanceintheirlocal

contextSDEOrganizationlookforinternationalexperts.

Inorder togetgood results, alsoin themonitoredcontests,

teamsstudiedtheenvironmentalconditionsofthecompetitionsite

andmadeadjustmentstotheirhousesaccordingly.Someofthem

clearlyexplain,in theirdocumentation, thesolutionsorsystem

addedtothehouse,inordertorespondadequatelytothe

comple-tionconditions.Inthenextsection,solutionsadequatetoMadrid

areexplained.

3.1. Adequatesolutionsforthecompetitionon-siteevaluation

TheperformanceofSDE2012houseswasevaluatedinMadrid.

Thiscityis locatedinthe40.24◦Nlatitudeat thecenterofthe

IberianPeninsula.Madridisat667mabovesealevel.Ithas

con-tinentalmediterraneanclimate,characterizedbycoldwintersand

hotsummers.Dryair,clearskies,highsolarradiationandhigh

diur-nalthermalswingsarecommoncharacteristicsofitsclimate.Itis

ahighpeninsula.

CIBSEinoneofitsguidestatesasprinciplesforenergyefficiency

tokeepenergydemandtoaminimumthroughcarefuldesignof

builtformandservicesusingrenewableenergysources,ambient

energyandpassivesolutions[13].Inthefollowingparagraphs,the

passivesolutionsandtheparticipatingteams’effortstotake

advan-tageoftheambientenergyandtoreducethenecessityofactive

systemsareexplained,centeredinthosesolutionssuitableforthe

Madridenvironmentalconditions.

3.1.1. SDE2012houses’envelopeandpassivestrategies

SDE 2012teams,ingeneral,selectedvery highperformance

envelope[14].Additionallymostofthemworktoprovidean

air-tightconstruction.Fig.4shows thewallsandwindowsthermal

transmittance(Uvalue)ofthefifteenhousesofthisstudy,aswell

astheirglazingSolarHeatGainFactor(gvalue).

Inadditiontothehouseenvelopes,thereareotherstrategies

toaccomplishahighenergyefficiencyperformance.Parasonis[15]

notedthatmanipulationoftheformofbuildingaltersitsenergy

usevalue,eventhoughthephysicalcharacteristicsoftheenvelopes

remainunchanged.Healsonotedthatarchitecturalsolutionsand

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Fig.4.Wallsandwindowsthermaltransmittanceandglazingsolarfactor[14].

Fig.5. Madrid:strategiesforheatingandcoolingperiods(potentialnumberofhours thatmightbeaddedtothehydrothermalcomfort).

thevolumeofabuildingcanbeusedtoachievegreaterenergy

effi-ciencyfortheentirelifecycleofthebuilding[16].Theseideasare

commentedbyGivonimanyyearsago,inrelationtothepassive

systemorsolutions.Theabilityofabuildingtosaveenergy,aside

fromitsenvelopematerials,dependsonitsshape,orientation,

lay-outoftransparentenvelopes,size,measuresofprotectionfromthe

sun,andthefacadecolor[17].

In locations as Madrid, it is needed to develop appropriate

strategiesforbothheatingandthecoolingperiods.A

psychomet-ricanalysisbringsaroughestimationonthepotentialimpactof

theuseofpassiveorhybridsolutions.ClimateConsultantsoftware

permitstorankthestrategiesusingthenumberofhoursthatcan

potentiallybeaddedtothecomfort[18].Thesenumberofhours

representjustestimation;thefinalresultwilldependonbuilding

design,andhowthesuggestedsolutionsareimplemented.

How-ever,this toolhelpstoidentifytheappropriatedstrategiesfora

specificlocation.Fig.5showstheresultsofthepsychometric

anal-ysiscarriedout byRodriguez-Ubinas etal.[19]forMadridCity,

usingthecomfortmodeldefinedinthe2005ASHRAEHandbook

ofFundamentals.Theheatingandcoolingperiodsarepresented

intworadarfigures,indicatingthepotentialofhourthatmight

beaddedtothecomfort.Forheatingperiods,internalgains,high

thermal massand direct solar gainswerethe principalpassive

strategies. And forthe coolingperiods,in addition tothesolar

protection,evaporativecooling,highthermalmass,thermalmass

withnightventilationandfanforceventilationweretheidentified

strategies.

