aber1EDITOR-IN-CHIEF MAT SANTAMOURISAdvances in Building Energy Research Advancesi nBui l di ngEnergyResearchABER_prelims4/22/0712:05 PMPage iEditor-in-Chief Mat SantamourisUniversity of Athens, GreeceEditorial BoardProfessor O. SeppanenTechnical University of Helsinki, FinlandDr M. ShermanLawrence Berkeley Laboratory, USAN. FintikakisAssociate Editor for UIA, GreeceDr P. WoutersBelgian Building Research Institute, BelgiumProfessor F. AllardUniversity of La Rochelle, FranceDr H. AkbariLawrence Berkeley Laboratory, USAProfessor E. MaldonadoUniversity of Porto, PortugalProfessor Lee S. E.University of Singapore, SingaporeProfessor A. PapadopoulosAristotle University of Thessaloniki, GreeceProfessor F. NicolsUniversity of Strathclyde, UKDr E. ErellBen Gurion University, IsraelProfessor H. YoshinoTohuku University, JapanProfessor F. HaghighatConcordia University, CanadaProfessor R. LambertsUniversity of Santa Catharina, BrazilProfessor J. ClarkeUniversity of Strathclyde, UKProfessor A. AthienitisConcordia University, CanadaProfessor J. KhedariUniversity of Bangkok, ThailandProfessor F. ButeraTechnical University of Milan, ItalyProfessor M. WilsonMetropolitan University, LondonProfessor K. VossUniversity of Wuppertal, GermanyABER_prelims4/24/0711:20 AMPage iiAdvancesi nBui l di ngEnergyResearchVolume 1Editor-in-Chief Mat SantamourisLondon Sterling, VAABER_prelims4/22/0712:05 PMPage iiiFirst published by Earthscan in the UK and USA in 2007 Copyright Mat Santamouris, 2007All rights reservedISSN 1751-2549ISBN 978-1-84407-389-4Typeset by Domex e-Data, IndiaPrinted and bound in the UK by Cromwell Press, TrowbridgeCover design by Giles SmithFor a full list of publications please contact:Earthscan812 Camden High StreetLondon, NW1 0JH, UKTel: +44 (0)20 7387 8558Fax: +44 (0)20 7387 8998Email: earthinfo@earthscan.co.ukWeb: www.earthscan.co.uk22883 Quicksilver Drive, Sterling, VA 20166-2012, USAEarthscanisanimprintofJamesandJames(SciencePublishers)Ltdandpublishesinassociation with the International Institute for Environment and DevelopmentA catalogue record for this book is available from the British LibraryLibrary of Congress Cataloging-in-Publication DataAdvances in building energy research / editor-in-chief, Mat Santamouris.v. cm.Includes bibliographical references.ISBN-13: 978-1-84407-389-4 (hardback)ISBN-10: 1-84407-389-0 (hardback)1. BuildingsEnergy conservation. I. Santamouris, M. (Matheos), 1956-TJ163.5.B84A285 2007696dc222007004087ThepaperusedforthisbookisFSC-certified.FSC(the Forest Stewardship Council) is an internationalnetwork to promote responsible management of theworlds forests.ABER_prelims4/22/0712:05 PMPage ivContentsList of figures viiList of tables ixList of acronyms and abbreviations xi1 On the Typology, Costs, Energy Performance,Environmental Quality and Operational Characteristicsof Double Skin Faades in European Buildings 1Wolfgang Streicher, Richard Heimrath, Herwig Hengsberger,Thomas Mach, Reinhard Waldner, Gilles Flamant, Xavier Loncour,Grard Guarracino, Hans Erhorn, Heike Erhorn-Kluttig, MatheosSantamouris, Ifigenia Farou, S. Zerefos, M. Assimakopoulos,Rogrio Duarte, ke Blomsterberg, Lars Sjberg andChrister Blomquist2 Artificial Intelligence in Buildings: A Review of theApplication of Fuzzy Logic 29D. Kolokotsa3 Field Studies of Indoor Thermal Comfort and theProgress of the Adaptive Approach 55Michael A. Humphreys, J. Fergus Nicol and Iftikhar A. Raja4 Typical Weather Years and the Effect of UrbanMicroclimate on the Energy Behaviour of Buildingsand HVAC Systems 89S. Oxizidis, A. V. Dudek and N. Aquilina5 Energy Cost and its Impact on Regulating BuildingEnergy Behaviour 105Agis M. Papadopoulos6 Heat Island Research in Europe: The State of the Art 123Mat Santamouris7 Post-occupancy Evaluation and Thermal Comfort: Stateof the Art and New Approaches 151Elke Gossauer and Andreas Wagner8 High Dynamic Range Imaging and its Application inBuilding Research 177Axel Jacobs9 Use of Satellite Remote Sensing in Support of UrbanHeat Island Studies 203M. Stathopoulou and C. CartalisABER_prelims4/22/0712:05 PMPage v10 Thermal Behaviour of the Diffusive Building Envelope:State-of-the-Art Review 213Kai Qiu, Fariborz Haghighat and Gerard Guarracino11 A Review of ESP-rs Flexible Solution Approach andits Application to Prospective Technical DomainDevelopments 227J. A. Clarke, N. J. Kelly and D. Tangvi ADVANCES IN BUILDING ENERGY RESEARCHABER_prelims4/22/0712:05 PMPage viList of Figures and TablesFIGURES1.1 Steiff factory, Giengen/Brenz, Germany 41.2 Buildings analysed within the BESTFAADE project 71.3 The typical Belgium DSF within the multitude of varieties 91.4 Utilization of BESTFAADE buildings121.5 Implementation and orientation of faades within BESTFAADE 121.6 Type of ventilation and partitioning of the gap 131.7 Types of room heating device and energy source used in BESTFAADE buildings 161.8 Types of room cooling device and energy source used in BESTFAADE buildings 161.9 Ventilation and air conditioning of BESTFAADE buildings 171.10 Ventilation openings in outer shell of analysed faades 171.11 Ventilation openings in inner shell of analysed faades 181.12 Airflow in the gap in summer (above) and in winter (below) 181.13 Integration of different devices into the faades 221.14 Cost of DSFs compared to conventional faades 231.15 Additional cost of DSFs according to different authors 232.1 The structure of the fuzzy logic controller 302.2 The structure of an office building HVAC 373.1 Scatter plot of PMV and SET for the de Dear data 623.2 Scatter plot of PMV and SET for the SCATs data 623.3 Scatter plot of standardized mean response and meanroom temperature 633.4 Scatter plot of mean warmth vote against mean operativetemperature for the buildings in the de Dear database 643.5 Scatter plot of mean warmth vote against mean operativetemperature for the files 653.6 Scatter plot of mean warmth vote against mean operative temperature for the SCATs database. 663.7 Scatter plot of mean vote against mean operative temperaturefor data from monthly surveys in various cities in Pakistan663.8 Scatter plot of mean vote against mean operative temperaturefor all surveys listed in Table 3.1 673.9 Mean clothing insulation and mean room temperature683.10 Probability of use of various building controls: Variation with outdoor temperature693.11 Illustration of the regression procedure: Scatter plot of subjective warmth and operative temperature703.12 Scatter plot of regression coefficients of warmth vote onoperative temperature, against the standard deviation of theoperative temperature (de Dear database) 71ABER_prelims4/22/0712:05 PMPage viiviii ADVANCES IN BUILDING ENERGY RESEARCH3.13 Scatter plot of regression coefficients of warmth vote on operative temperature, against the standard deviation of the operative temperature (SCATs database) 723.14 Summary of mean values of the regression coefficients (/K), in relation to the standard deviation of the operative temperature, from the de Dear and the SCATs databases 743.15 Proportion of people likely to be comfortable 763.16 Scatter plot of neutral temperatures against the mean operative temperature773.17 Chart showing the effects of indoor and outdoor temperature on the preferred point on the ASHRAE scale 793.18 Scatter plot for neutral temperatures for the 1978 data 803.19 The dependence of the neutral temperature on the prevailing outdoor mean temperature for the free-running and the heated/cooled modes ofoperation814.1 Design and typical weather 914.2 The ATREUS methodology diagram 1005.1 Development of oil prices since 1970 1065.2 Evolution of heating energy consumption in German buildings, according to the five steps approach of Gertis 1075.3 Development of average insulation thickness for walls, as foreseen by national regulations, in European countries1085.4 Wall insulation thickness in European national regulations, 2003 1105.5 Development of minimum ventilation rates in the US 1115.6 Development of electricity consumption and its annual growth rate in European countries1135.7 Possible combinations of solar thermal and sorption refrigeration technologies 1177.1 Cause-and-effect approach for field studies of thermal comfort during the 1970s 1547.2 Cause-and-effect approach for field studies of thermal comfort in the 1980s 1547.3 Cause-and-effect approach for field studies of thermal comfort in the 1990s 1557.4 General procedure of building surveys 1627.5 Correlation between mean satisfaction with temperature and weightedimportance of temperature for general satisfaction with the workplace (Spearman correlation) 1708.1 The image acquisition pipeline 1788.2 Igreja Nossa Senhora de Fatima, Lisbon 1798.3 Sequence of exposure-bracketed images, separated by one f-stop 1808.4 Inability of a single LDR photograph to capture the huge dynamic range of luminance in our environment180ABER_prelims4/22/0712:05 PMPage viiiLIST OF FIGURES AND TABLES ix8.5 Polynomial response curves for selected digital cameras 1838.6 The information that can be gained from HDR images and its accuracy depend on the level of calibration 1858.7 Reduction of image brightness of a fisheye lens image away from the optical axis1868.8 Linearly tone-mapped image with gamma correction of the church scenedisplayed with pfsview1898.9 Results of different tone-mapping operators 1908.10 DR 37P HDR display by BrightSide 1918.11 The output of the BrightSide display is a combination of the LED array (low spatial frequency) and the LCD modulation (high spatial frequency) 1928.12 Interactive luminance map in a web browser 1928.13UGR meter developed by Technical University of Ilmenau 1948.14 Screenshot of the software of the UGR meter 1958.15 Panoramic HDR capturing system1958.16 HDR panorama of Air Zermatt 1968.17 The conversion of light to a digital value in a digital camera 1968.18 Extended dynamic range of the Fujifilm SuperCCD sensor 1978.19 CCD sensor technology 1978.20 CMOS imaging sensor 19810.1 Dynamic U-value with velocity21910.2 Comparison of experiment data and analytical model results 22211.1 The future time row matrix, A, for the simple room model as shown23011.2 Partitioning of the A coefficients matrix 23111.3 Block partitioning of A 23211.4 Iterative solution of nested domains 238TABLES1.1 DSF buildings analysed within the BESTFAADE project82.1 Summary of fuzzy logic in thermal sensation modelling 322.2 Summary of fuzzy logic control in thermal comfort applications342.3 Summary of fuzzy logic in energy consumption and HVAC systems412.4 Performance of the zone-level fuzzy controllers for one-day simulation452.5 Evaluation of the energy conservation for the buildings in Crete and Athens, Greece462.6 Summary of fuzzy logic in hybrid applications473.1 Thermal comfort databases used in this review 583.2 Scales of warmth and preference 593.3 Pearson correlation coefficients for the warmth scale and the principal indices 613.4 Residual standard deviations after regression 754.1 Weighting factors for the selection of representative months during the creation of typical weather years 94ABER_prelims4/22/0712:05 PMPage ix6.1 Results of heat island studies of European cities1251287.1 Post-occupancy studies mainly related to research in