ACTIEVE EN INTERACTIEVE DUBBELSCHALIGE GLASGEVELS: TOP OF FLOP?

8/7/2019 ACTIEVE EN INTERACTIEVE DUBBELSCHALIGE GLASGEVELS: TOP OF FLOP?

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Copyright:

Teksten/bewerking/en lay-outUitgave:

2004 Niets ui t deze uitgave mag worden verveelvoudigd, opgeslagen ofopenbaar gemaakt, in enige vorm of enige wijze, hetzij elektronisch,mechanisch , door fotokopien, opnamen, of op enige andere manier, zondervoorafgaande schriftelijke toestemming van de betreffende auteurs .

Conny van den Broek

TU-Delft, Faculteit Bouwkunde,Leerstoel Productontwikkeling,Dr. Ing. Just Renckens

CIP-GEGEVENS KONINKLIJKE BIBLIOTHEEK, DEN HAAGRenckens, J .ACTIEVE EN INTERACTIEVE DUBBELSCHALIGE GLASGEVELS: TOP OF FLOP?Faculteit Bouwkunde.ISBN 90-5269-312-9 10 mei 2004 geb.Trefw:Gevels/Glasgevels/FaadesITweedehu idgevelsNliesgevels/Second Skin/Modem FaadeslDouble layer Glass Faades .


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Inhoudsopgave

IntroductionDr. Ing. Just Renekens

Double Ventilated Glass Faades -Acoustical performancesM. Blaseo

Symbiosis of Faade and Climate InstallationsA.H.C. van Paassen, WJ. Stee

Het belang van drukvereffening bij dubbelfaadesProf ir Nieo Hendriks

Operationele prestaties van dubbele gevels alsontwerpopgaveDr. Ing.Just Renekens

Available assessment methodologiesHenk De Bleeeker

Bladzijde

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Geschiedenis en toekomst van het bekledingsprincipe 91Prof ir.Ton Venhoeven


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TU DelftDelft U n i v e r s ~ y ofTechnology

Symposium May 1(jh 2004

INTRODUCTION

Faculty of ArchitectureP.O. Box 5043NL-2600 GA DelftBuilding Technology: FaadesDr.lng.Just RenekensRoom 7.07T 31 152784094 or 31243244157E [email protected]

Active and interactive faade technology is nowadays common practice for mainly high performance officenew buildings and renovations. These modern faade concepts are improved during the nineties up tonow . The efficiency of these double layer faades including cavity ventilation and active sun blindsinstalled in the cavity is , however, under discussion. Too expensive, users unfriendly, too much unusablespace, increased cleaning costs, too high cavity temperatures amongst other points are opposed incomparison with modern single layer glass faades.Modern architecture, reliable weather independent solar control, low g-values, low U-values, improvedsound insulation, and for the second skin concept weather and building height independent naturalventilation are amongst others mentioned positive points.In this symposium speakers will present facts about the state-of-the-art of interactive and active faadeconcepts, and will introduce research results about sound insulation , wind pressure behaviour (pressureequalisation) , related standards throughout Europe, performance figures of interactive, active andtraditional faade systems, interactivity with HCVA-technology for inside climate control, prototypesimulation program mes and basics about faade architecture up to to-morrow's intelligent envelope.In this connection also facts about users' appreciation are presented , such as the conflict of interests dueto the use of cavity sun blinds for both energy efficiency targets as weil as individual comfort controlperformances.The importance of human satisfaction resulting in a high output (productivity) against energy efficiencysavings will be explained.One of the basic materials for high tech faades is modern glazing. Therefore a visit to the Glaverbel floatglass plant in Tiel is included (Mai 14th, 2004).The goal of this symposium is to forward knowledge about the state-of-the-art and recent research resultsin order to be able to answer the question for your projects: active and interactive glass faades - top orflop?

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INLEIDINGModerne kantoorgebouwen met omvangrijke glasgevels zijn boeiend en met de nieuwste technieken kanruimschoots voldaan worden aan de bouwregelgeving.Dubbelschalige glasgevels zijn actueel. In de verschillende uitvoeringen wordt een actief in de gevelgebracht waardoor de vertaalslag van buiten- naar binnen klimaat efficint kan geschieden. Hiervoorworden in hoofdzaak twee reguleringsvoorzieningen gebruikt: ventilatie van de gevelspouw; regelbare zonwerende installatie aangebracht in de gevelspouw.Bij een thermisch isolerende buitengevel en een op spouwafstand toegevoegd binnenblad, meestal eenenkelglasschiI , wordt een spouwbinnenzonwering geplaatst en wordt de spouw mechanisch metbinnenlucht geventileerd. In principe dienen in deze gevel geen te-openen-ramen opgenomen te worden .Deze uitvoering wordt klimaatgevel genoemd , of ook wel actieve gevel.Bij een uitvoering met thermisch isolerende binnengevel wordt op spouwafstand een extra buitenschilaangebracht , meestal een enkelglasconstructie, en in de spouw wordt een regelbare zonweringopgenomen. De spouw wordt natuurlijk geventileerd. Dikwijls zijn in de binnengevel te-openen-ramenopgenomen. Deze geveluitvoering wordt tweedehuidfaade, of ook wel interactieve gevel genoemd.Sinds de jaren negentig worden deze geveltypes met moderne middelen in talrijke varianten en spin-offuitvoeringen gerealiseerd. Daarbij is de interactie tussen dubbelschalige gevel en de klimaatregelendeinstallaties belangrijk. De goede bouwfysische waarden van deze geveluitvoeringen zijn mede te dankenaan de toepassing van (hoog rendement) HR ++ of (high performance) HP zonwerende beglazing.Er rijzen echter vragen over deze gevelconcepten in vergelijking met de enkelschalige glasgeveluitvoering: Zijn de duurdere dubbelschalige gevels in de operationele fase wel economischer dan moderneenkelschalige glasgevels? Hoe is de waardering van gebruikers van dubbelschalige gevels? Welke vooruitgang is geboekt na meer dan 10 jaar bouwen operationele ervaring? Zijn aannamesvan bijvoorbeeld hogere geluidwerendheid , windgedrag , g-IL TA-/U-waarden realistisch? Hoe bereiken we een verdere optimalisatie van deze geveltypes en hoe voorkomen we 'missers'?Moeten we eerst terug naar af en van daaruit stap voor stap eisen (regels, prestaties) , wensen(comfort , vormgeving , operationele efficintie) en mogelijkheden (technologie) vertalen naar de