Table1summarizesthepassive, hybridandactive solutions

usedbytheSDE2012houses.Thestrategiesdetectedinthe

psy-chometricanalysisarepresentinmostofthehouses.Thepassive

strategiesutilizedarethebaseforthehighefficiencyperformance

ofmostofthehouses.AdetailedstudyabouttheSDE2012houses

wascarriedoutbyRodriguez-Ubinasetal.[14].

It’shighradiationpointsouttheopportunitytotake

advan-tage of the direct and indirect solar gains in heating periods,

andprovideadequatesolarprotectionsduringthecoolingones.

Madrid’saltitudes,anditsdryclimate,provokehighdiurnal

tem-peratureswingsthataremoresignificantduringsummer.Thehigh

dailythermal swing enablesthe useofthermal energy storage

(TES).TheuseofthermalmassandotherTEShelpstosmoothen

theinterior temperature,andpermittoreducethenecessityof

mechanical conditioning.The Madrid’spsychometricanalyst,as

showninFig.5,recommendtheuseofTESforbothheatingand

coolingperiods.Fig.6a–dshowsthenumberofhousesusingTES.

Seventeenoftheeighteenparticipatinghousesusesomekindof

TESapplication.SomeofthemhaveSensibleTESsystemsbased

onheavymaterialsasconcrete,stoneorsandwhileothersused

LatentTESsystemstakingadvanceofthethermalstoragecapacity

ofphasechangematerials(PCM).FromtheSD2005in

Washing-ton,many SolarDecathlon houseshad usedLatentTESsystems

[20].In2012,61%ofthehousesusedthePCMpassiveoractive

applications.

Evaporativecoolingandnightskyradiantcoolingsystemscan

beappropriatestrategiesduetheMadriddryair,andclearskies

[21].Fig.6e–hshowsthequantityofhousesthatusethesehybrid

solutions.Thisfigurealsogivesinformationaboutlowtemperature

radiantsurfacesandventilationsystemwithheatrecovery.Mostof

thehousesusedifferenttypesofheatpumps,withtwoexceptions

H13andH18,seeTable1andFig.6.Thesehousesonlyuse

pas-siveandhybridsystems.InrelationoftheDHWsystems,onlytwo

housesdonotusesolarthermalsystems.Thesehousesuseonly

heatpumpsfortheDHW.

4. SDE2012monitoredperiod

4.1. Competitionweeks’environmentalconditions

In order tounderstandtheperformance of theparticipating

housesduringtheSDE2012competitionweeks,itisnecessaryto

knowtheweatherconditionsduringthemonitoredperiod.TheSDE

2012monitoredperiodwasfrom17thto28thSeptember2012.

TheFig.7showstheclimaticconditionsofthemeasuredperiod;

thefirstsixdayshada climateconditionstypicaloftheMadrid

latesummerandlastsixdayspresentedtemperaturesofthe

begin-ningofautumntemperatures,withcloudyskies,highhumidityand

somerain.

4.2. Monitoredperiodlimitationsandvalueofthejury

assessment

SDEorganizationhasdevelopedarobustandreliable

instru-mentation, monitoring and visualization system. During the

monitoringperiod,thissystempermitstoknowthehouses

per-formanceinrelationtotheappliancesuse,comfortconditionsas

wellastheirelectricalenergyproduction,storageand

consump-tion.However,theenergyefficiencyoftheparticipatinghouses

mustnot beevaluatedtakingintoaccount onlythemonitoring

period,since:

-Thehousesaredesignedforenvironmentalconditionsthatare

differenttothecompetitionsite.Insomecases,thedifferences

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Table1

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Fig.6. Housesthermalenergystorage,hybridsolutions,activeconditioningandDHWsystems.

-Teamsmakeadjustmentsintheirhousestoimprovetheir per-formanceinthecompetitionsitebutpossiblytheirhouseshave abetterperformanceintheirlocalcontext.

-The houses are monitored only for twelve days. Within this period,itisnotpossibletodeterminewithcertaintytheannual performanceofthehouses.

-Someaspectsofthecompetitionasthepublicvisitsaffectthe per-formanceofthehouses.Forexample,theuseofthermalmasscan bedisturbedbytheneedtoopenthehouseandallowhundreds ofpeoplewhoentereveryday.