thermal comfort and its predictive parameters 1597.2 Post-occupancy studies mainly related to research in the field of sick building syndrome 1597.3 Post-occupancy studies for benchmarking and performance feedback 1607.4 Field experiment methodology of ASHRAE RP-1161 1637.5 Field experiment methodology of the SCATs project 1647.6 Field experiment methodology of the PROBE project 1657.7 Field experiment methodology of the ProKlima project 1667.8 Field experiment methodology of the HOPE project 1677.9 Field experiment methodology of the CBE 1688.1 Comparison of image size and quality for various file formats1888.2 Comparison of CCD and CMOS imaging chips 198x ADVANCES IN BUILDING ENERGY RESEARCHABER_prelims4/22/0712:05 PMPage xList of Acronyms andAbbreviationsAC air-conditionedADHRIA Automated High Dynamic Range Imaging AcquisitionAEB auto-exposure bracketingAHU air handling unitAI artificial intelligenceANFIS adaptive neural fuzzy inference systemANN artificial neural networksBBRI Belgian Building Research InstituteBEMS building energy management systemBLHI boundary layer heat islandBMS building management systemBREEAM BREs Environmental Assessment MethodBSI British Standards InstitutionBUS Building Use StudiesCBE Center for the Built EnvironmentCCC Confederation of Construction ClientsCCD charge coupled deviceCDD cooling degree dayCF concentrated flowCFC chlorofluorocarbonCFD computational fluid dynamics CGF conventional glass faadeCHP combined heat and powerCIBSE Chartered Institute of Building Services EngineersCLC CORINE Land CoverCLHI canopy layer heat islandCMOS complementary metal oxide semiconductorCOP coefficient of performanceCRI compositional rule of inferenceCWEC Canadian Weather for Energy CalculationsDAI distributed artifical intelligenceDF diffuse flowDGI daylight glare indexDGP daylight glare probabilityDI discomfort indexDID degree of individual dissatisfactionDP differential pressureDSF double skin faadeEEM energy efficiency measureEPBD Energy Performance of Buildings Directive ABER_prelims4/22/0712:05 PMPage xiET effective temperatureEV exposure valueEXIF exchangeable image file format FCU fan coil unitFFSI functioning fuzzy-subset inferenceFLC fuzzy logic controllerF-PID fuzzy proportional integral derivativeFSC fuzzy satisfactory clusterFTC fault-tolerant supervisory controlGA genetic algorithmsGIS geographic information systemGP genetic programmingGWP global warming potentialHC hydrocarbonHCFC hydrochlorofluorocarbonHDD heating degree dayHDH heating degree hourHDRI high dynamic range imagingHFC hydrofluorocarbonHOPE Health Optimisation Protocol for Energy-efficient BuildingsHVAC heating, ventilation and air conditioningHY historical yearIAQ indoor air qualityIEQ indoor environmental qualityIHEE infiltration heat exchange efficiencyIWEC International Weather for Energy CalculationsLCD liquid crystal displayLDR low dynamic rangeLED light-emitting diodeLEE least enthalpy estimatorLEED Leadership in Energy and Environmental DesignLST land surface temperatureMEC manual exposure correctionMMPC multiple model predictive controlMUHI micro-urban heat islandNDVI normalized difference vegetation indexNN neural networkNV naturally ventilatedODP ozone depletion potential PD proportional derivativePDA personal digital assitantPI proportional integralPID proportional integral derivativePMV predicted mean votexii ADVANCES IN BUILDING ENERGY RESEARCHABER_prelims4/22/0712:05 PMPage xiiPPD percentage of people dissatisfiedPROBE Post-occupancy Review of Buildings and their EngineeringPSD proportional sum derivativePSF point spread functionPV photovoltaicRAC room air-conditionerRBF radial basis functionRES renewable energy sourcesREV representative elementary volumeRMSE root mean square errorSBS sick building syndromeSCATs Smart Controls and Thermal Comforts.d. standard deviationSDK software development kits.d.m. standard deviation meanSET standard effective temperatureSUHI surface urban heat islandSVD singular value decompositionSWOT strengths, weaknesses, opportunities and threatsSY synthetic yearTCL thermal comfort levelTMM typical meteorological monthTMY typical meteorological yearTRDTS testing room dynamic thermal systemTRY test reference yearTSV thermal sensation voteTWY typical weather yearTY typical yearUGR unified glare ratingUHI urban heat islandUSB universal serial busVDSF ventilated double skin faadeVOC volatile organic compoundWYECWeather Year for Energy CalculationsLIST OF ACRONYMS AND ABBREVIATIONS xiiiABER_prelims4/22/0712:05 PMPage xiiiABER_prelims4/22/0712:05 PMPage xivADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128Abstract The project BESTFAADE, sponsored by the Energy Intelligent Europe programme of theEuropean Union, and led by MCE-Anlagenbau, Austria, accumulated the state of the artof double skin faades (DSFs) in seven European countries (Austria, Belgium, France,Germany, Greece, Portugal and Sweden). Twenty-eight faades of different buildings inall partner countriesof BESTFAADEhavebeenanalysedfor theaspects, typesoffaadeindifferent countries, DSFsindifferent climaticregionsof Europe, existingsimulationsandmeasurements, thermal behaviour, indoor air quality, comfort, useracceptance, energydemandandconsumptions, control strategies, integratedbuildingtechnology, cost (investment, maintenance and operation), resource conservation,environmental impact, comparison to conventional glass faades (CGFs), integration ofrenewableenergysourcesintoDSFs, aswell asnon-energyrelatedissues, suchas,acoustics, aesthetics, fire protection, moisture, corrosion, durability, maintenance andrepair. Most of thebuildingsareofficebuildings, followedbyschoolsandservicebuildings. Nearlyall of thebuildingshavemechanical ventilationsystems, andbothheatingandcoolingareperformedmostlybyairheating/coolingsystems. Thetypesof faades are mainly multi-storey and corridor types; in Belgium juxtaposed modulesare frequently used. The faade gaps are mostly naturally ventilated (except forBelgium, wheretheindoor air is ledby mechanical ventilationviathegaptothe1On the Typology, Costs, EnergyPerformance, EnvironmentalQuality and OperationalCharacteristics of Double SkinFaades in European Buildings Wolfgang Streicher, Richard Heimrath, Herwig Hengsberger,Thomas Mach, Reinhard Waldner, Gilles Flamant, XavierLoncour, Grard Guarracino, Hans Erhorn, Heike Erhorn-Kluttig, Matheos Santamouris, Ifigenia Farou, S. Zerefos, M. Assimakopoulos, Rogrio Duarte, keBlomsterberg, Lars Sjberg and Christer BlomquistABER_Ch_014/3/074:34 PMPage 1 Keywords double skin faade; typology; technology; costs; performanceINTRODUCTIONInnovativefaadeconceptsaretodaymorerelevantthanever.Thedemandfornaturalventilationincommercialbuildingsisincreasingduetogrowingenvironmentalconsciousnesswhile,atthesametime,energyconsumptionforbuildingshastobereduced.Anadvancedfaadeshouldallowforacomfortableindoorclimate,soundprotectionandgoodlighting,whileminimizingthedemandforauxiliaryenergyinput.Double skin faades (DSFs) have become an important and increasingly used architecturalelement in office buildings over the last 15 years. They can provide a thermal buffer zone,solarpreheatingofventilationair,energysaving,sound,windandpollutantprotectionwithopenwindows,nightcooling,protectionofshadingdevices,spaceforenergygaining devices, such as, photovoltaic (PV) cells, and differentiated aesthetical qualities,which is often the main argument in their favour. CommercialandofficebuildingswithintegratedDSFscanbeenergyefficientbuildingsprovidingallthequalitieslistedabove.However,notallDSFsbuiltinrecentyearsperformwell.Farfromit,inmostcaseslargeair-conditioningsystemshavetocompensateforsummeroverheatingproblemsandenergyconsumptionoftenexceedstheintendedheatingenergysavings.Thereforethisarchitecturaltrendhas,inmanycases, resulted in a step backwards regarding energy efficiency and the possible use ofpassive solar energy. The project BESTFAADE, sponsored by the Energy Intelligent Europe programme ofthe EuropeanUnion,andledbyMCE-Anlagenbau,Austria,accumulatedthestateofthe artofdoubleskinfaadesinsevenEuropeancountries(Austria,Belgium,France,Germany, Greece, Portugal and Sweden). Twenty-eight faades of different buildings in allpartner countriesofBESTFAADEhavebeenstudiedbymeansofastandardizedquestionnaire.Thequestionnairecomprisesdataonlocation,informationaboutthebuilding and the faade, construction and airflow in the faade, as well as maintenanceand cost. The analysis has been drawn for the aspects, types of faade in different countries,DSFsindifferentclimaticregionsofEurope,existingsimulationsandmeasurements,thermalbehaviour,indoorairquality,comfort,useracceptance,energydemandandconsumptions,controlstrategies,integratedbuildingtechnology,cost(investment,maintenance and operation), resource conservation, environmental impact, comparison toCGFs,integrationofrenewableenergysourcesintoDSF,aswellasnon-energyrelatedissues,suchas,acoustics,aesthetics,fireprotection,moisture,corrosion,durability,maintenance and repair.2 W. STREICHER et alADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128centralizedair handlingunit). TheshadingisperformedmainlywithVenetianblindslocated in thegap. Unfortunately data on energy demand and temperatures areinfrequently measured and rarely available. The cost of DSFs is significantly higher thanconventional faades.ABER_Ch_014/3/074:34 PMPage 2DEFINITIONThe DSF concept has been specified in a number of definitions: Adoubleskinfaadecanbedefinedasatraditionalsinglefaadedoubledinsideoroutside by a second, essentially glazed faade. Each of these two faades is commonlycalledaskin.Aventilatedcavityhavingawidthwhichcanrangefromseveralcentimetrestoseveralmetresislocatedbetweenthesetwoskins.Automatedequipment,suchasshadingdevices,motorizedopeningsorfans,aremostoftenintegrated into the faade. The main difference between a ventilated double faade andanairtightmultipleglazing,whetherornotintegratingashadingdeviceinthecavityseparatingtheglazing,liesintheintentionalandpossiblycontrolledventilationofthecavity of the double faade. (BBRI, 2004)[DSFs are] essentially a pair of glass skins separated by an air corridor. The main layerof glass is usually insulating. The air space between the layers of glass acts as insulationagainsttemperatureextremes,winds,andsound.Sun-shadingdevicesareoftenlocated between the two skins. All elements can be arranged differently into numbersof permutations and combinations of both solid and diaphanous membranes. (Harrisonand Meyer-Boake, 2003)TheDoubleSkinFaadeisasystemconsistingoftwoglassskinsplacedinsuchaway that air flows in the intermediate cavity. The ventilation of the cavity can be natural,fansupportedormechanical.Apartfromthetypeoftheventilationinsidethecavity,the origin and destination of the air can differ depending mostly on climatic conditions,theuse,thelocation,theoccupationalhoursofthebuildingandtheHVAC[heating,ventilation and air conditioning] strategy. The glass skins can be single or double glazingunitswithadistancefrom20cmupto2 meters.Often,forprotectionandheatextractionreasonsduringthecoolingperiod,solarshadingdevicesareplacedinsidethe cavity. Poirazis (2004)HISTORYThehistoryofDSFshasbeendescribedinseveralbooks,reportsandarticles.Saelens(2002) mentions