optimale actieve/interactieve glasgeveluitvoering - intelligente bekleding?Welke onderzoek- en testmethoden zijn voorhanden en welke onderzoekresultaten zijn (binnenkort)beschikbaar?Een belangrijk punt bij de beoordeling van geveltypen, waarbij de zonwering een dubbele functie heeft -regulering van de energie-efficintie van de gevel , alsmede van de daglichttoetreding en het uitzicht - , isde strijd tussen centrale aansturing van de stand van de spouwzonwering voor energetisch zuinigebinnenklimaatregulering , interactief met de klimaatinstallaties, en de individuele aansturing ('overrulen')van de licht en zicht situatie op de werkplek. Een dilemma daarbij is dat de energiekosten nauwkeurigberekend kunnen worden , dus de energie-efficintie van gevel+installaties kan vastgesteld worden, dochhet voordeel van een hoger comfortniveau , dat zich vertaalt in een hogere productiviteit, lagerziekteverzuim, betere werksfeer, is moeilijk in geld uit te drukken.Dit is echter wel een bittere noodzaak, omdat de waarde van gebruikerstevredenheid een trede hoger ligtdan van bijvoorbeeld energie-efficintie.Tijdens het symposium wordt op bovenstaande aspecten ingegaan. En kunt u mogelijk voor uw projectenantwoord geven op de vraag: actieve en interactieve glasfaades - top of flop?Omdat het bouwmateriaal glas een belangrijk onderdeel is van dubbelschalige gevels hebben wijGlaverbel bereid gevonden u op 14 mei in de middag te ontvangen voor de bezichtiging van defloatglasfabriek te Tiel .Ik wens u een boeiende symposiumdag toe.Dr. Ing . Just Renckens,dagvoorzitter

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Double Ventilated Glass Faades - Acoustical performances

M. Blasco, Architect, EngineerConstruction Physics and Indoor Climate DeparfmentBelgian Building Research Institute

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IntroductionModem architecture and Double Ventilated (Glass) Faades (DVF) are often related to oneanother. Many European cities increasingly want to profile themselves as belonging to thearchitectural elite. When one looks at the complexity of the subject, it is not surprising thatonly larger architectural offices are able to undertake these more ambitious projects. Itrequires a multidisciplinary approach with a team of specialists in several areas: ventilation,acoustics , stability, fire, hygrothermics, daylight,...Various aspects of acoustical faade insulation are dealt within this document. Oneproceeds on the assumption that the reader is familiar with basic acoustics and with thetypology of DVF (see the BBRI website: www.bbri.be/activefaades) .There are reasons why the use of DVF can be favourable: increased acoustical faadeinsulation, transparency of the faade, use of solar protections up to great heights,possibility of opening windows at great heights, architectural image and statement,favourable energy performances, improvement of hygrothermal comfort, better use ofdaylight,...Negative aspects are sometimes mentioned, such as maintenance, investment costs,.. .

Parameters ofperformancesWhen determining (simulation) the acoustical performance of a DVF , one starts from theacoustical performances of the various (constituent) elements measured in the laboratory.By combining these data and applying one or several prediction modeis, one can (byapproximation) do a correct acoustical performance determination. Usually one is interestedin knowing what impact changing one of the elements of a faade has on the overallacoustical performances (e.g. changing the outer faade from type A glazing to type B).Mathematical models can provide an answer to this, but (still) only by approximation , sincethey are prepared for infinite walls and generally do not contain an entirely correctformulation of the various junction points (ref. the new European standard EN 12354) andedge effects. A great deal of research can still be performed here. The question ariseswh ether, with pragmatic resources , one cannot arrive at a range of solutions : this means, onthe basis of fundamental acoustical principles and their impact on the overall performances,making a forecast which yields no precise values, but rather a series of results fluctuatingbetween a minimum and maximum value. This could be called a type of preliminarycalculation .

Var iatien due to : changes inmo rphelegy I mounting I sub-types

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Type DVF


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The acoustical performances will depend on the materials used in the structure andon the configuration (geometrical arrangement) of these parts. The materials used for DVF will primarily be: glass, steel and concrete. The configuration used is nothing but the constructed typology (width of cavity,ventilation inner-inner,...).

If one wishes to calculate a faade insulation , one bases oneself on measurementsperformed in the laboratory on the glazings and wall parts. Vet the insulation of theseglazings is measured in the laboratory for specific (standard) dimensions according to thestandard EN ISO 140-3 (1995). These dimensions are: 1.23 m x 1.48 m. This is small if onecompares this with the dimensions used in the practical cases. The fact of using largerdimensions in practice already entails a reduction of the acoustical performances.Other parameters - such as air impermeability of the faade , absorption cavity, flanking , userconditions of the inner faade , and so on - will also determine the ultimate performances onsite.

