Thermal Mass & Insulation: Domestic Buildings in the Mediterranean Climate

Architectural Association School of Architecture | Graduate SchoolAA SED MSc + MArch Sustainable Environmental Design 2014 - 2015 | Research Paper 1 | January 2015

THERMAL MASS AND INSULATION: DOMESTIC BUILDINGS IN THE MEDITERRANEAN CLIMATE

Olga Tsagkalidou

Thermal Mass & Insulation: Domestic Buildings in the Mediterranean Climate

AUTHORSHIP DECLARATION FORM

Research Paper 1

TITLE: Thermal Mass and Insulation: Domestic Buildings in the Mediterranean Climate

NUMBER OF WORDS: 3367

STUDENT NAME: Olga Tsagkalidou

DECLARATION: “I certify that the contents of this document are entirely my own work and that any quotation or paraphrase from the published or unpublished work of others is duly acknowl-edged.”

Signature:

Date: 16 January 2015

02Architectural Association School of Architecture Research Paper 1 | MSc + MArch Sustainable Environmental Design 2014 - 2015


TABLE OF CONTENTS

Abstract1. Introduction2. Climate Analysis3. Domestic Buildings in Greece 3.1.Classificationoftheresidentialbuildingstock 3.2. Construction and characteristics of domestic buildings4. Thermal Mass and Insulation5. Precedent Studies 5.1. Recommendations of the EPCs 5.2.MeasuresforefficientenergysavingandCO2 reduction6.ConclusionsAcknowledgementsReferences



ABSTRACTThe latest worldwide trend to reduce the carbon footprint puts European Union in the road of setting new energy ef-ficiencytargetsforitsMemberStates.InGreecetherecentlyadoptedlegislationhastriggeredarenovationplanofthenational building stock. This paper examines the characteristics of the domestic building stock, highlighting the existent thermalmassstructureandthelackofthermalinsulation.Finally,theeffectivenessofthecurrentlyproposedmeasuresandofalternativeonesthatfocusontheimprovementofthebuildingenvelope’senergyperformance,isalsoanalyzed.

Keywords:energyefficiency,domesticbuildings,mediterraneanclimate,buildingfabric,thermalmass,insulation,En-ergyPerformanceCertificate,legislation,buildingstock,night-ventilation,renovationmeasures

Under the pressure of the forthcoming climate change and the urgent necessity for smart and sustainable growth and energy security, policy makers in the European Commissionhaveestablishedasetofgoalsregardingen-ergyefficiencymeasurestobeachievedfromtheMemberStatesby2020.ThepurposeoftheEurope2020Strategyis to create 20% of the energy consumption from renew-ableenergysources(RES)andincreaseenergyefficiencyby 20%. The building sector is going to play a paramount role in the outcome of the desired result. The existing building stock in European countries constitute over the40%offinalenergyconsumption,ofwhichthe63%comesfromtheresidentialbuildingstock(Balarasetal,2005). The status quo of the domestic building sector in Greece is identical,accounting for the24%of thecoun-try’s total energy consumption. In order to alleviate theCO2emissionsandmeettheEU2020targets,theGreekState adopted in 2008 the European Directive 2002/91/ECfortheEnergyPerformanceofBuildings(EPBD).Theschemeisinusesince2010,incorporatingacertificationprocess, throughwhichEnergyPerformanceCertificates(EPCs)areissued.Theprocessfirstlyaimstocategorizethe performance of buildings to energy classes and sec-ondly to propose recommendations for improvement incase thebuilding isclassified inclassBor lower (Gele-genisetal,2013). Having in mind the Greek residential buildingstock, its constructional characteristics and its building envelope’spoorperformance,aswellastheunpromisingoutcomesofrecentstudiescarriedoutregardingtheeffi-ciencyoftherecentlyissuedEPCs(Gelegenisetal,2013),aconcernremainsonwhetherGreeceisontherightsideoftheroadtowardsachievingthe20%carbonemissions’reduction or would fall short of the targets for 2020 set by the European Union.