that in 1849, Jean-Baptiste Jobard, at that time director of the IndustrialMuseum in Brussels, described an early version of a mechanically ventilated multiple skinfaade.Hementionshowinwinterhotairshouldbecirculatedbetweentwoglazings,whileinsummeritshouldbecoldair.Crespo(1999)andNeubert(1999)claimthat,thefirst instance of a double skin curtain wall appears in 1903 in the Steiff factory in Giengen/Brenz near Ulm, Germany (Figure 1.1). According to them, the priorities were to maximizedaylightingwhiletakingintoaccountthecoldweatherandthestrongwindsoftheregion. The solution was a three-storey structure with a ground floor for storage space andtwo upper floors used for work areas. The structure of the building proved to be successfulandtwoadditionswerebuiltin1904and1908withthesamedoubleskinsystem,but using5timber instead of steel in the structure for budget reasons. All buildings are stillin use.Double Skin Faades in European Buildings 3ADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128ABER_Ch_014/3/074:34 PMPage 3In 1903 Otto Wagner won the competition for the Post Office Savings Bank in Vienna,Austria. The building, built in two phases from 1904 to 1912, has a double skin skylight in themain hall. At the end of the 1920s double skins were being developed with other priorities inmind.Twocasescanbeclearlyidentified.InRussia,MoiseiGinzburgexperimentedwithdouble skin strips in the communal housing blocks of his Narkomfin building (1928) and LeCorbusier designed the Centrosoyus in Moscow. A year later, Le Corbusier started the designfor the Cite de Refuge (1929) and the Immeuble Clarte (1930) in Paris and postulated two newfeatures. First, la respiration exacte (... an exactly regulated mechanical ventilation system),and second, le mur neutralisant (... neutralizing walls are made of glass or stone or both ofthem. They consist of two membranes which form a gap of a few centimetres. Through thisgap,whichenvelopsthewholebuilding,airisconducted(hotairinMoscowandcoldinDakar). By that the inner surface maintains a constant temperature of 18C. The building ishermetically sealed! In the future no dust will find its way into the rooms. No flies, no gnatswill enter. And no noise!) (Le Corbusier, 1964). Little or no progress was made in double skin glass construction until the late 1970sand early 1980s. During the 1980s this type of faade started gaining momentum. Mostwere designed taking into account environmental concerns, like the offices of Leslie andGodwin.Inothercasestheaestheticeffectofthemultiplelayersofglasswastheprincipal concern. In the 1990s two factors strongly influenced the proliferation of DSFs.Environmentalconcernsstartedinfluencingarchitecturaldesignbothfromatechnicalstandpointandasapoliticalinfluencethatmadegreenbuildingsagoodimageforcorporate architecture (Poirazis, 2004). TECHNICAL DESCRIPTIONFAADE CONSTRUCTION The choice of the glass type for the interior and exterior panes depends on the typologyofthefaade.Inthecaseofafaadeventilatedwithoutdoorair,aninsulatingpane(athermalbreak)isusuallyplacedattheinteriorandasingleglazingattheexteriorside.4 W. STREICHER et alADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128FIGURE 1.1 Steiff factory, Giengen/Brenz, GermanySource: Neubert (1999)ABER_Ch_014/3/074:34 PMPage 4However, in the case of a faade ventilated with indoor air, the insulating pane is usuallyplacedattheexteriorwhilethesingleglazingisattheinteriorside.Forsomespecifictypesoffaade,theinternalglasspanecanbeopenedbytheusertoallownaturalventilation of the building.Theventilationofthecavitymaybetotallynatural,fansupported(hybrid)ortotallymechanical. The width of the cavity can vary as a function of the applied concept between10cmtomorethan2m.Thewidthinfluencesthephysicalpropertiesofthefaadeandalso the way that the faade is maintained. If cleaning of all faade panes is not possiblefrom inside and outside of the building, the width of the cavity has to be about 80cm toallow cleaning personal to access the gap. In this case the airflow in the gap has less flowresistance and can therefore be higher compared to a narrow gap. However, more rentedor sold space of the building is lost.Shading devices can be placed inside the cavity for protection. Often venetian blinds canbe used. The characteristics and position of the blind influence the physical behaviour of thecavity because the blind absorbs and reflects energy from radiation. Thus, the selection ofthe shading device should be made after considering the proper combination between thepane type, the cavity geometry and the ventilation strategy and has a high impact on thedaylight situation within the rooms behind. Openings in the external and internal skin andsometimes ventilators allow the ventilation of the cavity. The choice of the proper pane typeandshadingdeviceiscrucialforthefunctionoftheDSFsystem.Differentpanescaninfluence the air temperature and thus the flow in the case of a naturally ventilated cavity. The geometry (mainly width and height of the cavity) and the properties of the blinds(absorbance, reflection and transmission) may also affect the type of airflow in the cavity.When designing a DSF it is important to determine the type, size and position of interiorand exterior openings of the cavity since these parameters influence the type of airflowand the air velocity and thus the temperatures in the cavity (more important in high-risebuildings). The design of the interior and exterior openings is also crucial for the indoorflow and consequently the ventilation rate and the thermal comfort of the occupants.ItisreallyimportanttounderstandtheperformanceoftheDSFsystembystudyingthe physics of the cavity. The geometry of the faade, the choice of the glass panes andshading devices and the size and position of the interior and exterior openings determinethe use of the DSF and the heating, ventilation and air-conditioning (HVAC) strategy thathas to be followed in order to succeed in improving the indoor environment and reducingenergyuse.Theindividualfaadedesignandproperfaadeintegrationarekeytohighbuilding performance.Comparedtotraditionalofficebuildings,especiallywithlargeglazedfaades,officebuildings with DSFs can have the following potential advantages: Individual window ventilation is almost independent of wind and weather conditions,mainly during sunny winter days and the intermediate season (spring and autumn). Heating demand is reduced thanks to preheating of outdoor air. Night cooling of the building by opening the inner windows is possible if the faadeis well ventilated. Security is improved thanks to the two glazed skins.Double Skin Faades in European Buildings 5ADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128ABER_Ch_014/3/074:34 PMPage 5 There is better sound proofing from external noise sources, for example, at locationswith heavy traffic, mainly during window ventilation. Exterior (intermediate) solar shading is more efficient, as the shading can also beused during windy days. There is potential for the protection of existing faades in renovation applications.Potential problems with office buildings with DSFs can be: poorer cross-ventilation and insufficient removal of heat from the offices roomsduring windless periods, when ventilation is mainly provided by natural ventilation; hot summer/spring/autumn days leading to high temperatures in office rooms as aresult of window ventilation; higher investment cost; reduced office floor area; risk of sound transmission via the faade cavity from one office to another with openwindows additional cost due to cleaning; overestimated energy saving potential; more difficult fire protection, depending on the type of faade; loss of daylight and increase electric loads by lighting; and loss of possible cooling by window ventilation during spring and autumn (lowoutdoor temperatures).DOUBLE SKIN FAADE BUILDINGS AND HVACThere are two different approaches. First, a building with its own separate heating, coolingandventilatingsystem,whereasecondskinisaddedtothefaade;thecavityofthedouble skin faade is only ventilated from the outside and is built to reduce noise, housesolar shading and light redirection devices. Second, a building where the heating, coolingandventilatingsystemofthebuildingisintegratedintotheDSF,forexample,byventilating the building using the cavity of the DSF.Thesecondalternativeisoftenthemostcost-effectiveoption.TheriskofthefirstalternativeishavingabuildingwithacompleteconventionalHVACsystemsurchargedwiththeaddedcostofanexpensivefaade.AccordingtodifferentinvestigationsandtechnicalreportstherearesometechnicalbenefitswithaDSF,benefitswhichhaveanimpact on the HVAC system: All types of DSF offer a protected place within the air gap to mount solar shadingand daylight enhancing devices, which then can be used whenever necessary andthereby reduce the cooling load. One of the advantages DSF systems may have is that they allow natural (or fansupported) ventilation during some periods of the year, which will reduce the use ofelectricity for ventilation. In winter the cavity forms a thermal buffer zone that reduces heat losses and enablespassive thermal gain from solar radiation, which will reduce the heating load.6 W. STREICHER et alADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128ABER_Ch_014/3/074:34 PMPage 6 DSFs may enable natural ventilation and night-time cooling of the buildings thermalmass, which will reduce the use of electricity for ventilation and the cooling load. DSFs reduce noise from motor traffic, enabling natural ventilation without noiseproblems.EVALUATION OF VARIOUS FAADES LOCATION OF DSF BUILDINGS AND TYPOLOGY IN DIFFERENT COUNTRIESTable1.1andFigure1.2showthelocationsthe28faadesofdifferentbuildingsinallpartner countries of BESTFAADE, which have been studied by means of a standardizedquestionnaire.Thequestionnairecomprisesdataonlocation,informationaboutthebuildingandthefaade,constructionandrouteofairflowinthefaade,aswellasmaintenance and cost.InAustria,theaimwastocoverasmanyaspossibledifferentsizes,typesandutilizationsofbuildingswithDSFs,forexample,newlybuiltDSFsaswellasretrofittedones, offices as well as schools and museums. But unfortunately the smallest, the largestand the most extraordinary DSFs could not be researched, although the managers of thesebuildings showed high interest in joining the project at the beginning. The example of thesmall DSF is just two storeys high and is the retrofitting is of three faades of the controlroom of the fire station in Graz. The main purposes were to improve noise protection andthermalefficiency,andbothaimsaresaidtohavebeenachievedbytheattachedsinglepane faade with venetian blinds inside the gap. The building that would have been one ofthe largest researched buildings in the project, the 24-storey Uniqa Tower in Vienna, is saidto be one of the most interesting towers among the aspiring high-rise buildings in the citybecause of its HVAC concept and the good performance of its DSF. There will probably bea chance to get data from this tower in the near future. The third interesting building thatDouble Skin Faades in European Buildings 7ADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128FIGURE 1.2 Buildings