Under the acoustical performances of a DVF can be understood: the faade insulation the acoustical insulation between rooms located on the active faade side("flanking" or lateral transmission via the cavitvJ

Standardisat ion :; .........,. Faade insulation tEN 12354-3: 20001

Depends of !he elements of !he faade

.. ... " ' ~ Flanking (EN 12354-1 2000 1Depends primarily of Ihe separating element

' ~ - : ; ~ ,,," :::1JThrough walls, ceiling , floor Faade I junction I? i

Acoustical measurements

tmeasurement: EN 10848-1 :20001

Through Cavity (Annex F) ::hJThrough holes (conducts)

Overview ofsame results ofmeasurement campaigns for faade insulationofDVFBelow we find several acoustical results from a number of measurement campaignsperformed by the BBRI within the framework of the Active Faades project (financed by theMinistry of Economic Affairs in Belgium). The most important typologies of active faadeswere measured in the areas of acoustics, ventilation , hygrothermics and daylighting.The acoustical (faade) insulation spectra are presented as weil as the single-numberratings. The measuring method is in accordance with EN ISO 140-5 (1998), the singlenumber rating was calculated in accordance with EN ISO 717-1 (1996).

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For volumes smaller than approximately 100 m3 it is recommended (see NBN 801-400) touse the "normalised gross acoustical insulation" D 1s ,2m ,n. For bigger volumes we use the"standardised gross acoustical insulation" Dls,2m ,nT. These two parameters are spectralvalues.The single-number ratings are marked with a sub-index "w" and are calculated from thesespectra I values, for instance D 1s ,2m,n,w and D 1s,2m ,nT,w.These values come with two correction terms C and Ctr for mid-high frequency soundsAnd low frequency sounds respectively. As an example we have: Dls ,2m ,n,w (C ; Ctr) = 43 (-2;-5) dB . We yield that this faade has an insulation of 43-5 = 38 dB against low frequencysounds and for mid-high frequencies it has an insulation of 43-2 = 41 dB.

Measurement campaign 1 (climate faade):The faade element of the measured room includes two modules (2 x 1.5 m width)composed of a glass outer and inner faade. The glass inner faade is hinged and can beopened. In the closed state the inner faade has at the botlom a ventilation slit of 1.5 cm inheight over the entire width of the module (the air in the room is extracted via the slit into thecavity and upwards via the false ceiling) . The inner faade is only opened for maintenancereasons.

Measurement acoustical faade insulation climate faadeInterior view office Typology climate faade

volume of room : 50 m'D1s,2m ,n,w (C;Ctr) =38 (-2;-5)dB (inner faade open)D1s,2m ,n,w (C;Ctr) =43 (-2;-5) dB (inner faade closed)

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inner faade: single glazing 6 mmouter faade : double glazing 6-12-8cavity depth: 12.5 cm


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605040

c_ 30EN:ti 20c 100 00

Faade insulation small bureau

o 0 0 0 0 0 0 0


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Faade insulation small bureau

60_ 50m:E. 40ce- 30 - l I - " i - - ' r - - - - - ' L -

interior panescompletely open___ interior panes

closedC;; 20o 10O +o---.-"---'-'---'--"---'-'---'--,,-'--.---r-lo 0 000 000000


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Faade insulationro ,---------------------------------

r _ - - - - - - - - - - - - - - - - - - - - - - - - - - ~ ~r _ - - - - - - - - - - - - _ ? ~ - - - - - - - - -iii , /0-

:!!. 40 r _ - - - - - - - " -' ------------------------ , - - - - - - - - - - - - - - - - - 1.Y 1__ outside -> 1st 1I00rMeeting Room :i . / ~ ( - 1 - 5 ) d B

Cr _ - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

10 r---------------------------------

100 1ro 250 400 630 1k 1.61< 251< 4k

Freq . (Hz)

Comparison with traditional faadesIn Belgium the average faade insulation for residential construction lies at about 35 dB(A),taking into account the share of glazing , ventilation grid, roof, etc.In office buildings, the requirements for faade insulations (according to NBN 801-400:1977)are identical to those for residences, taking the underlying functions into consideration. Therequirements vary from 26 dB(A) to 41 dB(A), depending on the prevailing noise leveloutside. It is clear that with the use of active faades one obtains performances which meetthe highest requirements of the Belgian standard. It is also evident that the "non-DVF"demand a thorough acoustical study and effort in order to obtain performances equivalent tothose of the DVF.The acoustical faade insulation of DVF (based on the measurement campaigns) lies above43 dB . This corresponds to the acoustical performances of 14 cm of brick (180 kg/m 2 ) . Theacoustical performance of the double faade (as in measurement campaign 3) of 54 dBcorresponds to the acoustical insulation of 14 cm of poured concrete (350 kg/m 2 ) or 19 cm ofconcrete blocks (285 kglm 2 ) .A typical faade from an office building gives 6 dB less acoustical faade insulation than thepoorest performing DVF.There are quite a few parameters which influence the acoustical performances of a DVF .These are: type of faade system I type of glass I size of glazed surfaces I properties ofreceiving room I openings I cavity depth I resonance of one and two layers I sourcepropertiesMost of these parameters are also applicable to traditional faades .