1. INTRODUCTION

04

In generalGreecehasaMediterranean climate.Inorder tocaptureamorespecific rangeof theclimate,weatherdatafromtwodifferentcities,Athens(Lat.37.967)and Thessaloniki (Lat. 40.517) are presented (Figures01 and 02).The annual cycle can be divided into threeseasons,summer(June–August),amid-season(March–May&September–October)andwinter(November–February). Lower temperatures occur during the winterseason reaching -7°C in Thessaloniki located in North-

2. CLIMATE ANALYSIS

ernGreece,whereastemperaturesinthesummerperiodcouldrisehigherthan36°Cinbothcities.Itisobviousthatenergy conservationmeasures should take into accountthe cold winters as well as hot summers that could lead in overheating risks.Temperatures differences during eachmonthcanexceed10°K,givingan indicationofpossiblepassivecoolingstrategies,especiallyduringthesummerperiod.

Figure 01: Monthly Temperature of Athens (Source: Meteonorm)

Figure 02: Monthly Temperature of Thessaloniki (Source: Meteonorm)

According to theTechnicalGuidelines issuedbytheTechnicalChamberofGreeceandusedfortheEPCsassessment(TOTEE20701-1/2010),theGreeklandscapeisdivided into fourdifferentclimaticzonesbasedon thelatitude, local climate and altitude of each county (Figure 03).This classification is important because it gives theenergy performance standards according to which the building’senergyclassiscalculated.

3.1. Classification of the residential building stock

3. DOMESTIC BUILDINGS IN GREECE

Recent studies have focused on categorizing -based on age and usage criteria - the existing urban build-ingstockinGreece,sinceidentifyingavastfieldofinter-estinrelationtopromotingenergyconservationandCO2emissionsreduction(Figures04and05).Inparticular,do-mestic buildings constitute the 75% of the total building stockinGreeceandareresponsibleforthe73.6%oftheenergy consumed by the whole building sector (Balaras et

Architectural Association School of Architecture Research Paper 1 | MSc + MArch Sustainable Environmental Design 2014 - 2015


Figure 03: Climatic Zones of Greece (Source: Technical Chamber of Greece - T.O.T.E.E. 20701-1/2010)

al,2005). Basedonatypology-usageclassification,residen-tial buildings constitute the majority of the building stock of theGreekcities, reachingapercentageof79%.Usu-allytheresidentialbuildingsinGreecearemono-functionalmulti-storeyapartmentblocks(Figures06and07),whatisalso known with the term “Poly-katoikia” (translated from Greek:many-dwelling)(Theodoridouetal,2011). The classification of the building stock accord-ingtotheageoftheirconstructionisvaluablebecauseitgives indicationsabout the constructional characteristicsof the buildings. Figure 04 represents the percentage of residential buildings for different periods of construction. Theyear1979couldbeconsideredasapivotalmomentintheconstructionfield,duetotheenactmentoftheTher-malInsulationRegulation(TIR).Accordingtoamorede-tailed study which was based on statistical data from the HellenicStatisticalauthority(Theodoridouetal,2011),thebuildingsbuilt inurbanareasofGreecebefore1980are1,496,102 corresponding to the 74.6% the total buildingstock,whereastheonesbuiltafter1980areonly507,712.Consequently, it isevident that themajorityof theexist-ing building stock is uninsulated, representing a low quality building fabricandgiving indicationsofpoorenergyper-formance. Higher insulation standards were adopted by Greekpolicymakersonlysince2010withtheapplicationoftheEuropeanDirective2002/91/ECtoallnewbuildingpermits.However,duetoeconomicandpoliticalreasonsand theeconomiccrisisof2008,a largedrop inpermitshasbeenobservedfornewlyconstructedbuildingssince2007(Theodoridouetal,2011),makingtheproblemoflowquality building stock more intense.