analysed within the BESTFAADE projectSource: Streicher (2005) ABER_Ch_014/3/074:34 PMPage 7shouldhavebeencoveredistheKunsthausBregenz,whichiswellknownforitsarchitecture. Since the walls of this museum have to be opaque for presentation reasons,the DSF is used to provide daylight for special light ceilings in each storey.8 W. STREICHER et alADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128TABLE 1.1 DSF buildings analysed within the BESTFAADE project NO. COUNTRY PARTNER FACADENAME CITY ORIENTATION UTILIZATION1 BiSoP Baden S / N school2 Felbermayr Salzburg S office - n.p.3 Austria IWT Fachhochschule Kufstein NW school / office - n.p.4 Justizzentrum Leoben SE office - p.5 Schubertstrasse Graz SE office - n.p.6 Aula Magna Louvain-La-Neuve SE other7 Belgium BBRI Sony Zaventem NE / SW office - n.p.8 UCB Center Brussels NE / SW office - n.p.9 Cit Lyon NE office - n.p.10 France LASH-DGCB EAL Vaulx en Velin NE school11 Thiers Lyon E office - n.p.12 Mnchner Tor Munich N / S / E / W office - n.p.13 Germany IBP Geschftsgeb.Munich N / S / E / W office - n.p.Sd 1+414 Zentralbibliothek Ulm N / S / E / W library15 A-A Holdings Athens E office - n.p.16 Greece NKUA Alumil M5 Kilkis-Stavrochori E office - n.p.17 AVAX Athens E office - n.p.18 CGD Lisbon S office - n.p.19 Atrium Saldanha Lisbon SW office - n.p. / services20 Portugal ISQ ES Viagens / expo 98 Lisbon SE office - n.p. / services21 Palacio Sotto Mayor Lisbon SE sevices22 Torre Zen Lisbon S office - n.p. / services23 ABB Sollentuna /W office - n.p.Stockholm24 Arlanda Stockholm N / S / E / W other (airport terminal)25 Sweden WSP Glashuset Stockholm S office - p. / school26 Kista Kista / Stockholm S / W office - n.p.27 Polishuset Stockholm S / W office - n.p.28 Germany IBP VERU Holzkirchen W test facilityNote: p = public; n.p. = non-publicSource: Streicher (2005)ABER_Ch_014/3/074:34 PMPage 8Besides the buildings described above, a special type was covered in the analysis too.In the faade of BiSoP, Baden, the operable windows are bypassing the gap. This seemsto be a good compromise for using the interesting aesthetics of the DSF and at the sametimeavoidmanydisadvantagessuchasoverheating,condensationandsoundtransmission. However, natural ventilation by opening of windows is limited by the heightof the building because of the increasing wind pressure on the faade. In Belgium there is a specific situation concerning the concepts of ventilated doubleskin faades (VDSFs). Indeed, a national project has shown that the majority of VDSFs useanindustrializedfaadeconceptwherethefaadeispartitionedperstoreywithjuxtaposed modules and characterized by a single ventilation mode: the indoor air curtain.The faade is used to extract the air from the room with which it is in contact (indoor aircurtain).Usually,forthemajorityofbuildings,notonlytheVDSFbutalsotheHVACequipment are of the same kind (Figure 1.3). In Portugal DSF buildings are located mainly in Lisbon, where different architects havedesigned several that are high-rise. These are mainly privately owned office buildings, someof them belonging to important Portuguese financial institutions. In fact, DSFs were alreadybeing designed in Portugal in the 1980s (Caixa Geral de Depsitos, Av. da Repblica), andcurrently different typologies coexist in the city of Lisbon. These buildings usually have morethanfivestoreysandthemostcommontypologiesarecorridorfaadesandmulti-storeyfaades. Aesthetics and energy conservation are some of the main reasons that architectsuse to support the use of DSFs. Despite the significant number of DSF buildings in Lisbon,and according to the information gathered, until now no comprehensive energetic, acoustic,lighting and user acceptance study of Portuguese DSFs has been made.In Sweden the interest among architects in applying the technique of double skin glassfaades, mainly in new construction of office buildings, has increased over recent years. SuchbuildingshavebeenbuiltprimarilyintheStockholmarea,forexample,theKistaScienceTower, the ABB-house, the new police house, Glashusett and the Arlanda Terminal F, but thereare also examples in other Scandinavian countries. In total there are about ten modern glazedoffice buildings with DSFs in Sweden. In these cases the purpose of the double skin has beentoreducehighindoortemperatureswithprotectedefficientexteriorsolarshadingduringDouble Skin Faades in European Buildings 9ADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128FIGURE 1.3 The typical Belgium DSF within the multitude of varietiesType of ventilation(1 per faade)MechanicalVentilatedDoubleWindowDSF per storeywith juxtaposedmodulesCorridor DSFper storeyMulti-storeyDSFMulti-storeylouver DSFShaft-boxDSFBuffer zone Air exhaust Air supply OutdoorAirCurtainIndoor AirCurtainVentilation mode( 1 per faade)Hybrid NaturalPartitioning of thecavity(1 per faade)Source: Streicher (2005)ABER_Ch_014/3/074:34 PMPage 9summer, reduce transmission losses during winter, and, in some cases, also to reduce noisefrom motor traffic. The DSF in Scandinavia has rarely been used for ventilation of the buildingbehind. Modern office buildings in Sweden have high energy savings potential and potentialforindoorclimateimprovements.Theymayhavealowerenergyuseforheating,but,bycontrast,theyoftenhaveahigheruseofelectricitythanolderofficebuildings.WhyareofficeswithfullyglazedfaadesbeingbuiltinSweden?Architecturallyanairy,transparentand light building is created, with more access to daylight than in a more traditional officebuilding(Svenssonandqvist,2001).Technicallyitispossibletohaveprotectedexteriormovable efficient solar shading, to reduce noise from motor traffic and to open windows forventilation during part of the year (Carlsson, 2003). Swedish buildings with DSFs share manyof the characteristics of DSFs in Germany, that is, they are mainly for high-profile, high-qualityoffice buildings (new constructions) and are used when building envelopes with transparencyand lightness are wanted and daylight and aesthetics are important.Examples from Germany are two office buildings in Munich: a major public library inUlm in the extraordinary shape of a pyramid, and the VERU test facility at the FraunhoferInstitute for Building Physics in Holzkirchen near Munich. Data for the buildings are basedon the energy performance certification according to the new standard DIN 18599. DuringtheplanningphaseofthelibraryinUlmscientificsupportwasgiven,includingenergyperformance calculations according to the former Wrmeschutzverordnung and thermalsimulations.Detailedenergyconsumptiondataarenotavailableforthelibrary,butthetotalenergyconsumptionlevelsareknown.DatafortheVERUtestfacilityaredetailedandcalculatedwiththeDIN18599.However,thisbuildingisnotoccupiedbyusers,therefore a user investigation is not possible.DSF examples from Greece are three office buildings, a hotel that is under renovationand a retail building that is currently under construction. The majority of the DSF buildingsarelocatedinAthens,apartfromoneofficebuildingthatislocatedinKilkis,anorthernarea ofGreece.DifferentDSFtypologiesareusedinthesebuildings:thecorridortype, the doublewindow,themulti-storeyfaadeandthemulti-storeylouvrefaade.The doublewindowfaadewasusedforacousticreasonsinthehotelbuilding,whichis located in a densely built-up area of central Athens with high traffic and noise levels. Theother types of DSFs were chosen mainly for aesthetics and energy conservation reasons.However,inGreecewheretheclimaticconditionsencouragetheuseofnaturalventilation and necessitate the control of solar gains in order to prevent overheating, thepreferred types of DSF are the multi-storey faade and the multi-storey louvre faade thatcombine external shading systems and natural ventilation.FAADE TYPES IN DIFFERENT CLIMATIC REGIONSAsbuildingswithDSFsaremainlyerectedinthebigcitiesthathaveaspecialcityclimate,similarclimaticconditionsapplyforthebuildingsinallthecountries.Thus,althoughAustriacoversdifferentclimaticregionssuchasthepannonianandalpineclimates, DSFs are concentrated in the capital city of Vienna. However, DSFs can be foundin smaller cities too, for example in Graz, Leoben, Salzburg and Bregenz, but again theseshare similar climatic conditions. Other countries such as Belgium are too small to havedistinctive climatic regions, while in Sweden and Portugal all the researched buildings are10 W. STREICHER et alADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128ABER_Ch_014/3/074:34 PMPage 10situated in the capitals. Therefore, it is not easy to identify special types of DSF specificto a certain region of a country and so climate does not impact on the choice of DSF typeapplied. Even in Germany there is little point in dividing the country into different climateregions as the differences between them would be minor. However, there are of coursesmalldifferencesconcerningsolarradiationandtemperature(forexample,theFreiburgregion and the Rhine area have more sunshine and higher temperatures in summer than,for example, the regions near the North Sea).TostructuretheBESTFAADEresultsaccordingtoclimaticconditions,threemainregions are proposed: the Nordic region, with Sweden as its only representative; the moderate region, with Austria, Belgium, France and Germany; and the Mediterranean region, with Greece and Portugal. Thefollowinganalysistakestheseregionaldivisionsandtheirspecialcircumstancesintoaccount.Forexample,Greeceislocatedinthesouth-easternpartofEuropebetweenthelatitudes of 34 and 42 N, with a meridian extent from 19 to 28 E. The climate in Greece istypicaloftheMediterraneanclimate:mildandrainywinters,relativelywarmanddrysummers and, generally, extended periods of sunshine throughout most of the year. The yearcanbesubdividedintotwomainseasons.First,thecoldandrainyperiodlastsfrommid-October until the end of March. The coldest months are January and February, with a meanminimum temperature of 510C near the coasts, 05C over the mainland, and lower valuesover the northern part of the country. Second is the warm and dry season that lasts from Apriluntil September. During this period the weather is usually stable, the sky is clear, the sun isbright and there is generally no rainfall. The warmest period occurs during the last ten daysof July and the first ten days of August, with a mean maximum temperature of 2935C. FortheclimateofGreece,controlofsolargainsinthebuildingdesignisimportantduringthesummer periods. Therefore DSFs may lead to overheating during the summer months if thereis no appropriate faade design, ventilation technique, building orientation and provision ofshading. The climate of Greece encourages the use of natural ventilation in office buildings;however, over recent decades there has been an increased use of air conditioning due to highambient air temperatures and high internal temperature gains in large office buildings.Many of the above mentioned potential advantages of office buildings with DSFs arelikelytobevalidforSwedenaswell.Inaddition,thereareotherpotentialproblems(Blomsterberg, 2003): During warm summer, spring and autumn days high temperatures in office roomscan occur as a result of window ventilation. The low altitude of the sun results in fairly high cooling demands during spring andautumn. The