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Flanking sound or lateral transmissionThis concept is important when considering the acoustical insulation between the roomslocated on the faade side. It includes the sound which goes from one room to the other viathe cavity of the DVF , especially when the (glass) inner faade can be opened. The impactof this on the acoustical insulation between the rooms is less important between two roomson the same story than between two rooms situated above one another. This is because inmost cases with these buildings (generally office buildings) the vertical partition walls aremade of light materiais, while the floors are made of (heavy) concrete. The light verticalpartition walls provide less acoustic insulation, and thus the sound that comes in via thecavity (from the adjoining room) will be less noticeable.Such acoustical insulations are computed by using formulas which are based on theformulas for lateral insulation (analogue for suspended ceilings) for airborne soundtransmission via the cavity. Specific formulas for this have been established in the Europeanstandard EN 12354-1 (appendix F) (2000):

Ao = 10m 2 (reference)C : depends on the position of the opening relative to one another. If the openings are at a90 angle to one another and less than 1 mapart, then this term amounts to -2 dB. If theopenings are coplanar or further than 1m from one another, then this term amounts to 0 dB .In determining Rhr or Rhs lab data are taken, and the composite insulation has to be takeninto account if there are several (different) materials or openings .

:CHOIV"OIJ ( U C m ~ , ~ . (11\'11)''\ 11

Overview of the flanking (lateral) transmission results

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Measurement campaign F1:For this measurement the lateral insulation was measured, thus including the impact of thecavity for a double faade. Given the volumes of the offices 100 m') we opted todetermine On rather than OnT.

Measurement acoustical flanking transmission through the cavity for adouble faadeLongitudinal section building

D1. Dn,.,w(C;Ctr) =56 (-1 ;-5) dB2. Dn..w (C;Ctr) =35 (-1;-5) dB3. Dn..w (C;Ctr) =50 (-1 ;-3) dB /3 7 (0;-1) dB4. Dn ..w(C;Ctr) = 49 (-1 ;-3) dB

Intenor view cavity

Typology Double Faade

inner faade: single glazing 8 mmouter faade: double glazing 10-12-8cavity depth: 90 cm

Intenor view office

The background noise was also measured in the respective offices (= 28 dB(A)). In thecavity of the double faade the background noise amounted to 44 dB(A) . At street leveloutside the building the background noise amounts to values between 65 dB(A) and 70dB(A).

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The most important flanking path between 2 stories is along this cavity. All measurementswhere undertaken with all windows closed, th at is including the windows from the innerfaade, except where mentioned.Discussion measurement 1:This measurement always yields the best results. The direct transmission surface is also thesmallest. Flanking via the vertical walls is very limited since they are disconnected in thevertical direction, in other words there is no vertical continuity, except by the cavity, thoughhere the path through the cavity is longer than for measurements 3 or 4.

Discussion measurement 2:For th is configuration, i.e. between offices in the horizontal direction, the impact of the cavityis limited. This is because the vertical walls are light (system) walls. Thus intrinsically theyhave an airborne sound insulation which is fairly limited. One must also examine whether ornot there is a suspended ceiling which conneets the two rooms; this can also influence theacoustic insulation . Here this was not the case.

Discussion measurements 3 and 4:The results are symmetrical for both from above to below and vice versa. We expect alimitation of the airborne sound insulation due to acoustical insulation losses through thecavity.For the measurement from above to below (measurement 3) one calculated the impact ofthe opening of a window: the opening of a single window in a single office leads to areduction of 13 dB for the airborne sound insulation. One can ex peet that the result achievedthen corresponds to the airborne sound insulation of one single glazing (8 mm), equal toaround 32 dB , increased by the screen effect of the cavity, which approximately comesdown to an airborne sound insulation of 37 to 40 dB (note: the standard EN 12354-1appendix F takes this into account with the introduction of the C coefficient).

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Overview of measurements as a function of the geometricalcharacteristics of the DVFCF : Climate Faade (Active faade)OF : Double Faade (Passive faade)OW: Double WindowlAF: Inter active faade

Type Cavity Interior pane Exterior paneAF [cm] [mm] [mm]

CF 12 .5 6 6-12-8

OF 70 6-12-8 6-12-8OF 1 70 6-12-8 6-12-8DF 130 6-12-8 6DW 7 10 6-12-8

lAF 12 6-12-8 6lAF 12 6-12-8 6

Design guidelines DVFFormulation of the problem

Volume Ols,2m,n,w Remarkrecep. Room (C;Ctr) [dB][m']50 43 (-2;-5) Open int.

38 (-2;-5) pane24 53 (-1 ;-2)

5000 54 (-1 ;-1)93 .1 50 (-1 ;-5)47 47 (-2 ;-5) Open int.

41 (-3;-5) pa ne35 46 (-1 ;-6)

> 500 52 (-2;-7) Openspaceoffices

VVhat requirements are imposed on the DVF ? One can answer this by looking at the variousrequirements separately (acoustics, ventilation , ... ) (serial) or by applying a multidisciplinaryapproach (parallel).It is clear that the various disciplines have an impact on one another and th at one will haveto seek a sort of "greatest common denominator". Ultimately, the economie factor willgenerally play the decisive role.The serial approach (look at disciplines one after another) has the advantage of offering astructured way of working. The disadvantage is that the sequence (order of disciplines) canplay a major role. One solution would be to implement several different sequences andcheck whether one obtains the same decisions.