Duetothelimitationsofevaluatingthehousesbasedonthe monitoreddata,it isnecessary toobtainexperts’advice.These

expertsaretheCompetitionJuries.Inthenextsections,the assess-mentoftheEnergyEfficiencyJurywillbeanalyzed.

5. EnergyEfficiencyJuryevaluations

Inthissection,theinformationrelatedtoEnergyEfficiencyJury evaluationispresented.ThisinformationisbasedontheEnergy EfficiencyJuryEvaluationReportsandthechapteroftheSDE2012 bookwrittenbyoneofthejurymember[22].Itisimportanttopoint

outthattheEnergyEfficiencyevaluationwascarriedouttakinginto

accountofthelocalcontestaswellasthedescribedconceptforthe

aftercompetitionuse.

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Table2

Ideasextractedfromthejuryevaluationreports.

Positiveelementsfoundbythejury Aspectsthatneedtobeimprovedin

somehouses

Envelope Envelope

-Thermalenvelope.Thehighlyinsulatedopaquebuildingenvelope–vacuumthermalinsulationpanels–thermal breakelements

-TheUvalueoftheopaquewallsisa bittoohigh,sameastheamountof glass

-Glazing.Differenttriplepaneglazingisappliedinhighqualityframes–vacuuminsulation–Specialglass–Air tightness

-Concerningtheeffectivenessofthe outerskintoreducethethermalstress (highinfiltrationratesinwinter, uncomfortableairflowinsummeror uncomfortabletemperaturescausedby stackeffectventilation

-Slidingdoorscausinglarge infiltrationrates).

-Largeamountofglass

-Thelowerairtightnesscreatedby theuseofslidingwindows

Passivesystems Passivesystems

-Glasssizes,orientationsandsolarprotectiontomaximizethegainsinheatingperiodsandavoidtheoverheating incoolingperiods.

-Naturalventilationwasachieved withsomedoubts

-Ventilation,naturalventilation–naturalventilationcanbeachievedquicklyandefficiently -Norealventilationconcept. -Skyisusedforpassivecooling

Thermalstorageenergy -PCMtanksfortheheatpump

-Thermalstorageintheactivesystem(heatpump)assiststoreducethepowerpeaks -Coolingceilingwithacombinationofwaterandparaffin-waxPCM

Hybridsolutions Hybridsolutions

-Highefficiencyheatexchangerintheventilationsystem Someproposedsolutionspresent

problemsrelatedwiththeirdurability andmaintenance

-Surfaceheating/coolingsystem -Goodsolutionforforcednightventilation

-Nightcoolingoftheceilingisachievedbycirculatingwaterbetweentheexternalstorageandahybridelement cleverlydesigned,wherebytheclayroofisdischargedandavailableforthenextday.

-Heatingandcoolingwereprovidedusinginertiatanksandthermalmass. -Lowtemperaturesurfaceheating/coolingsystem

-Cleversolutionsof(e.g.evaporativeadiabaticcoolingfacade)

Activesystems Activesystem

-HighefficientHVAC -Partlynonefficientdevices

-StrategiestoincreasetheefficiencyoftheHVACsystem,includingtheuseofthermalstoragesystems -Incorrectselectionofpumpsand controlsmaycausehighconsumption -Useofactivesystembasedonorcomplementedwithsensibleandlatentthermalenergystorage

-Highefficiencyappliances,pumpsandotherequipment Hotwater

-Efficienthotwatersystems -Innovativesolarsystemsused -PVandthermalhybridsystems. Daylight

-Daylightsolutionsthatreducetheenergyconsumptionandenhancetheinteriorcomfort. Controlsystem

-Advancedbuildingautomationcontrolsystem(BACS),userfriendlyandeasyunderstanddisplayedinformation

Juriesfirstassessedthedesignstrategiestoreducetheenergy demands,andthenevaluatedtheactivesystemsselectedtoreduce theenergyconsumption.Anappropriatedbalancebetweenpassive andactivesolutionswasassessedpositively.

Thejurysaidthattheevaluationwasnotonlycenteredinthe energyaspectbutalsointhecapacityofthehousestooffera live-ablespacesinwhichallthenecessaryactivitiescanbecarriedout andahealthyandhighqualityindoorenvironment.They appreci-atetheeffortofsometeamstoproducemostpassivehouses,and theinnovativesolutionsrelatedtotheenhancementoftheinterior comfortandthereductionofenergyconsumption. Additionally, theypointedoutthattheteamshavedoneagoodcontemporary re-interpretationoftheircountryvernaculararchitectureandits passivestrategies.Oneofthejurywrote:“somedesignsareinspired bytheirlocaltraditional buildings,notareturn toheritage and tradition,butusingthemasafoundation”[22].