is a possible risk of high energy use. There is a risk of low daylight levels in the central parts of the building, mainly fordeep buildings. Operation and maintenance costs can be high.Double Skin Faades in European Buildings 11ADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128ABER_Ch_014/3/074:34 PMPage 11ManymodernSwedishofficebuildingshavelargeglazedfaadesandsomehavetheadditionalfaadegivenbyaDSF.ThesimplestandmostcommonsystemsolutionsinSweden entail that the faade is only ventilated to the outside. This usually means that theoffice building behind has a traditional heating, cooling and ventilation system. Windowventilationisusuallynotpossible,apartfromFrenchdoors,whosepurposeistogainaccess to the double skin faade cavity for maintenance.TYPE OF BUILDINGS AND FAADES ANALYSED IN THE BESTFAADE PROJECTMostofthebuildingsanalysedwerenon-publicofficebuildings,followedbypublicschools and services (Figure 1.4). None of the buildings were equipped with a DSF in arenovation process and there were no clear main orientation of the faades, which weremainly an architectural element (Figure 1.5). Most of the faades used natural ventilation12 W. STREICHER et alADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128FIGURE 1.4 Utilization of BESTFAADE buildings0residentialoffice publicoffice non-publicsellingservicesproductionindustryhotelschoolother5 10 15 20 25Source: Streicher (2005)FIGURE 1.5 Implementation and orientation of faades within BESTFAADE0 5 10 15 20 25as part of the new buildingrenovationnorthnorth-easteastsouth-eastsouthsouth-westwestnorth-westSource: Streicher (2005)ABER_Ch_014/3/074:34 PMPage 12and some a hybrid ventilation scheme. The multi-storey approach was mainly used, whileothers adopted the corridor type and juxtaposed modules (Figure 1.6.).EXISTING SIMULATIONS AND MEASUREMENTSIn Austria not many measurements have been done from which data are available. FromBiSoP, Baden, south faade intensive measurement data compared to simulation data areavailable. In this case the aim was to research the physical behaviour of the faade andnot primarily its influence on the rooms behind. FH Kufstein has done some simulationsand measurements as well. From Felbermayr, Salzburg, some single measurement dataareavailable,whileUniqahasdonemuchworkonthisbutithasnotbeenpossibletoobtain those data. In Belgium BBRI has carried out several measurements on DSFs: some in situ, some inoutdoortestcellsandsomeinlaboratories.Differentfieldswereexamined:energy,ventilation, acoustics and daylight. A detailed monitoring of the most common concept ofDSF applied in Belgium was performed in 2005 in order to determine the thermal and solarproperties(inwinterandsummer)ofthiskindoffaade.Someuniversitieshavealso performed measurements in laboratories or in situ. All these measurements have beenrealized at the level of the faade component (and not at the level of the building). BBRI hasalsoperformedsimulationsondifferentkindsofDSF,alsoindifferentfields:energy,acoustics and daylight. In the design phase of a building equipped with a ventilated doublefaade, it is essential to be able to predict the energy performances of the faade in thebuildingfordifferentdesignpossibilitiesofthefaade.Thepossibilityofmodellingthefaade(andthebuilding)withsimulationprogramscanplayanimportantrolefromthatpoint of view and allows the comparison of different possible design concepts. The prediction of the energy performances of a ventilated double faade is a complexmatter.Thethermalprocessandtheairflowprocessinteract.Theseprocessesdependon thegeometric,thermo-physical,opticalandaerodynamicpropertiesofthevariouscomponentsoftheventilateddoublefaade.BBRIhaspublishedadocumentthat explainshowthethermalandsolarperformancesofVDSFsandofbuildingsequippedwiththiskindoffaadecanbepredictedbysimulation.ControlaspectsareDouble Skin Faades in European Buildings 13ADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128FIGURE 1.6 Type of ventilation and partitioning of the gap0 2 4 6 8 10 12 14 16 18 20naturalmechanicalhybridventilated double windowjuxtaposed modulescorridor typeshaft-box faadeothermulti-storey louvre faademulti-storey faadeSource: Streicher (2005)ABER_Ch_014/3/074:34 PMPage 13consideredtoo.Insomecases,measurementsandsimulationshavebeencompared(Flamant et al, 2004).In its analysis, the objectives of the BBRI were: To consider not only the modelling of the VDSF alone, but also the modelling of thewhole building equipped with the faade, the HVAC systems and the control aspects.Simulation programs (only software that is available in the market) are analysed.Studying the interaction between the faade, the building and the installations isimportant for a good assessment of the performances of VDSFs. Until now,practically no research study has assessed the impact of the control systems and theintegration of VDSFs with HVAC systems; To analyse the capability to simulate control systems and control strategies. To assess the various simulation programs based on their modelling possibilities,user-friendliness, advantages, disadvantages and so on. To explain how a VDSF can be modelled with various software. Sometimes, tips areneeded. This is the reason why the knowledge of experts in simulation has beencollected.In Germany DSF is applied mostly to high-rise office buildings. The building owner or userisnormallynotinterestedinpublicizingtheplanninginformationindetail.Technicaljournalslikearchitecturaljournalsoftenshowhigh-qualityphotosofthefaadesanddescribe the usefulness of the faade with many words, but the simulation results and themeasuredenergyconsumptionsoroccurringtemperaturesarerarelypresented.Additionally,detailedmeasurementsaremostlyinitiatedafterproblemsoccurwiththeindoor comfort or high energy consumptions. This leads partly to a bad reputation of DSFsamongspecialistsinthisfield.GoodexamplesofbuildingswithDSFsandlowenergyconsumption as well as good indoor comfort have to be better documented, monitoredin detail and publicized. Simulations need to check if the boundary conditions dependentontheuser,theweather,HVACandsoonarerepresentedinacorrectwaysothattherealityaftertheerectionofthebuildingdoesnotdeviatetoomuchfromthesimulated results.TheexperienceatFraunhofer-IBPwithDSFsincludethefollowingbuildings: Fraunhofer Central Administration, Munich (owner: Fraunhofer Gesellschaft, 2000,simulation); Neubau Katharinenhospital, Stuttgart (owner: city of Stuttgart, 2002, simulation); Neubau Bibliothek Ulm (owner: city of Ulm, 2003/2004, simulation, control strategy); Mnchner Tor, Munich (owner: Mnchner Rck, 2005, energy performancecertificate); Sued 1, Munich (owner: Mnchner Rck, 2005, energy performance certificate); Berlaymont Building, Brussels (owner: European Union, 2005, energy performancecertificate); and VERU test facility for entire building concepts (owner: Fraunhofer-IBP, 2004,measurements, performance assessment calculations).14 W. STREICHER et alADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128ABER_Ch_014/3/074:34 PMPage 14TheonlyknownsimulationinGreecewasmadeforthenewheadquartersbuilding(currentlyunderconstruction)ofALUMILS.A.inKilkisinnorthernGreece,aspartofan internationalarchitecturalcompetitioninwhichthebuildinggotthesecondprizeinthe professionalcategory.ThissimulationfocusedonthecomparisonoftheDSFbeing constructed with a typical single skin faade building, a base case building followingtheGreekbuildingregulations,andatypicalbrickbuilding.Thiscomparisonwasmadeon energyconsumption,lightingneedsindaytime,visualcomfort,shadingflexibilityand thepossibilitiesforviewsfromtheinteriorspacesofthebuildings.Onallaccounts theproposedDSFwasbetterthanthebuildingssimulated,apartfromthe comparisononlightingneedsduringdaytime,wherethesingleskinbuildingbehaved better.Measurements of the environmental performance of the existing Alumil DSF have beencarriedoutbyNKUAwithintheBESTFAADEresearchprogramme.Themeasurementsinclude: dry bulb temperature (C) of external shell, faade gap and internal shell using athermometer; relative humidity (percentage) of external shell, faade gap and internal shellusing a humidity sensor; air change rates (ach) of the faade gap, measured using a tracergas system according to the decay method; wind speeds (m/s) externally and in the faadegapusingahotwireanemometer;globalsolarradiation(W/m2)perpendiculartotheexternal shell, faade gap and internal shell, measured using pyranometers; and levels ofdaylighting(lux)externally,inthefaadegap,internallyandontasklevels,evaluatedbyluxometer.Additionally,theenergy(electricity,airconditioning,heatpumps,lighting)andenvironmentalperformance(thermalcomfort,temperaturesandrelativehumidity)oftheAVAXS.A.headquartersofficebuildinghavebeenmonitoredbyanelectronicdigitalsystemforcentralmonitoringandcontrol(buildingmanagementsystem,BMS).Themonitoring was carried out for the period 1 July 2000 to 30 June 2001.DespitetheinterestthatPortuguesearchitectsshowtowardsDSFtechnology,untilrecentlythisinterestwasnotaccompaniedbythePortuguesescientificenergy-relatedcommunity. The situation was reversed in 2005 with the inclusion of Portuguese researchinstitutions in scientific projects related to the evaluation of DSF technology (for example,through BESTFAADE). Doctorate and masters students and researchers from ISQ, LNECandINETI(Portugueseresearchinstitutions)arecurrentlystudyingdifferentaspectsofPortugueseDSFbuildings,boththroughtheuseofsimulationtools(Energy-PlusandDOE-2),laboratorytests(airflowfielddetails)andgapandindoormonitoring(acoustic,thermal, lighting and energy parameters). One DSF building is currently being thoroughlymonitoredandmorethanfivescientificpaperswheresubmittedforpresentationatinternational conferences. Recently, in the context of the design of a new DSF building tobe located in the Expo98 area in Lisbon, a prototype of a DSF as been build and monitoredfor thermal conditions in the air gap.In Sweden simulations have been made for energy use and indoor climate of buildingswithDSF,usingmulticelldynamicsimulationtools.However,thereisnotyetanycommercialsimulationtoolavailablethatactuallysimulatestheDSF.Knowledgeisinsufficient on the actual energy performance, indoor climate performance and so forth ofbuildings with DSFs, partly due to the fact that most of these buildings have only been inoperation for a couple of years.Double Skin Faades in European Buildings 15ADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128ABER_Ch_014/3/074:34 PMPage 15InmanyprojectswithDSFssimulationsoftemperatures,airandenergyflowshavebeencarriedoutbeforeandduringthedesign,withmoreorlesssuccess.Oftenthesimulations have deviated from the result in the finished building. This reflects difficultiesindefiningandaccuratelydeterminingtheboundaryconditions.Tosucceedwithcalculations not only good experience of the used simulation models is required, but alsogoodknowledgeofthermodynamics,fluiddynamicsandbuildingphysics,andgeneralshrewdnessandexperienceofbuildingservicesengineering.Increasedknowledgeandthe improvement of simulation and calculation methods are needed. HVAC SYSTEMS, THERMAL BEHAVIOUR, INDOOR AIR QUALITY,COMFORT AND USER ACCEPTANCEThe main heating delivery systems found in the buildings analysed for the