1 Measurement based on the reverberation correction term18


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Design tools acoustics DVFFor the preliminary design of a DVF, one possesses a number of ''tools'' for arriving at anacoustical optimisation in the area of faade insulation and longitudinal insulation:

standards calculation methods

a. Faade insulation:The acoustic "Eurocode" for this is the EN 12354-3 (2000). This proceeds fromlaboratory measurements of the various components in order to determine the faadeinsulation on-site, taking into account the 3-dimensional character of the faade(projecting parts,...) and any openings in the faade (composite insulation). Theproblem with this standard is th at double-wa lied systems are not yet implemented; thismeans that it cannot take account of the specific properties of a double-walled system(MSM or 3 chamber model). This will be the subject of research in the near future.Yet one should be ab Ie to use the standard by regarding the 2 cavity wall skins asindependent and applying the standard separately for each cavity wall skin. This impliesthat one assumes the 3 chamber model (superposition principle) . This will be correct asof the frequency where the 3 chamber model applies.b. Lateral transmission:The European standard EN 12354-1 (annex F) (2000) offers a solution . Generally th isrequirement will not be a limiting factor for the choice of the inner glazing, the faadeinsulation will be a stricter requirement. However, the positioning of the possibleopenings in the inner faade is important. The lateral transmission vertically (betweenrooms on different stories) will be more important than horizontally (between roomslocated on the same story) since the floors display a greater acoustical insulation thanthe (lighter, movable) partition walls.

Application of normalisation to the prediction of the acoustical faadeinsulation and lateral transmission for the implemented measurementcampaignsThe following summarises a number of ideas for applying the model described in EN 12354-3 (2000) and EN 12354-1 annex F. This prediction is compared with the on-sitemeasurements.Determination in accordance with EN 12354-3 (2000) for the faade insulation

1. Single-number method:Conclusion:Using the Mass-Spring-Mass model and the 3 Chamber model and direct field conditions wehave: A single-number rating is largely determined by the performances in the lowfrequencies. We thus see th at the application of this method with single-number ratings isnot precise: this method yields a major overestimation or underestimation of theperformances (measured on-site: 45 dB). A spectral approach can yield a more preciseresult (based on one third octave bands) .

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2. Spectral method

Conclusion:Using the Mass-Spring-Mass model and the 3 Chamber model and direct field conditions wehave: On-site we had measured 45 dB (for Dls,2m,nT,w) . The prediction with the aid of thespectral values (44 dB) in first instance gives a good and much better approximation thanwith the single-number ratings alone, because we can make a distinction between thedifferent ways of sound transmission (MSM or 3 chamber transmission). The spectralapproach requires more calculation than the single number approach.

Determination in accordance with EN 12354-1 appendix F 'or lateral soundtransmission (in closed state)Spectral method (Iongitudinal sound transmission):Conclusions:

The prediction with the spectra I method gives as single-number rating: Dn ,s,w = 52dB. On-site we measured Dn,s ,w = 50 dB . Assembly errors and air leaks can furtherreduce the performances on-site compared with forecast calculations. This meansthat one must take this into account when making predictions. In this case, theprediction corresponds weil with the measured value if we subtract 2 dB for airleaks and assembly errors.

One must take into account a reduction of the performances because of the largersurface areas of the glass (than in the laboratory). This can lead to reductions of 3dB , and is particularly important when the surface exceeds 10m 2 . Air leaksbetween inside and outside additionally lower the insulation (up to 2 dB).

The screening effect of the elements th at can be opened in the inner faade will play a rolein the overall acoustical insulation: th us, two openings which "look" at one another will beless favourable.

more negative fo r Dn,s more positive fo r Dn,s

The sound reduction indices Rh are determined proceeding from the sound reductionindices of the elements from which the wall is composed (composite insulation) . The sealantjoints are also taken into account with the aid of a sound reduction index. In the case ofdouble faades where longitudinal transmission applies, the cavity (between the inner andouter faade) will spread out over a large number of rooms . In other words, the cavity is notlimited to 2 rooms positioned next to one another or above one another. In order to takeaccount of this when determining the longitudinal transmission between 2 rooms, one willhave to take into account an additional fictive equivalent absorption surface area.

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Literature list "La faade double peau" - EPFL Architecture Department 1998 - Prof. A.P. Faist {( Double Skin Faades - Oesterle. Lieb.Lutz.Heusler. 2001 {( Jaarrapport Actieve Gevels - MEZ - BBRI Construction Physics Department

2001 "Hogere cursus akoestiek-Bouwakoestiek" - KUL. Applied Sciences Department2000. Prof. GVermeir "De tweedehuid faade" - Adviesbureau Renckens 2000. J. Renckens "Performances acoustiques des faades et des couvertures" - CATED June 1993- M. Mayerowitz (CEBTP)

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Symbiosis of Faade and Climate Installations

A.H.C. van Paassen,W.J. SteeTU Delft, Mechanical Engineering, Mekelweg 2, 2628 CD, Delft, the NetherlandsEmail : [email protected]://www.ocp.tudelft.nl/etiResearch/EnergylnBuiltEnvironmentiSecondSkinFacadeIDSF/index.htm

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AbstractOne of the main arguments supporting the application of multiple facades is the reduction inenergy consumption and capacity of the HVAC system . However the impact of thesefacades strongly depends on the overall design of several components of the building likefaade, climate installations and control system. This paper presents several tests of thebuilding with different selection of the components. The tests are carried out with thesimulation program built in Simulinktm. To validate the model measurements were taken inthe test cell at TU Delft as weil as in a real office building. Each test is qualified based ondifferences in capacities , energy consumptions and costs for various solutions of faade,climate system and control.Based on the simulation result a cost effective integrated concept, called "DeltaClimat", isintroduced.Keywords: Natural ventilation, Double skin faade, Control, Simulation