Figure 04: Breakdown of Hellenic building stock for different periods of construction (Source: Balaras et al, 2005)

Figure 05: Breakdown of Hellenic building stock according to the end use ofthebuildingsfor1990(Source: Balaras et al, 2005)

3.2. Construction and characteristics of domestic buildings

Thestrongseismogenicactivity that takesplacequiteofteninGreeceisoneoftheenvironmentalfactorsthat has an impact on the building construction. In order tofollowtheseismicregulations,buildingsshouldhaveaverystrongbearingstructure.Asstatedinarecentworks(Papamanolis, 2004; Theodoridou et al, 2011), focusingon the analysis of the constructional characteristics of do-mestic buildings, the bearing structure of most of the build-ingsinGreeceisofreinforcedconcrete.Inrelationwiththestrictstandardsobligedby theGreekSeismicCode, theresult is constructions of high thermal mass. Ceramic bricks and plaster are the main materi-als used in the construction of walls. The external walls usuallyconsistofdoublerowsofbricks9cmthickwithaminimum7cmcavitybetweenthem.Incontemporarycon-structionsthiscavityiffilledwitha5cminsulationboards,usuallyextrudedpolystyreneinsulation(EPS)orexpand-edpolystyrene(XPS).Alayerof2mmofplasterisusuallyappliedonboth sidesof thewall, resulting in anoverallthickness of 25 – 30 cm. Internal walls within apartments consistofasingle9cmbrickrow.AnEPSorXPSlayer,usually around 3 mm, is used onto the external surface of thebearingstructure(Papamanolis,2004). ThemajorityofthebuildingstockinGreece,duetotheoldnessoftheconstruction,hassingleglazedwin-dows. Only recently national energy improvement pro-grammes–“SavingatHome”,2011-tookplaceinordertoimprovetheperformanceofthebuildingenvelope(Gele-genisetal,2013).Oneofmostpopularmeasuresappliedwastoreplacesingleglazedwindowswithdoubleglazedones. In newly constructed apartment buildings the appli-



Figure 06: Multi-storeyapartment building inThessaloniki from1980s(Source: Author)

Figure 07: Multi-storey apartment building in Thessaloniki from 2000s (Source: Author)

cationofdoubleglazedwindowsisinawaymandatoryinordertoachievetheregulationstandards.

materials (insulatingmaterials) can almost eliminate theheattransfer(Jones,2008).Dependingonclimaticcondi-tions,excessiveinsulationmayleadtooverheatingduringhot summer periods. Thermal mass is called the part of the building which is able to store heat during the daytime and release it back in the space when the sun is no longer present (Baker,2007).Thermalmasscanalsobeconsideredasthe building’s thermal battery.The ability of thematerialto store heat from its environment as defined by Jones(2008)canbecalculatedfromtheformula:

As it ispreviouslypresented, the twomainhigh-lightsoftheGreekdomesticbuildingstockisononehandthe lack of insulation and on the other the existence of high thermal mass. Consequently, the condition and the physical characteristics of the building fabric undertake a fundamental role affecting the energy performance of theconstruction.Thebuildingenvelope takes theroleofa“filter”,beingthepartthatdealswithandmanagestheinterchanges between the internal and external conditions (Jones,2008). ThermalinsulationasdefinedbySzokolayisoneof the most important techniques for controlling the heat transfer. Its main role is to de-couple the interior spaces fromtheexterioronesbyradicallymitigatingtheheatflowfrom warmer towards colder spaces through the building envelope.Inclimatesthatcoldwinterperiodsarefollowedbyhotsummers,theroleofinsulationisbeneficialforallyearlong(Zold,Szokolay,1997). Insulation can be found as external, internal or cavityoneanditisusuallyappliedtoallthesurfacesthatareexposedtotheexteriorenvironment.Insulatingmate-rialsarecharacterizedby theheat transfermechanisms.Conductivityisveryimportantbecausenormallyappliestoheat transfer through solids. The rate of the heat transfer depends on its thermal conductivity or k-value,which isgenerally related to the density of the material. High-den-sitymaterialswithhighk-values,likeconcreteandmetals,allows heat to pass through them, whereas low-density