Inrelationwiththejuryfindings,oneofthemwrote“Teams

demonstrated an extremely high level of energy efficiency in

their house design and its technical systems, components and

materialsaswellasappliances,eachcontributingtothefinal

inte-grated value of energy efficiency of the house. Their approach

tothe HVAC systems design was thoughtful and creative with

the concept selection, sizing and resolution of the HVAC

sys-tems facilities, and evaluation and optimization of passive and

activestrategies –searchingfor themostenergy efficient

com-binations. In addition, it is important to stress, that all teams

intheirsearchforenergyefficiencydidnotneglectthebroader

requirements of the house, particularly indoor air quality and

all other aspects of the indoor environment quality” [22].

Table 2 shows some ideas related with the energy efficiency

of the participatinghouses,extracted fromthe jury evaluation

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6. EnergyEfficiencyassessmentandhouses’performance inthecompetition

GiventhecharacteristicsofSDEcompetition,theenergy

effi-ciencyshouldhaveasignificantimpactintheperformanceofthe

participatinghousesintheoverallresultsaswellasinthe

con-testthatarerelatedwiththistopic.InSection2,itwasexplained

thattheEnergyEfficiencyContestiscloselyrelatedtootherjuried

andmonitoredcontests.Inthefollowingssub-sections,

compara-tivestudiesoftheEnergyEfficiencyJuryevaluationandtheresults

inotherareasoftheSDE2013competitionareincluded.

6.1. Energyefficiencyandtheoverallresults

SDE2012EnergyEfficiencyJuryconcededthefirstfiveplaces

toeighthouses.These housesearnedbetween100and 80

per-centofpointsinthiscategory,seeFig.8.Onthefinalresults,these

houseswerealsoonthefirsteightpositions.Thehousethatgot

thefirstprizeinEnergyEfficiencyalsogotthesecondprizeinthe

competition.Similarly,thehousesthatreceivedthefirstandthird

Fig.8. HousesrankingbasedonthepointsearnedintheEnergyEfficiencyContest.

prizesweretiedinthefourthpositionoftheEnergyEfficiency

eval-uation.It can,therefore, beconcludedthat certainlytheenergy

efficiencyhouseswonthecompetition.

6.2. Energyefficiencyandotherrelatedjuriedcontests

AsexplainedinSection2,someaspectsrelatedwiththeEnergy

Efficiency have also influenced the evaluation of other juried

contestsuchas Architecture,Engineeringand Constructionand

Fig.9.Energyefficiencyresultsversusotherrelatedjuriedcontests.

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Sustainability.TheeighthousesinthefirstfivepositionsofEnergy

Efficiencywereusedtoillustratetherelationbetweenthiscontest

andotherjuriedones.AsshowninFig.9,therearegood

agree-mentbetweenEnergyEfficiencyandtheEngineeringevaluation.

Thethree firstplacesin Engineering(H11, H03andH02) were

alsointhethreefirstplacesofEnergyEfficiency.Additionally,the

samehousesareinthefirstsevenpositionsofthesebothcontests.

Therewasalsoagoodagreementbetweentheevaluationofthe

EnergyEfficiencyandSustainabilityassessment.IntheSDE2012,

fiveofthehousesthatwerebetweenthefirstandfourthposition

inEfficiencywerealsointhesevenbestplacesoftheSustainability

Contest.Similarly,thesixbesthousesinArchitectureEnergy

Effi-ciencywerealsointhefirsteightofEnergyefficiency.However,as

showninFig.9,thehousesH05andH03obtainedthesecondand

thirdpositioninEnergyEfficiencybuttheydonotgethighgrades

inArchitecture.

6.3. Energyefficiencyandothermonitoredcontest

Before starting the presentation of the comparative study

betweentheEnergyEfficiencyJuryassessmentandhouse

perfor-manceduringthemonitoredperiod,itisnecessarytoindicatethat

themeasurementresultswerenotknownatthetimeofjury

eval-uationandtohighlightthedifferencesbetweentheseevaluations.

Themonitoredevaluationgivesinformationofthehouses

perfor-manceintheenvironmentalconditionsofthemonitoredperiod.