IntroductionThe demand to reduce the energy consumption of the indoor climate installation (HVAC) ispushing designers into application of new solutions. There are several ideas that are gainingattention due to their saving energy abilities. Among them there can be distinguished:multiple skin faades, natural ventilation, and night cool ing.Previous research (Saelens 2002) analysed impact of different faades on the energyconsumption of the building. The best appeared to be traditional faade with the externalshading. Compared systems however, were not optimised conceming the integration ofdouble skin faade (DSF) and HVAC by control system.Innovative designs require flexibility in simulation. It is important to have a free access to thesimulated phenomena and create one's own components or easily optimise the existingones. That is why the simulation code Matlab/Simulink was used. Additional advantage ofSimulink is that it is a sort of platform in which many people from different research groupsmay produce their own components that can be exchanged and used by other groupswithout any adjustments. There are already several platforms existing in which differentusers of Simulink may exchange their models (Riederer 2003; Weitzmann et al. 2003).A dynamic simulation model of the building together with different faade constructions asweil as HVAC system and integrated control strategies was created. With the use of thesimulation model various possible settings of the building could be qualified conceming theenergy consumption, capacity of the system and indoor comfort quality.Simulation modelThe simulation model of the building with the additional components such as double skinfaade, HVAC system and control strategies was implemented in Simulink. The pre-processing of input weather and building data was done with Matiab. Matlab functionextracts from the general weather matrices values of the temperature, solar radiation or windconditions. Based on this information it calculates the weather inputs referenced to theparticular building, like distribution of the wind pressure (Grosso 1992) and solar radiationon each surface of the building. The connection between Matiab and Simulink is shown onthe figure 1.The library of possible components is built in Simulink. Apart from the main body of thebuilding, there are several options for the faade, HVAC system and control strategy. Table1 shows the exemplary selection for each of the group. Every simulation model with differentcomponents was validated with the use of measurements and other simulation programs.

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Matlab---

Simulink Matlabpreprocessor .. programm postprocessor

Figure 1. Scheme of the data flow in the simulation model.

Table 1. Exemplary selection of components of the building inside of Simulink.Facade HVAC system Control strategy

Passive and active Double duct ventilation components (hybrid Single duct ventilation ventilation)

] -Lr Natural ventilation Night coolingj Complete air handling unit Weather prediction Others ... Day light control Others...Others ...Basically, the library of facades was used to analyse thermal and airflow performance of theexternal faade. This means that temperature and airflow distribution in the faade wasverified for different selections of construction, functions and materiais. Afterwards thefaade was combined with the other components of the building to determine the totalperformance of the building. To draw reliable results the simulation needed to be done forthe period of a whole year. The possible results were;1. Yearly energy consumption for heating, cooling and ventilating ,

2. Indoor comfort quality,3. Necessary capacities of the system,4. Monitoring of all possible variables like temperature and airflow distribution in eachpart of the total system.The main window in the library is visualised as shown in figure 2. By entering each of thegroups it is possible to make aselection for each component of the building and to copy andpaste it to a new window. After connecting the data input from the workspace of Matlab withthe desired parameter values the simulation can be realised. Exemplary settings of thesystem are shown in figure 3.

F" Ed it: ... . . . ShuIIotIon Fan " Tao" HIi9[) I al f li l , .. 4 5 mi .. IH__ : i jo ~ - ~ I Jt l lI I I ! r i ll J . l ~ ROOM MODELS HVAC + CONTROL FACADE

Figure 2. Library ofthe components in Simulink.26

, . . . . . .'-'"

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r OsunI IT,Osun ,windVel,Toutsldel T glass r Tglass-. VV1 ndVelocity Twallmean r - rt' Twall meanToulsideFrom Workspace Twall meana sun inside Osun inside

Troom . . Tc8'lity . . Tradiator.. DSF positions Tc8'lity Tradiator Troom TroomDSF + BLiNDS ... Toutside aHVAC .. aHVAC

. . Troom positions_DSFl ROOM PMVHVAC +Control

Figure 3. Example offhe simulafion program creafed in Simulink.

A great number of possible simulation settings needed to be validated. In general there werefour tools used to validate different options of the building:Laboratory test facility at TU Delft,Test cell at TU Delft,Real office building with double skin facade (Unica in Zwolle),Standard design programs (VA BI software).

The laboratory test facility (fig. 4a) allowed for the measurements in fully controlledconditions. Measurements under real weather conditions were done with the test cell at TUDelft (fig. 4b) and in the office building in Zwolle (fig, 4c), which both have the same doublefacade. The test cell allowed for running the measurements for different settings of thefaade and intemal system . Several sorts of glass could be applied as weil as different sizeof the ventilation openings, positions of the valves in the cavity, blinds and windows, Thisvariety of available settings made verification of the model of the building with the doubleskin faade very universa!. More detailed description of the validations is given in (Stee andPaassen 2002b).Figure 5 shows the exemplary comparison of measured temperature with the simulated one.The comparison is done for temperature of the air in the middle height of the faadebetween the blinds and the window.Although the difference between the measurements and simulations may achieve even 5Kthe observed sensitivity of the real facility and the model proved to be very similar,Additionally, another validation of the model was conducted with the standard designsoftware (VABI) by comparing outputs for the traditional building.

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Figure 4a .Laboratory test facility atTU Delft

45

40

Ol:; 35Ol0 ..E

30

0.2

:/Figure 4b.Test cell at TU Delft

Temperalure in Ihe cavily

0.4 0.6 0.8 1.2

Figure 4c.UNICA office building in Zwolle,NL

1.4 1.6 1.8 2Day number (17-18 .08 .02)

Figure 5. Comparison ofthe temperature in the cavity (measured in Test cell and simulated).