4. THERMAL MASS AND INSULATION

Thermal capacity (J/K·m3) = Volume (m3) x Density (kg/m3) x Specific Heat (J/kg·K)

Diurnal temperatures cycles usually affects only thefirstthicknessofthematerial,becausethedeeperintothematerial,thelessheatflowsintoitinashortperiodoftime(Baker,2007).Thisgivesindicationsontheeffective-ness of thermal mass distribution inside a space (Figure 08).Inorderforthethermalmasstobeusefulandefficient,the surface that is coupledwith the interior environmentshouldbelarge.Interior,finishingslikesuspendedceilingsandflooringswithcarpets,compromisesitsefficiency. Another important characteristic of thermal mass is the response of the building to the outdoor conditions andthevariationsoftemperature(Figure09).Thediffer-encesbetweenheavyweightandlightweightstructuresarefound in the fluctuation/stabilization and the respectivelypeaks of indoor temperature within a diurnal cycle and in thewarm-upandcool-downrate(Yannas,1994). During the winter period a better use of the solar and internal gains can be made, as the space heats up gradually throughout the day and is able to release back



the absorbed heat later during the night when is actually needed. Hence, the period when the mechanical heating system is desired can be decreased. During summer the processisquitesimilar.Duringdaytimeexcessiveheatisstored into the structure of the building, keeping as low as possible the indoor temperatures. Later in the night, thisheatmustbetakenoutbyusingpassivecoolingtech-niques(Baker,2007). The solar control and the protection from heat gains using shading devices, the cooling process of thesurfaces by the means of natural ventilation and themoderation of heat flows and daily swings in the indoortemperature by the thermal mass can be considered as passive cooling techniques (Santamouris, 2003). In par-ticular,night-ventilationcanbereallyefficientforbuildingswithhighthermalcapacity(Santamouris,2007).Asstated,night-ventilationcanmitigatenotonlythepeakindoortem-peratures, but also the temperature within a diurnal cycle, helping the building, especially during morning hours, to havealowertemperaturekickstart.Atimelagbetweenthepeak indoor and outdoor temperature is also observed.Night-ventilationcanbeeffectiveincaseswherethereisanadequate temperaturedifferenceandsufficientexpo-sure of thermal mass.

Figure 08: Alternativethermalmassdistribution(Source: Baker, 2007)

(a)concentratedthermalmass

(b)mosteffectivethermalmass

(c)leasteffectivethermalmass

Figure 09: Heavyweight and lightweight building response (Source: Baker, 2007)

5.1. Recommendations of the EPCs

5. PRECEDENT STUDIES

AsitisalreadystatedandalsopresentedbyGe-legenisetal.(2013),theEnergyPerformanceCertificationprocessmayhaveuptotwophases.Duringthefirstphasetheoverallperformanceofthebuildingisbeingassessedbased on its usage and the calculation of the primary en-ergy consumption and the respectively CO2 emissions.Incase thebuilding iscategorized ina lowerclass thanclassB,thenatasecondphaseimprovementmeasuresare proposed by independent energy inspectors. The pro-posed measures could concentrate on (a) the improve-mentofthebuildingenvelope,inanattemptofmitigatingthe heat-exchanges between the interior and the exterior environment,(b)upgradingtheexistingheatingandcool-ing mechanical equipment as nowadays more efficientsystemsareout in themarket, (c) theuseof renewableenergy sources in order to decrease the fuel consumption andelectricityand(d)buildingmanagementsystems. In line with the study, only the 33% of the issued EPCs are dealing with the improvement of the buildingfabric, a measure that is broadly known for its cost-effec-tivenessand its retrofittingefficiency.Figure10presentsthe usual improvement recommendations and their fre-quency of appearance. The most dominant measure, ac-counting for the 67.2% by itself, focuses on the installation or replacementofSWHsystems.Aspartof thebroadercategory of the exploitation of renewable energy sources, such measures seem to be the easy solution as they can easily upgrade the energy class of the building, since it is based on the substitution of electricity with solar energy and thereforeprimaryenergyconsumption issignificant-



ly reduced (Gelegenisetal,2013).The insulationof theexteriorwalls,which isavital, lessexpensiveandmoreefficientmeasure,accountsonlyforthe20.6%,whilethethermal insulation of the roofs for the 10.3%.