BESTFAADEprojectwereairheatingfollowedbyradiators,themainheatsourcesweredistrictheating,electricityandgasoroil(Figure1.7).Forspacecooling,coldairdistribution16 W. STREICHER et alADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128FIGURE 1.7 Types of room heating device and energy source used in BESTFAADE buildings0 5 10 15 20 25gas / oilelectricitybiomasssolardistrict heatingotheruser influenceactivated concrete corehot air heatingradiatoroverhead radiation heatingfloor heatingunder floor convectoryes noSource: Streicher (2005)FIGURE 1.8 Types of room cooling device and energy source used in BESTFAADE buildingsyes nogas / oilelectricitybiomasssolardistrict heatingotheruser influenceactivated concrete corecold air coolingno cooling systemoverhead radiation coolingfloor coolingunder floor convector0 2 4 8 10 6 12 14 16 18Source: Streicher (2005)ABER_Ch_014/3/074:34 PMPage 16dominatesandispartlyassistedbyotherapplianceslikecoolingceilings,floorcoolingand activated concrete cooling (Figure 1.8).Ventilation is mainly performed by mechanical ventilation, but also windows into thegapandbypassingthegaphavebeenrealized(Figure1.9).Mostofthefaadeshavebottom and top openings in the outer shell of the faade that can be closed during winterand opened in summer (Figure 1.10). For the inner shell only half of the analysed faadeshave openings (mainly windows, Figure 1.11). If present, they are, of course, closable.The airflow in the faade is mainly vertical, but also diagonal and horizontal flows havebeenbuilt.Whereasmostofthefaadesallowanairflowinsummer(toavoidtoohightemperatures in the gap), only about half of the faades close in winter to use the air gapas unheated sun space (Figure 1.12). The thermal comfort encountered in a building equipped with a DSF can be improvedcomparedtoasingleglazedfaade,especiallyduringwinterwherethetemperatureofthe inner glazing will usually be higher than a traditional faade. That reduces the thermalDouble Skin Faades in European Buildings 17ADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128FIGURE 1.9 Ventilation and air conditioning of BESTFAADE buildingsyesno0 5 10 15 20 25 30windows into the gapwindows bypassing the gapmechanical ventilationhumidifydehumidifypreheatprecooluser influenceSource: Streicher (2005)FIGURE 1.10 Ventilation openings in outer shell of analysed faades0 2 4 6 8 10 12 14 16 18supply airexhaust airwindowsshutterssegmentsgridsotherclosableyes noSource: Streicher (2005)ABER_Ch_014/3/074:34 PMPage 17radiation of the cold surface of the glazing. In summer, the air temperature in the cavity ofthe DSF can be high (>50C), depending on the type of DSF. The temperature of the innerglazingcanalsoreachhighlevels(>30C),whichcancreatethermaldiscomfortandoverheating (or higher energy consumption for cooling). A proper choice of the shadingdevice and of the air ventilation rate is important.For some types of DSF in Belgium, there is no direct influence of the faade on the airquality in the adjacent room since the air of the room is extracted via the faade (no air supply).18 W. STREICHER et alADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128FIGURE 1.11 Ventilation openings in inner shell of analysed faadesyes no0 2 4 8 10 6 12 14 16supply airexhaust airwindowsshutterssegmentsgridsotherclosableSource: Streicher (2005)FIGURE 1.12 Airflow in the gap in summer (above) and in winter (below)0 2 4 6 8 10 12 16 14 18summer/verticaldiagonalhorizontalnonesummer/verticaldiagonalhorizontalnone0 2 4 6 8 10 12Source: Streicher (2005)ABER_Ch_014/3/074:34 PMPage 18In some published articles on German DSF buildings, the applied technology leads tohigh temperatures in the faade gap in summer that partly cause overheating problems inthe adjacent rooms. This is mostly solved by big air-conditioning plants and therefore highoperationcosts.However,somebuildingsshowthatwithgoodplanningDSFsdonotnecessarilyleadtocriticalthermalsituationsandcomfortproblems.InGermanyDSFplanning has to be based on the summer conditions. First, the overheating problem hastobesolved,andsecond,thefaadeshouldbeadaptedtopossiblegainsduringthewinter. The indoor air quality may be influenced by the faade in several ways if there areopenings from the rooms to the faade gap: positively, because in high-rise office buildings natural or hybrid ventilation might notbe possible without the DSF; positively, if the air taken from the gap into the rooms in winter is warmer than theroom temperature (possibility of reduction of the heating demand); negatively, as the faade may lead to bad air quality being transferred from one roomto the other (for example if there are smokers); and negatively, if the air taken from the gap into the rooms in summer is hotter than theroom temperature (increase of cooling demand).User acceptance is dependent on these influences (thermal behaviour, indoor air qualityand comfort) but also on the possibility to control the environment as well as other thingssuch as acoustics or aesthetics.Published data on thermal behaviour, indoor air quality and comfort of DSF buildingsinGreeceapplytotheAVAXheadquartersofficesthatweremonitoredviathebuildingmanagement system. Additionally, questionnaires on thermal comfort were distributed tousers. The results show that: Due to the design, orientation and construction of the faade, good visual comfortwas achieved in the office areas provided mainly by natural daylight. Thermal comfort was mainly described as neutral with little request for changes. Energy consumption was reduced to almost half compared to similar buildings withconventional lighting and air-conditioning systems.Users acceptance of DSFs was evaluated within the BESTFAADE project. Currently DSFexamples have no reputation in Greece because of their limited application. Initial resultsof the analysis show that the users are positive about DSF systems if the faade designdoes not lead to overheating.Duetoalackofscientificandfieldstudiesitisdifficulttoreportonthermalbehaviour, indoor climate, comfort and user acceptance of DSF buildings in Portugal. It isalsodifficulttojudgewhetherornotDSFsperformbetterwhencomparedtosingle-glazedfaades.Apreliminaryanalysisofsomeoftheexistingbuildings(typeofglazing,shading)suggeststhatproblemsofoverheatingcouldoccur.Informationgatheredfromconversationswitharchitectsandmaintenancepersonnelalsopointto this possibilityorreality.StudiescurrentlyongoinginPortugueseDSFbuildingsDouble Skin Faades in European Buildings 19ADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128ABER_Ch_014/3/074:34 PMPage 19(within theBESTFAADEproject,forexample)willcontributetoclarifytheseveryimportant aspects.The long, cold and dark winters in Sweden can cause thermal comfort problems. Thelow altitudes of the sun can result in fairly high cooling demand during spring and autumn.The visual comfort can be problematic due to glare in the boundary zone. For deep buildings,the daylight level can be low in the core of a building, although the faade is fully glazed. Obviouslythereisanuncertaintyinthebuildingtradeastothedesignofbuildingswith highly glazed faades and how to calculate the use of energy, the comfort and theinfluence on these buildings of different technical solutions.ENERGY DEMAND AND CONSUMPTIONThereareveryfewdataavailableforenergydemandandconsumptioninbuildingsequipped with DSFs. There are publications showing very high energy consumption levelsin some well-known DSF office towers in Germany. Two of the projects analysed withinBESTFAADE include the comparison between the final energy demand calculated withDINV18599accordingtothenewEnergyPerformanceofBuildingsDirective(EPBD)requirementsandthefinalenergyconsumption.Inthesecasesbothcalculationofdemands and monitoring of consumption by the energy provider resulted in values in therange of usual office buildings or better.TheresultsregardingenergyconsumptionofDSFbuildingsinGreecerefertotheAVAX S. A. headquarter offices. The results show that the faade design, in conjunctionwith the use of natural ventilation, night mechanical cooling and energy efficient lighting,results in significant energy savings and operational cost.ThelevelofknowledgeonDSFsamongmostscientists,builders,developers,consulting engineers and architects in Sweden is fairly limited, especially concerning theactualenergyandindoorclimateperformanceofthebuildingbehindthefaade.Theexception is some major property owners/developers, engineers and architects. Portugalis also in a similar situation.CONTROL STRATEGIESInBelgiumcontrolsystemsandstrategieswerestudiedduringthenationalprojectonDSFsmanagedbyBBRI.ThisstudyshowedthatthecontrolsystemsandstrategiesappliedinbuildingsequippedwithDSFsare,mostofthetime,verysimilartothoseappliedforsingleglazedbuildings.Anefficientoperationofthefaadeisonlypossiblewhen there is efficient control of the motorized components that are integrated in the DSF.This can be realized via the building management system (BMS), which allows an optimaloperation of the different systems of the building. In Belgium the use of BMS is currentlynotgeneralized.Veryoften,nomajordifferencesexistinthecontrolstrategyappliedbetween a traditional building and a building equipped with DSF. Control strategies for thefaade and/or the building and plants behind the faade are variant and very dependentonthetypeoffaade(self-operating,passiveoractivelyinfluencingtheclimateinthebuilding).Thefaadecontrolmayoperatetheopeningofthefaade(ventilationofthegap),maysupporttheactiveventilationinthegap,andmaycontrolsolarshadinganddaylighting.20 W. STREICHER et alADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128ABER_Ch_014/3/074:34 PMPage 20ThecontrolstrategyofthebuildingforHVACandlightingshouldbeadapted(orifpossible linked) to the control of the faade and to the user boundary conditions. In high-rise office buildings the controls are mostly realized by the building energy managementsystem (BEMS), which can also monitor the energy consumption of the building. Use of aBEMS makes it easier to refine the control strategy towards the most suitable and energyefficient solution and discover unnecessary energy consumption because of false controlstrategies or mistakes in the programming. A commissioning of the building and the plantsis indispensable. In Portugal the more recent DSF buildings include faade-related controlstrategies, mainly for cooling and lighting systems. Control is automatic through the BEMS.TheshadingsystemthatismostlyusedinthefaadesanalysedinBESTFAADEisvenetian blinds, with canvas screens used to a lesser extent. The control systems are nearlyequallydistributedamongmanualcontrol,automaticcontrolwithmanualoverrideandautomatic control without manual override. Daylight control is used only rarely.INTEGRATED BUILDING TECHNOLOGYDSFs allow, to a certain extent, the integration of technical systems for the conditioningoftherooms.Localair-conditioningsystemsdisburdentheinstallationductsinthebuildingcore.WithnewerprojectsDSFdevelopmentshavebeenrealizedthatinclude,apart from the room conditioning, lighting systems and PV elements within the faade.InBelgium,usually,forthemajorityofbuildingsequippedwithDSFs,thewholeconcept including the faade is similar to the HVAC system. The faade is mechanicallyventilated