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Integrated control strategyOne of the major problems related to the effective application of the double skin faade inthe building is integration with the installations. The main difficulty is encountered inconnecting the functions of the HVAC system with the faade. So far application of thedouble skin is usually limited to the individual control of the faade apart from theinstallations while integrated automated control with manual overriding will allow the doubleskin faade to increase energy savings.

Table 2. Application possibilities for each device of the DSF.Device Function Effect Period Priority LimitationsFresh air High Occupied Isupply Noise of the windows'Window Room actuatorstemperature High All 11

Cavity Small All 11 Efficiency depends on the airValves temeerature tightness of the valvesWind pressure High All IdampingDaylight High Occupied I Adjustments may be disturbingBlinds for inhabitantsRoom High Unoccupied 11temperature

As a principle the control strategy give priority to the use of the passive components of thebuilding like windows, blinds, valves in the cavity of the faade. The more these componentsare used the higher energy savings. Whenever it is possible, the natural ventilation isenabled. The simulation showed that for the Dutch climate natural ventilation can be usedfor 35 up to 40% of the occupation time during the year . This may already bring highreductions in the energy consumption. Furthermore, the passive components can be used tosupport the HVAC system.Each of the components of the faade has different function and influence on the indoorcomfort. In general, the possible functions of the DSF in the HVAC system are grouped inthe table 2. It shows also the effect of each device on the function as weil as applicationperiod, priorities between the functions and possible limitations. Control of each componentshould be described very carefully and all the aspects should be taken into account. In caseof the overlapping of two functions for the same component the priorities need to be set.Selection of the priorities depends on the influence of the component on the comfort andpossible support of other components. For example, blinds control the daylight in the room.This needs to be first priority because blinds are crucial for daylight. Overriding the daylightfunction of the blinds by the function of controlling the temperature is bringing directlyexceeding in indoor comfort (glare) or is leading to the not reasonable increase of theenergy consumption (artificial lighting). However, for the unoccupied period the light level isnot important. 81inds will be then controlled by the temperature function.Valves in the cavity are important to damp a wind pressure. They can protect the interior ofthe building from draught. Position of valves can be set simultaneously because there arenot any limitations such as noise and visual disturbance. On the other hand, effect of thevalves on the temperature in the cavity is relatively small. Additionally, it depends stronglyon the air tightness of the valves. Even very small leakage will cause high reduction intemperature control abilities of the valves.Windows supply fresh air and influence the indoor temperature . However, a designer of thecontrol strategy for the window of a single faade should be aware of the outside air quality ,noise caused by the actuator and transmitted from the outside, draught , rain and burglaryproblems. Since 50 many considerations need to be taken into account, the usage of thewindows may be limited or even disqualified.

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The double skin faade improves the usability of the windows because it protects thewindow from sudden wind pressure changes, rain and burglary. It also improves the noiseattenuation and it may have some abilities to filter and cool the air by using plants, forinstanee. (Stee et al. 2004)The remaining problem is the disturbing effect of the window's actuator. The windowpositions cannot continuously be adjusted by feedback control of the room thermostat. Itwould divert the attention of the inhabitants from their work. Instead a rule based feedforward control is applied.The advantage of the natural ventilation is the possibility of using it during unoccupied periodwithout wasting energy. Higher ventilation rates may cool down the building more effectivelyduring the night. Night cooling used by the building brings enormous reductions in energyconsumption and capacity of the HVAC system (paassen et al. 1998). This item helps tojustify the application of double facades a lot.

Table 3. Basic data of the selected room .Dimensions of the room 3.6 x 5.5 x 2.8 mFalse ceiling YES (apart from the system no 9)Orientation of the facade SouthFacade Fully glazed, Systems 1-8 have a high performance glass HR ++.System 9 that has a clean glass.Mass 75 kg/m" (Medium) of the accumulation areaIntemal loads 25 WIm" of the floor areaVentilation flow 2 ACH for mechanical ventilation .For the natural ventilation 3-11 ACH depending on the windspeed and direction .Night cooling Default temperature set point 21 C. With the predictive control21-18COffice hours 8 - 18 o'dockSide walls plaster panels

Energy testsThe validated simulation model can be used to run simulations of the building with differentdesign and settings of the HVAC system or with different construction of the faade. Herethe comparison of the energy consumption and capacities of the HVAC system is presentedfor selected designs of the faade and the HVAC system. Alt kinds of innovations are usedsuch as night cooling by mechanicalor natura I ventilation, predictive control, curtain walt anddouble skin facade. The results should qualify each of the selected technologies .All the systems are compared concerning:

Energy consumption by the HVAC system (ventilation , cooling, heating), Capacities of the cooling and heating system to fulfil the required indoor comfortconditions. Acceptable exceeding of indoor temperature above 25.5C should notexceed 100 hours of the office time per year.The room selected for the analyses is surrounded by similar rooms from each side, so apartfrom the faade none of the walts is external. The data of the room is shown in table 3.Table 4 shows the selection of the solutions chosen for this study. This selection was builtconcerning the glass faade, the mechanical ventilation system and natural solutionssupporting the mechanica I ventilation.

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The first eight systems represent gradual changes in the external faade and others savingenergy applications. The last solution is a trial to reduce significantly the costs of theinstallation.Table 5 shows the capacities required byeach system as weil as the energy consumption .The capacities of the cooling and the heating systems were established by iteration in orderto fulfil the condition concerning the indoor comfort .