Figure 10: Detailed analysis of the frequency of appearance of the most often recommended measures in obligatory EPCs (Source: Gelegenis et al, 2013)

It can be assumed that the EPCs direction is strongly affected by the construction industry and its ad-ministrative processes affects its fundamental goals. In-stead of promoting high-cost measures, attention should begiventothe improvementof theexisting,poor-qualitybuilding fabric through simpler and noteworthy interven-tions.

5.2. Measures for efficient energy saving and CO2 re-duction

Theimprovementoftheenvelopeofthebuildings,whichactsasthe“modifier”,shouldbeafirst-come-to-mindmeasure in order to control the heat-exchanges, increase theenergysavingsthoughout theyearandminimizetheCO2 emissions (Jones, 2008). Taking into account thepoor condition of the fabric of themajority of theGreekdwellingstheapplicationofinsulationisthefirstinterven-tionthatshouldbeimplemented.Inreferencewithevalu-ationsofvariousenergysavingmethods,theinsulationofthe walls, especially of the external facades of the building, isthemosteffectiveonewithenergysavingsreaching33-60% of the energy consumption for heating (Balaras et al, 2005). In general, the external thermal insulation is the most preferable one due to the forthright deal with con-structionaldetailssuchasthermalbridges,thepreserva-tion of the useful thermal mass of the bearing structure and theavoidanceofpossiblecondensationwithin thewalls.

However,sometimestheexternalinsulationconfigurationcannot be applied and therefore an internal one must be considered. The side on which the insulation panels would beplacedcancompletelychangethefinalperformanceofthe space. Recent analysis has been carried out concern-ing the comparative assessment betweenexternal (ETI)and internal (ITI) insulation configuration (Figure 11) fordomestic building refurbishments in climatic regions both innorthernGreeceaswellasinthesouthernpartofthecountry (Kolaitis et al, 2012). The study also takes intoconsideration a different behavioral occupancy pattern,an ‘active’ occupant behavior (ACT) that the occupantsintervene in theirenvironmentandapassiveone(PAS).Generally, it is found that the performanceof theETI isbetterthantheITI.Inspecific,duringthewinterperiodtheheatingloadsarereducedsignificantlyinbothcasescom-paredtoanuninsulatedbuilding,withtheETIconfigurationhavingslightlybetteroverall resultsas itallowsalso theuse of the thermal mass of the structure. The interesting outcomes are found during the summer period, when the cooling loads after the installation of either ETI or ITI are increasing(Table01).Hereisthepointwherethebehavioroftheoccupantsbecomesessential,asitisobviousthatthe‘active’occupantsareabletoreducesignificantlytheenergyconsumptionandpreventoverheatingrisksduringthe hot summer periods.

Figure 11: Wallassemblies:noinsulation(left),externalthermalinsula-tion(middle)andinternalthermalinsulation(right)(Source: Kolaitis et al, 2012)

ItisproventhattheGreekbehavioralpatternsareinfavorofthe‘active’occupantattitude.Occupantsintheirresidencesareusedtointeractwiththeirenvironmentandmorespecificwithwindowsandshadingdevices(Drakou,Tsangrassoulis, 2012). Among the surveyed occupants,the60%openthewindowsinsummersinordertoimprovetheairquality,whilethe35%arealsoawareofthepreven-tionoftheoverheating.Thepercentagesoftheoccupantsthat interact in a daily basis with the windows and consider theoptionofcross-ventilationandnight-ventilationpossi-blearealsoveryhigh. AsmentionedbySantamourisetal,(2010),nightventilationisingeneraloneofthemosteffectivepassivecooling techniquesandmaydecreaseupto40KWh/m2theannualcoolingloadinresidentialbuildings.Itisproventhat up to a 3°K reduction of the peak indoor temperature canbeobserved, if thepreviousnightanight-ventilation