Theseenvironmentalconditionsmightbedifferentfromthehouses

permanentconditions.Similarly,thehousesconsumptionisrelated

withthecompetitiontasksrequirements.Thefrequency,andthe

times,inwhichthesetaskswillbeperformedintheirpermanent

houselocationisdifferent.Anotherlimitationofthemonitoring

informationisthelimitedtime,twelvedays.

Ontheotherhand,aswasexplainedforoneoftheJury,they

evaluated the houses based on their expected performance in

theirpermanentlocation.Thisevaluationtakesintoaccountthe

environmentalconditionsofthehousespermanentlocation.Jury

assessmentisbasedonthedocumentationsubmittedbytheTeams

andthevisitstothehouses.Completeandprecisedocumentation

helpthejurytogetabetterunderstandingofthehouses’

strate-giesandtheirenergyperformanceintheirlocalcontext.Therefore,

teams’capacity tocommunicate theirprojectsmight affectthe

resultoftheJuryassessment.

Additionally,themonitoredperformanceisinfluencedinthe

occupant’s behavior. The occupant’s actions have a significant

impact in the buildings consumption. Fig. 10 summarizes the

resultsoftheenergy efficiencyassessment inrelationwiththe

relatedjuriedandmonitoredcontest.

6.3.1. EnergyEfficiencyJury’assessmentandComfortConditions

results

Energyefficiencyisnotinconflictwiththecomfortconditions;

onthecontraryoneofthechallengesoftheenergyefficiency

build-ingistomaintaintheinteriorcomfortusingaminimumofenergy.

Fig.11showstherelationbetweentheevaluationoftheEnergy

EfficiencyJuryandtheinteriorcomfortconditionsduringthe

mon-itoredperiod. Inthis figureonly thevalues ofdry bulbinterior

temperature,humidityandairqualityweretakenintoaccount.

TheSDE2012requirementsintermsofcomforttemperatureare

verystrictand,insomeoccasions,itisdifficultformost-passive

housestogethighpunctuation.Intheanalysisof theresults, it

wasfoundthatsixoftheeighthouseswithhigherpunctuationin

ComfortConditionswereinthefirstfifthpositionintheEnergy

Efficiency Jury. However,thefirst and second placesin Energy

EfficiencywerenotinthehouseswiththehigherpositioninThe

ComfortConditionsContest.

Fig.11.Energyefficiencyandcomfortconditions(drybulbtemperature,relative humidityandairquality).

Fig.12.Energyefficiencyandhousefunctioning.

Fig.13.Energyefficiencyandelectricalenergyconsumptionpersquaremeter (dur-ingthewholemonitoringperiod).

6.4. EnergyEfficiencyandHouseFunctioningContestsresults

InSection2.3.2,theHouseFunctioningContestswasexplained.

Everydayteammembershavetoperformalltherequiredtasks

following the competition calendar. Fig. 12 shows therelation

between the EnergyEfficiency Jury assessment and the House

FunctioningContestresults.Asshowninthisfigure,thereareno

correlationbetweentheEnergyEfficiencyJuryandtheHouse

Func-tioningresults.

6.5. EnergyEfficiencyJury’assessmentandconsumptionperm2

results

The final objective of theenergy efficiency is to reducethe

energyconsumption.Inthecompetition,theconsumptionofthe

housesismonitoredcontinuouslyandatthefinalthis

consump-tionisrelatedwiththenetareaofthehouse.Thehousewithless

consumptionwinstheEnergyConsumptionperm2Contest.Fig.13

showstherelationbetweentheEnergyEfficiencyJuryassessment

andtheenergyconsumptionduringthemonitoredperiod.Aswas

previouslyclarified,theconsumption during thecompetitionis

relatedwiththeenvironmentalconditionsofthemonitoringperiod

andthetasksrequiredinthecompetitioncalendar.Thevalueof

thiscontestisnotdirectlyrelatedwiththerealconsumptionofthe

housesintheirpermanentlocation.

H02,H06,H16andH05obtainthefourbestpositionsonthe

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Fig.14.Energyconsumptionversusenergyproduction(duringthemonitoredperiod).

lessenergyconsumptionduringthecompetition.However,most

ofthesehouseswerenotatthetopplacesofothermonitored

con-tests.TheexceptionwasH16,whichobtainedaremarkablygood

positioninallthreemonitoredcontestsrelatedtoenergyefficiency.