with cooling beams or cooling ceilings with activated concrete. The room air,whichisextractedviathedoublefaade,isreturnedviaventilationductstotheHVACsystem.Thecontroloftheshadingdevicesituatedinthefaadecavitycanbedonemanually or centralized at the level of the room or at the level of the building via the BMS.Integrated building technology exists in DSF buildings in Portugal. The oldest of thesebuildings, designed in the 1980s, already included a system to recover the heated gap airand use it to heat offices located far from the DSF. Figure 1.13 shows elements of buildingtechnologyintegratedinthefaadesanalysed.Fireprotectionandactivesolarsystemswereusedinaboutonethirdofthefaades.OnlyafewbuildingsincludePV,soundabsorbers or pluvial protection devices. COST (INVESTMENT, MAINTENANCE AND OPERATION)In a national Belgian project on DSFs, BBRI did not carry out a very detailed analysis of thecost of the buildings equipped with DSFs. Nevertheless, the different elements having animpact on the cost of DSFs were analysed. The initial investment in the DSF bears an extracost that can be very high for some specific types of DSF. For the most commonly usedDSF in Belgium (mechanical ventilated faade with juxtaposed modules), total cost rangesfrom A500700/m2, including solar shading. With some types of DSF, heating appliancescan be avoided or the capacity of the heating appliances can be reduced, both of whichreduce the installation cost. The impact of a DSF on the dimensioning and/or the choiceofthecoolingsystemsdependsonthesolarperformances(g-value)ofthefaade.The changeinoperationcostisproportionaltoenergy(heatingandcooling)reductionor increase for the whole building equipped with a DSF compared to a traditional building. Double Skin Faades in European Buildings 21ADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128ABER_Ch_014/3/074:34 PMPage 21The maintenance cost specific to the glass skins is of course higher because of thepresence of four surfaces to be cleaned. The source of the ventilation air passing throughthe cavity also plays a role: more cleaning is needed in the case of a cavity ventilated withoutsideair.Theenvironment(pollutionornopollution)alsoinfluencesthefrequencyofcleaning. The shading device situated in the cavity of a DSF is protected against the windand the rain, which is favourable compared to external shading devices.As with energy consumption, the building owner and/or users in Germany do not aimatdisseminatingthecostfortheerectionoftheirbuildings,withorwithoutDSFs.Construction management companies and faade manufacturers should have more insightintotheinvestmentcost.InthecaseoftheGermanBESTFAADEproject,participantFraunhofer Institute for Building Physics is usually not party to the financial side of projects,butdealswithenergyefficiencyandenergyeconomy.ADSFmeanstwo faades(innerand outer shell, which does not necessarily have to add up to the price of two faades, butwill lead to a higher cost than most of the usual faades with only one skin). Additionally,theDSFsaremainlyglazedonbothshells;glazingand especiallythenecessarysafetyglass, is more expensive than insulated panels. The investment cost of the DSF applied attheVERUtestfacilityamountedtoA1255/m2of faadearea(thoughitshouldbementioned that this faade has a very small total area of 40m2). Figures1.14and1.15showabsoluteandadditionalcoststhatwerecollectedfromdifferentpublicationsonDSFs.Duetothewiderangeoftechnicalpossibilitiesandeconomic boundary conditions, a wide range of costs is reported.For Sweden up-to-date estimated investment costs for the new WSP office building inMalm are shown. The builder/developer is Midroc Projects, with costs according to WSPand Schco. Approximate investment costs for different glazed faade alternatives are: single skin faade without exterior solar shading, A370/m2; single skin faade with fixed exterior solar shading (catwalk not included, simplecontrol of solar shading included), A580/m2;22 W. STREICHER et alADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128FIGURE 1.13 Integration of different devices into the faadesyes no0 5 10 15 20 25 30sound absorberfire protectionacitve solar systemphotovoltaicpluvial protection devicesradar damping systemotherSource: Streicher (2005)ABER_Ch_014/3/074:34 PMPage 22 single skin faade including daylight redirection (catwalk not included, simple controlof solar shading included), A680790/m2; DSF, including venetian blinds, such as the Kista Science Tower, A9201000/m2; DSF box window type (cavity width 0.2m) with venetian blinds, A560/m2; DSF box window type (cavity width 0.2m) with venetian blinds, including daylightredirection, A610/m2.Double Skin Faades in European Buildings 23ADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128FIGURE 1.14 Cost of DSFs compared to conventional faadesNote: The hatched areas show the range of cost mentioned in Blum (1998), Daniels (1997), Kornadt (1999), Schuler (2003) and own data. Source: Streicher (2005)FIGURE 1.15 Additional cost of DSFs according to different authorsNote: The hatched areas show the range of cost mentioned in Blum (1998), Kallinich (1994), Kornadt (1999), Oesterle (2003) and Schuler(2003).Source: Streicher (2005)ABER_Ch_014/22/0711:15 AMPage 23RESOURCE CONSERVATION AND ENVIRONMENTAL IMPACTTheenvironmentalimpactofaDSFisinfluencedbytwofactors:theadditionalenergyneeded to build the DSF (namely, in the second glass skin compared to a single glazedfaade), and the reduction/increase of the energy consumption of the building. Very fewdata are available on this.Theenvironmentalimpactcanbedescribedintwoways:energyconsumptionforthe operation of the building and the embodied energy used for the fabrication of the faade.Here again, two levels of faade will cause more embodied energy than one level. Besides theglazing,theDSFusuallyconsistsmainlyofaluminiumframes.Aluminiumisamaterialthatconsumes a lot of embodied energy during the fabrication. However, the manufacturers havesearched for solutions to decrease incorporated embodied energy in their product, includingproduction of aluminium in Norway (with hybrid power) and a high recycling rate of the material.COMPARISON TO CONVENTIONAL GLASS FAADESThe performance of DSFs in Austria varies intensely from buildings with good reputations,such as the Andromeda Tower, Vienna, to faades with severe problems, for example newandretrofittedbuildingsinViennawhereglasspanesfellfromtheDSFs.Thereare,however, conventional glass faades that have poor energy performance. In some casesDSFs can be a good choice for the retrofitting of buildings constructed in the 1960s and1970s. Advantages may be good heat storage capacity of thermal mass behind the glassfaade, new aesthetics and noise reduction.DifferentcriteriaplayaroleinthecomparisonbetweenaDSFandaCGF.Theevaluation depends on the type of DSF: Energy consumption for heating few data are available. A detailed analysis must beperformed in order to evaluate the possible energy savings. The DSF with juxtaposedmodules is usually characterized by better thermal performances in winter than atraditional faade. Energy consumption for cooling few data are available. A detailed analysis mustbe performed in order to evaluate the possible energy savings. For the DSF withjuxtaposed modules the cooling consumption can in some cases be higher than for a traditional faade equipped with external shading devices. Acoustics the acoustical insulation (against external noise) of a DSF is better.However, for specific types of DSF, problems of indirect transmission of soundthrough the cavity can occur (telephony effect). Daylight good penetration of daylight in buildings equipped with DSFs. This is alsopossible with single glazed faades. Fire certain types of DSF can be a problem concerning fire risk. The second skindoes not allow smoke to escape. Shading device a DSF allows the utilization of the shading device in all weatherconditions due to the protection of the shading device situated in the faade cavity. Opening of windows this is possible with certain types of DSF to allow the naturalventilation of offices, even for high buildings. Image a high-tech image plays a role in the application of DSFs. 24 W. STREICHER et alADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128ABER_Ch_014/3/074:34 PMPage 24Below is a more detailed comparison of DSFs with CGFs, though it should be mentionedthat DSFs may offer possibilities that cannot be realized with most conventional faades,for example natural or hybrid ventilation in high-rise buildings.The maintenance of the faade consists of cleaning and repair. Four surfaces have tobecleaned(insteadoftwo):theinnerandoutersideoftheexternalfaade,aswellasinnerandoutersideoftheinternalfaade.InwideDSFs(>60cm),forthetwomiddlesurfacesaccessiblegridsareusuallypartofthefaadegap.Thisfacilitatesthework.However, additional cleaning costs have to be taken into account with DSFs. According totheBESTFAADEquestionnaire,theoutersurfaceismainlycleanedwithmovingplatforms or cradles, whereas the inner glazing is mainly cleaned from the corridor. AlsotwoshellsmighthavemoredefectsforrepaircomparedtoCGFs.Bycontrast,aDSFofferssomeadvantageslikeaprotectedshadingsysteminthegap,whichwillhavedefects less often.The operational cost (energy cost + maintenance cost) cannot be entirely assigned tothefaadesystembuttothebuildingasawhole.Asmentionedabove,theenergyconsumption of a building can be negatively influenced by bad planning of the DSF, keptatthesameleveloralsoslightlypositivelyinfluencedbyaDSF.Accordinglytheenergyconsumption cost will increase, stay the same or decrease.ConsideringthesignificantnumberofDSFbuildingsinLisbon,DSFtechnologyisacceptedamongPortuguesearchitectsandpromoters.Thecombinationoftheaestheticalappearancethatthistechnologyenablesanditsenvironmentalattributes,oftenmentionedinNorthernandCentralEuropeanspecializedliterature,canbeoneofthe main reasons for its use instead of single glazed faades.INTEGRATION OF RENEWABLE ENERGY SOURCES INTO DSFsTheonlycaseknownamongtheresearchedAustrianDSFsistheuseoftheconcreteareasbehindthesouth-facingglassfaadeassolarcollectorsinBiSoP,Baden,whichshouldsupplyhotwaterradiatorsinthenorth-facingfaadetoreducetemperaturespread. For Belgium, Greece and Portugal no applications are known.SomeDSFsincludephotovoltaicapplications.Theelectricalenergygeneratedcaneitherbefedintothegrid(inGermanywithhighlysubsidizedprices)orusedinthebuildingitself.WindenergyandsolarthermalcannoteasilybelinkedwithDSFs,but ofcoursecanbeanadditionalfeatureofthebuilding.Otherrenewableenergieslike heatpumps, use of geothermal energy, wood or similar renewable fuels can be integrated intothe building, partly also for preheating or precooling of the air of the building and maybealso inside the DSF gap, but they are not specifically coupled to the DSF concept.NON-ENERGY RELATED ISSUES: ACOUSTICS, AESTHETICS, FIRE PROTECTION, MOISTURE, CORROSION, DURABILITY,MAINTENANCE AND REPAIRTheseissuesareoftenmoreimportantforuseracceptancethanenergy-relatedperformance because a buildings energy consumption rarely affected is users directly.AcousticscanbeoneofthemainreasonstoapplyDSFs,forexamplewithtrafficnoise (control room of the fire brigade in