Table 01: Normalizedannualenergydemandforalltheexaminedtestcases(Source: Kolaitis et al, 2012)

technique had occurred. Nevertheless, night-ventilationisstronglybasedontheexploitationoftheavailableuse-ful thermal mass of a building, the temperature difference betweentheinteriorspaceandtheexteriorenvironment,and the temperature difference of the external air within a diurnal cycle. Consequently, the potential of this technique might be compromised by the heat island effect which is apparentinthedenseurbanareasoftheGreekcities. Even in situationswhen natural ventilation tech-niquesarenotveryefficientthethermalmassofthebuild-ing can counterbalance to some extent the overheatingrisks.Heavyweightstructureshavetheabilitytostoretheheat inside their fabric, keeping in this way the indoor tem-peratureslower.Sakkaetal(2012)analyzedtheperform-ance of free-running low-income houses in Athens during theextremeheatwaveofthesummerof2007.Itwasfoundthatbuildingsofhighthermalmasshaveakindof“climaticmemory”. Their performance depends on a broader period oftimeandtheyarenotsignificantlyaffectedbyshort-termclimatechanges,suchasthefirstdaysofheatwaves.

pacity bearing structure and well applied thermal insulation can lead to a substantial reduction of the dependence on auxiliary heating and cooling systems. However, recentstudiespresent that thecurrentenergyefficiencyproceduresthatoccurinGreecedonothave the desired results. Proposed improvementmeas-ures do not focuses on the condition of the building fabric, but tend tobemarketdriven,promoting theprofitof thehigh technology industry.ThisputsGreece in thewrongwayand theriskof failing to fulfill the2020goals isevi-dent.Simplerandmoreefficientmeasuresthatdealwiththecoreoftheproblemandfocusontheimprovementofthebuildingenvelopemustbeconsidered. A more straightforward adoption of the proposed guidelines and legislation must occur in order to start dis-cussing about a smart and sustainable growth in the coun-try.

During the last years a worldwide interest in re-ducing the carbon footprint of cities is being shown. Among the global community, the European Union has set a forth-comingtargetaccompaniedbyaDirectivetowardsalltheMemberStates,withtheintentiontodecreasethelevelsoftheCO2emissionsandthegreenhousegases.InGreece,thecurrentenergyefficiencylegislationfocusesonthecat-egorizationbothoftheexistingbuildingstock,aswellasof any possible new constructions to energy classes. In case the buildings do not meet the minimum standards, improvementmeasurementsarebeingproposed. TheexistingdomesticbuildingstockofGreeceischaracterizedbyitsoldageandpoorqualityofthebuildingenvelope.Themajorityoftheapartmentblocksarestruc-tures of high thermal capacity and no insulation. Only re-centlyconstructedbuildingshavesufficientlevelsofther-mal insulation. It is widely accepted that the role of the building fabric isverysignificant for theultimateenergyperform-anceofthebuilding.Thebuildingenvelopeistheinterme-diate between the interior and the exterior environment,and consequently it is responsible for the thermal comfort of the occupants. The combination of a high thermal ca-

6. CONCLUSIONS

IwouldliketothankalltheAASEDteachingstaffandvisitinglecturers(SimosYannas,PaulaCadima,Gus-tavo Brunelli, Jorge Rodriquez, Nick Baker and JoanaGonçalves),whowere very supportive and encouragingthroughout the term. I would also like to offer my special thanks to my tutor, Mariam Kapsali for her help and guid-ance through the RP1 tutorials.

ACKNOWLEDGEMENTS



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Thermal Mass & Insulation: Domestic Buildings in the Mediterranean Climate

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