Thishousehadalow-energyconsumption(thefourthlowest),and

wonthefirstplaceinHouseFunctioning.Italsowonthethirdprize

inInteriorComfort.

Moreover,theEnergyEfficiencyJuryassignedtoH15theeighth

positionbehindthefirstelevenhouses.However,thishousehada

goodperformanceinthemonitoredcontests,firstplaceinInterior

Comfort,thirdinFunctioningHouseandeighthinConsumption

perMeasurableArea,consuminglessthanfourofthehousesmost

valuedbythejuryofenergyefficiency.

6.6. Energyefficiencyassessmentsandtheenergyzerobuilding

challenge

Certainlytobeanenergyefficientbuilding,itisnotneededto

generateenergy.Energyefficiencyismostlyrelatedtothe

reduc-tionoftheenergyconsumption.However,thefirstrequirement

statedbytherecapEPBDistobehighefficientbuilding,andbeing

thecasestudiessolarhouses,itisfundamentaltoknowifthese

housesqualifytobecalledzeroenergybuildings.Thisanalysiswas

carriedoutintwodifferentscenarios:energybalanceon-site

(dur-ingthemonitoredperiod)andpredictedannualenergybalance.

TheSDEhousesareall-electricbuildings.Thissimplifiestheenergy

balanceequationsinceitisnotneededweightingfactorsforthe

calculation;electricityistheonlyenergysuppliedanddemanded.

Forthisreason,thecontestrelatedwithmonitoredenergy

perfor-manceiscalledelectricalenergybalance.

6.6.1. Electricalenergybalanceduringthemonitoredperiod

Theenergyconsumptionofthehousesduringthetwelvedays

ofthecompetitionwasgreaterthantheirregularconsumption,

sincethecompetitionrequiredanintensiveuseofhotwaterand

appliances(suchasovens, washingmachinesanddishwashers).

Evenso,thefifteenhousesanalyzedhadapositivebalanceduring

thecompetitionperiod asshown inFig. 14a. Duringthe

moni-toredperiod,theaverageconsumptionofthehouseswas146Wh,

beingthehighestconsumption198Wh.Intermsofenergy

produc-tion,theaverageelectricalenergyproductionwas208Wh,andthe

highestproductionwas421Wh[14].DotsintheFig.14b

repre-senttheenergyrequiredforthehouses,thedashedlinerepresents

theenergythatwasproducedbythehousewiththesmallestPV

installationandthecontinuouslinerepresenttheaverageofenergy

thatwasproducedbythehouses.Thisfigureshowsthat,inthe

hypotheticalcaseinwhichtheelectricalenergygenerationofall

thehouseswouldhavebeenequaltothelowestone,mostofthem

wouldcontinuehavingapositivebalanceduringthecompetition

period.

Fig.14showstheresultofthecomparativestudyoftheenergy

consumptionofthesehouseswiththeproductionofthesmaller

PVarraypresentedintheSDE2012,aswellaswiththeaverage

productionduringthemonitoringperiod.

6.6.2. Predictedannualelectricalenergybalance

Themonitoredperiodarenotenoughtodeterminingtheenergy

performanceofthehousesortheirenergybalance.

Fortheannualenergyanalysis,theenergysimulationcarried

outbytheparticipatingteamswasused.Theresultsofthese

sim-ulationsprovideanannualestimationofhousesenergydemand

andgeneration.AsFig.15ashows,allthestudiedhousesqualify

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tobeclassifiedasPlusEnergyBuildings,providedthattheirfinal

energybalancecoincideswiththeestimatedvalues.Indeed,being

grid-connectedhouses,theycouldbeclassifiedasNetPlusEnergy

Buildings[23,24].Anadditionalhypotheticalpossibilitywasalso

analyzed.DoallthehousesbeEnergyPlusBuildingshavingthe

samesmallenergygenerationasthehousewiththesmallerPV

array?AsshowninFig.15b,allthefifteenhousescontinuebeing

NetPlusEnergyBuildings. Thisispossiblesince allthestudied

housesarelowenergybuildings.