Graz, Austria, Schubertstrasse). In many casesDouble Skin Faades in European Buildings 25ADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128ABER_Ch_014/3/074:34 PMPage 25DSFscanreducesoundtransmissionfromtheoutsideduetotheadditionalshell.However,dependingonthetypeofDSF,problemsofnoisetransmissionfromroomtoroom by the gap can occur. This can be reduced by choosing the appropriate partitioningsystem or by the implementation of acoustical absorbers in the gap.Aesthetics are often the main aspect for the application of DSFs. They give depth anda kind of crystal image to the faade.Fire protection is a serious issue with DSFs. In the case of fire, fire brigades have todestroy two shells to be able to help the buildings users, also the flashover of a fire fromone storey to the next can be facilitated by DSFs depending on the partitioning system.Thefaademanufacturershavefoundsolutionsforthesecondproblemand,indeed,whentheDSFgapisseparatedbetweeneachstoreyofthebuilding,theproblemofflashoverissmallerthaninconventionalfaades.SometypesofDSFs,suchasmulti-storey DSFs, must not be applied to high buildings.Depending on the ventilation technology, sometimes problems with condensation arereportedwhenwarmandwetexhaustairisventilatedintothegapandmeetsthecoldinnersurfaceoftheouterglasspane(forexample,FHKufstein).DurabilityisalsounprovenduetothefactthatmostDSFsareprototypes,especiallywithpanefixtures(though the same problems may also apply to CGFs) and mechanically driven shutters orlamellae. Since DSFs are a relatively new development, there has been no scientific in-situlong-termanalysisofalarge-scalegroupoffaades.However,problemswiththedurability of DSFs are unknown to date.As mentioned above, the maintenance of the faade consists of cleaning and repairand DSFs generally incur higher cleaning costs. They may also result in higher repair coststhanCGFs,butthisdependsontheamountandtypeoffaadefixtures.However,because shading systems are protected they are less likely to need repair.CONCLUSION TheBESTFAADEprojectstudied28faadesofdifferentbuildingsinseveralpartnercountries by means of a standardized questionnaire. The questionnaire asked for data onlocation, information about the building and the faade, construction and route of airflowin the faade, as well as maintenance and cost. Analysis of the findings took account of the aspects and types of faade in differentcountries,DSFsindifferentclimaticregionsofEurope,existingsimulationsandmeasurements,thermalbehaviour,indoorairquality,comfort,useracceptance,energydemandandconsumptions,controlstrategies,integratedbuildingtechnology,cost(investment,maintenanceandoperation),resourceconservation,environmentalimpact,comparisontoCGFs,integrationofrenewableenergysources,andthenon-energyrelatedissuesofacoustics,aesthetics,fireprotection,moisture,corrosion,durability,maintenance and repair. Mostofthebuildingsstudiedwereoffices,thoughsomeschoolsandservicebuildingswerealsoexamined.Nearlyallofthebuildingshadmechanicalventilationsystemsandbothheatingandcoolingwereperformedmostlybyairheating/coolingsystems.Thefaadesweremainlymulti-storeyandcorridortypes,whileinBelgium26 W. STREICHER et alADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128ABER_Ch_014/3/074:34 PMPage 26juxtaposedmodulesarefrequentlyused.Thefaadegapsweremostlynaturallyventilated (except for Belgium, where the indoor air was led by mechanical ventilation viathe gap to the centralized air handling unit). Shading was performed mainly with venetianblinds located in the gap. The cleaning of the outer shell was done via a cradle or a liftingplatform,whiletheglazingofthegapwasmainlycleanedfromthegaporfromtheinterior. Unfortunately, little data on energy demand and temperatures in the gap and therooms behind the DSFs were available.The cost of DSFs were found to be 2080 per cent higher than CGFs and 100150 percenthigherthanopaquefaadeswithwindows.Thereforetherehavetobesignificantbenefits in HVAC system costs or the operating costs of DSFs to make DSFs them moreattractive than conventional faades. AUTHOR CONTACT DETAILSWolfgang Streicher, Institute of Thermal Engineering (IWT), Graz University of Technology, AustriaRichard Heimrath, Institute of Thermal Engineering (IWT), Graz University of Technology, AustriaHerwig Hengsberger, Institute of Thermal Engineering (IWT), Graz University of Technology, AustriaThomas Mach, Institute of Thermal Engineering (IWT), Graz University of Technology, AustriaReinhard Waldner, MCE Anlagenbau Austria Gmbh & Co, Vienna, AustriaGilles Flamant, Belgian Building Research Institute (BBRI), Belgium Xavier Loncour, Belgian Building Research Institute (BBRI), BelgiumGrard Guarracino, Ecole Nationale des Travaux Publics de lEtat (LASH-DGCB), FranceHans Erhorn, Fraunhofer Institute for Building Physics (FHG-IBP), Stuttgart, GermanyHeike Erhorn-Kluttig, Fraunhofer Institute for Building Physics (FHG-IBP), Stuttgart, GermanyMat Santamouris, University of Athens, Group of Building Environmental Studies (NKUA), Greece Ifigenia Farou, University of Athens, Group of Building Environmental Studies (NKUA), Greece S. Zerefos, University of Athens, Group of Building Environmental Studies (NKUA), GreeceM. Assimakopoulos, University of Athens, Group of Building Environmental Studies (NKUA), GreeceRogrio Duarte, ISQ-Instituto de Soldadura e Qualidade, Porto Salvo, Portugalke Blomsterberg, University of Lund (ULUND), Energy and Building Design, SKANSKA Teknik AB, WSPSverige AB Sweden Lars Sjberg, University of Lund (ULUND), Energy and Building Design, SKANSKA Teknik AB, WSP Sverige AB Sweden Christer Blomquist, University of Lund (ULUND), Energy and Building Design, SKANSKA Teknik AB, WSP SverigeAB SwedenACKNOWLEDGEMENTSWith the support of Intelligent Energy Europe (EIE/04/135/S07.38652).The sole responsibility for the content of this report lies with the authors. It does notrepresenttheopinionoftheEuropeanCommunities.TheEuropeanCommissionisnotresponsible for any use that may be made of the information contained therein.Double Skin Faades in European Buildings 27ADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128ABER_Ch_014/3/074:34 PMPage 27REFERENCES BBRI (2004) Ventilated double faades: Classification and illustration of faade concepts, Belgian Building Research Institute,Department of Building Physics, Indoor Climate and Building Services, Brussels, BelgiumBlomsterberg, . (2003) Project description, glazed office buildings: Energy and indoor climate, Lund University, Sweden,www.ebd.lth.seBlum, H. J. (1998) Das innovative Raumklimakonzept, Bauphysik, vol 20, Heft 3, pp8186Carlsson, P.-O. (2003) Glazed Faades Double Skin Faades, Arkus, Stockholm (in Swedish)Crespo, A. M. L (1999) 3x2: Three Takes on Double Skins, Harvard University, Cambridge, MADaniels, K. (1997) The Technology of Ecological Building: Basic Principles and Measures, Examples and Ideas, BirkhuserVerlag, BaselFlamant, G., Heijmans, N. and Guiot, E. (2004) Ventilated double faades: Determination of the energy performances ofventilated double faades by the use of simulation integrating the control aspects Modelling aspects and assessmentof the applicability of several simulation software, Belgian Building Research Institute, Department Building Physics,Indoor Climate and Building Services, Brussels, BelgiumHarrison, K. and Meyer-Boake, T. (2003) The Tectonics of the Environmental Skin, University of Waterloo, School ofArchitecture, Ontario, CanadaKallinich, D. (1994) Doppelfassaden, Beratende Ingenieure, vol 9, September, pp3645Kornadt, O. (1999) Doppelfassaden: Nutzen und Kosten, Bauphysik, vol 21, pp1019Le Corbusier, C. E. J. (1964) Feststellungen zu Architektur und Stdtebau, Ullstein, Berlin, Frankfurt and Vienna Neubert, S.(1999) Doppelfassaden Ein Beitrag zur Nachhaltigkeit?, Ecole Polytechnique Federale de Lausanne, Lausanne Oesterle, E. (2003) Doppelfassaden - Mglichkeiten und Grenzen der zweiten Gebudehlle, CCI FachtagungDoppelfassaden, Karlsruhe, 27 NovemberPoirazis, H. (2004) Double Skin Faades for Office Buildings Literature Review, Division of Energy and Building Design,Department of Construction and Architecture, Lund Institute of Technology, Report EBD-R04/3, 2004, Lund University,LundSaelens, D. (2002) Energy performance assessment of single storey multiple-skin faades, dissertation, KatholiekeUniversiteit Leuven, Faculteit Toegepaste Wetenschappen, Arenbergkasteel, B-3001, Catholic University of Leuven,Leuven Schuler, M. (2003) Ausgefhrte Doppelfassaden mit minimierter Gebudetechnik, CCI Fachtagung Doppelfassaden,Karlsruhe, 27 November 2003Streicher, W. (ed) (2005) WP 1 Report State of the Art, BESTFAADE, Best Practice for Double Skin Faades,EIE/04/135/S07.38652Svensson, A. and qvist, P. (2001) Double skin glazed faades: Image or a step towards a sustainable society?, Arkus,Stockholm (in Swedish)28 W. STREICHER et alADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 128ABER_Ch_014/3/074:34 PMPage 28 Keywords energy management; indoor environment; fuzzy controller; thermal comfort; visual comfort;indoor air qualityINTRODUCTIONArtificialintelligence(AI)isdefinedasintelligenceexhibitedbyanartificialentity.AIgenerallyassumesthepresenceofcomputers.Neuralnetworks,geneticprogramming,fuzzylogic,computervision,heuristicsearch,Bayesnetworks,planning,languageunderstanding and combinations any of the above are AIs technologies (Nilsson, 1998).AI in buildings technology has been investigated during recent decades. Modern controlsystems provide optimized operation of the energy systems while satisfying indoor comfort.RecenttechnologicaldevelopmentsbasedonAItechniquesofferseveraladvantagescompared with the classical control systems. The use of artificial neural networks (ANNs) invarious applications related to energy management has been growing significantly over theyears(Bellas-Vellidisetal,1998).Currentapplicationsarerelatedtoenergydemandforecasting and to HVAC systems of buildings (Curtiss et al, 1993; Kreider, 1995; Huang andLam, 1997; Khotazad et al, 1997; Han et al, 1997; Karatasou et al, 2006). The results haverevealedthepotentialusefulnessoftheneuralnetworksfortheenergymanagementofhousesandbuildings.Evolutionarycomputing,namely,geneticalgorithms(GA)areADVANCES IN BUILDING ENERGY RESEARCH 2007 VOLUME 1 PAGES 2954AbstractAreviewoffuzzylogicapplicationstobuildingsresearchisthetopicofthispaper.Emphasisisgiventotheapplicationsthatdealwiththeregulationandmodellingofindoor thermal comfort, visual comfort and indoor air quality. The improvement of indoorcomfortwithsimultaneousenergyconservationisconsidered.Heating,ventilationandair-conditioning (HVAC) systems operation, fault diagnosis and their modelling by fuzzylogicforpredictionoftheirbehaviourisalsoinvestigated.Significantattentionisprovidedtotheregulationoftheindoorenvironmentbytakingintoaccountthecombining effect of all comfort aspects. 2Artificial Intelligence in Buildings:A Review of the Applicationof Fuzzy Logic D. KolokotsaABER_CH_024/4/073:33 PMPage 29employedinbuildingssincetheyhaveprovedtoberobustandefficientinfindingnear-optimal solutions in complex problem spaces (Wright et al, 2002; Kolokotsa et al, 2003). Fuzzylogic(Figure2.1)wasintroducedbyZadeh(1973)asamathematicalwaytorepresent ambiguity and vaguen