6.7. Recommendationsforfuturecompetitions(howthis

recommendationaffecttheenergyefficiencyassessment)

Whilethisresearchwascarriedout,itwasfoundsomeelements

intheSDE2012competitionthatneedtobere-thought.Someof

themarerelatedwiththepossibilitiestoenhancetheuseofpassive

andhybridsolutions;othersarerelatedwithgetabetteranalysis

ofthehousesenergyperformance.

Recommendationregardingpassiveandhybridsystems:

-Takeintoaccounttheradianttemperature,evaluatingthe

oper-ativetemperatureandnotonlytheairtemperature.

-When the competition is held during the summer, used the

adaptivecomfortinstateoffixedcomfortbands,Additionally,

evaluatedthepossibilitytohaveadifferentcriteriatoevaluate

thetemperatureduringthenights,usingalowertemperaturein

theassignationofpointsandavoidingpenalizingtheuseofnight

ventilation.

Recommendationsregardinghousesenergyperformance:

-Installadditional powermeterstomonitorindependentlythe

HVAC/DHWconsumption.These meterswillregisterthe

con-sumptionrelatedwiththehouseconditioninginbothpassiveand

regularmonitoredperiods.

-Determinatetheenergyconsumptioninthelocalcontextofthe

houses(totaland relatedwithHVAC/DHW),inordertoverify

theirimprovementinenergyefficiency.

-Limittheenergyconsumptionofthehybridsystemsduringthe

passivemonitoredperiod.Inthisperiod,itisalsoneededthat

interiorlightinglevelsbeingmonitored.Itisfundamentalthat

thehousesgetacorrectbalancebetweenthesunprotectionand

thedaylightpossibilities.

7. Conclusions

Energyefficiencybuildings are characterizedby a good

bal-ancebetweenpassivestrategies(meanstominimizetheenergy

demand), and high efficiency equipment(means of reduce the

consumption).ThegoalsofthefirstEnergyPerformanceof

Build-ings Directive (EPBD) are closely related with these very low

energy buildings. Also, the goals of the recast EPBP in

rela-tiontoneartozeroenergy buildingsare basedonthis kindof

buildings.

In this paper, fifteen houses that participated in the Solar

Decathlon Europe2012 (SDE 2012) were used as case studies.

The SDE has been successful in extending the understanding

of sustainable construction and the importance of passive and

solardesign strategies touniversitystudents, professionals and

thegeneralpublic.Itsrulesemphasizedthereductionofenergy

consumption in buildings, the increment of energy efficiency

in buildings and the need to cover the energy demanded to

a very significant extent with energy from renewable sources

producedon-site.

The studied houses include many passive design strategies

aswellasenergy efficiencysystemsandequipment.Thispaper

includesareviewofthesesolutions.Italsoincludesacomparative

studybetweentheEnergyEfficiencyJuryevaluationandthe

mea-suredperformanceofthesehousesinthecompetition.Manyof

thehousesachievedanexcellentbalancebetweenpassive

strate-gies(envelope, orientation,heating and cooling strategies) and

highefficiencyactivesystems.Thesedesigndecisionshelpthemto

maintainhouseshydrothermalcomfortanddoallhousesregular

taskswithminimumenergyconsumption.Thislowconsumption

permitsthatallofthemobtainedapositiveenergybalanceinboth

intheannualenergysimulationsandon-siteduringthemonitored

period.Iftheirenergyperformance,onceplacedintheirpermanent

location,issimilartothepredictedone,allofthemwillqualifyto

bePlusNetEnergyBuildings.

Additionally,somerecommendationsthatcanhelptogeta

bet-ter understandingof the participatinghousesenergy efficiency

wereidentified. In relationwiththecomfort conditions, it was

recommendedtotakeintoaccounttheradianttemperature,

evalu-atingtheoperativetemperatureandnotonlytheairtemperature.

Inthesummer,competitionusedtheadaptivecomfortinstateof

fixedcomfortbands,andpermitsthelowertemperaturesinthe

nighthourstodonotpenalizetheuseofnightventilation.Related

withenergyconsumption, a powermeterneedstobeinstalled

inordertomonitorindependentlytheHVACconsumption.Also,

shouldbegoodtohavereferencesabouttheenergyconsumption

(totaland inHVAC)intheparticipatinghouseslocalcontextin

ordertoverifytheirimprovementinenergyefficiency.Finally,for

thepassivemonitoredperiod,theconsumptionofthehybrid

sys-temsshouldbelimited,andthelightinglevelduringthisperiodis

monitoredcontinuously.

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