Table 4. Data of the selected systems.No Glass Faade Mechanical system Natural system No.j HR++1 UWindow=1.2W/m2K, 1ZTAtotal=0.26 ,ZTA=G-value NO2 2I - -

HR++3 UWindow=1 .2W/m2K, Mechanical night cooling 3

ZTAtotal=0.14,t--- Natural ventilation through4 operabie windows + Night 4Balanced +Heat cooling + Predictive controlRecovery (80%) +

-'7 Individual/ ' coolinglheating/ ' HR++/ '/ '

W/m2K,5/ ' Uwindow = 1.2 5/ '/ ' ZTAtotal=0.20- Mechanical night cooling

6 6I--

HR++, Natural ventilation through7 Uwindow= 1.2 W/m2K, opera bie windows 7ZTAtotal=0.095 + Night coolingI--- 1/8 Natural ventilation through 8I-- operabie windows

UwindoW= 1.6 W/m2K, Supply duet + Top + Night cooling9 cooling + Individual + Predictive control 9ZTA total=O .12 heating

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Table 5. Energy perfonnance of the southem faade per m2 net floor area.Capacity [W/m2] Energy [KWh/m2) Total

Facade Cooling Heating Cooling Heating Transport CostNo . Thermal Thermal Electric [Im2) [%]1 19,00 50 74,10 4,75 2,94 4,01 100,002 13,00 50 54,30 8,40 2,94 3,20 79,703 8,00 50 29 ,85 8,05 3,44 2,12 52,744 5,00 50 10,55 7,95 1,76 0,98 24,375 12,00 50 48,6 5,9 3,44 2,93 72,946 8,00 50 30,5 7,25 3,44 2,12 52,907 6,00 50 12,60 7,35 1,76 1,06 26,318 4,00 50 8,55 7,10 2,09 0,90 22,539 6,00 90 10,5 15,50 1,46 1,16 28,90

Energy consumption tor each system90,0080,0070,00 60,00_ 50,00j 40,0030,0020,0010,000,00

System 2 3 4 5 6 7 8 9I cooling heating 0 transport I

Figure 8. Primary energy consumption for each system in kWh/m2.

From the energetic point of view the worst is installation of the blinds inside of the room.Placing the blinds outside the window may bring reduction in the cooling system capacityand its energy consumption by about 30%. In general, the faade with the external blindsand the double skin faade perform the best. Logically the perfonnance of the building withthe external blinds (cases 2,3,4) should be better then for the double skin faade (cases6,7,8) . However, the following example shows that it is not a rule. The advantage of thedouble skin faade is its flexibility concerning the design. For th is study a deep cavity ot0,6m was selected with big openings on the bottom and the top of the cavity. The deepcavity created an overhang that significantly reduces the direct solar radiation falling on thesurface of the window. Additionally, blinds were placed next to the external glass of thefaade. All these caused the concentration of the hot air at the side of the external glass,which is away trom the window. As aresuit the solar protection factor (G-value or ZTA)could drop below 10% (tabie 3).

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The curtain wall (system 5; in Dutch it is called " klimaatgevel") improves the performance ofthe building in comparison with the faade with the intemal blinds . The energy consumptionas weil as capacities of the HVAC system and G-value are lower then for the single skinfaade with the intemal blinds. Nevertheless, it requires cooling units with 30% highercapacity and proportionally it consumes more energy for cooling then comparable solutionswith extemal blinds (system 3) or double skin faade (system 6) . Additionally construction ofthe curtain wall does not allow for the natural ventilation through the windows openings .Other significant issues, which importance was determined here, are the application of nightcooling and natural ventilation. Applying night cooling by mechanical ventilation only may cutthe cooling capacity and the energy consumption by factor of 40% without any extrainvestment. This can be seen by comparison of case 3 and 2. The use of the naturalventilation together with the night cooling brings further crucial reductions. It may save 60%of the cooling capacity and 70% of the energy consumption used for cooling (comparison ofthe case 4 with 2).Furthermore, the predictive control can make the night cooling even more effective. This isshown by comparison of the system 8 with 7. Application of the double skin faade (orcomparable extemal blinds) together with the natural ventilation and night cooling withpredictive control may cut 78% of the initial capacity of the cooling system. The energyconsumption for the cooling can then be reduced by 90%. We can conclude that mechanicalcooling can be omitted if we accept some more hours with higher temperatures . It isemphasised that this counts only for intemal loads not exceeding 25 W/m 2 .

Table 5. Annual costs spent for the DSF, HVAC and energy.Costs for each system [Euro I m2 annually]System 1 2 3 4 5 6 7 8 9

Facade 18.69 19.35 19.35 20.15 26.84 30.91 32.37 32.37 28.29HVAC 17.68 16.88 16.08 15.28 16.88 16.08 15.6 14.8 7.44Energy 4 .01 3.2 2.12 0.98 2.93 2.12 1.06 0.9 1.16Total 40 .38 39.43 37.55 36.41 46.65 49.11 49 .03 48.07 36.89

CostsThe price plays the crucial role in selection of the faade. Since the faade is the mostimportant component of the HVAC system, the final comparison should be based on thetotal price of the DSF and HVAC system. It was noticed that the cases 1 to 8 have graduallymore expensive faades and higher reductions in energy consumption. Therefore, thesystems with the double skin faade (6 - 8) are in the final calculation (tabie 5) the mostexpensive although a reduced cooling capacity leads to cheaper installations. Optimisationof the HVAC system was done only for case 9. Here, the double skin faade played the roleof the ventilation duct in the building. Price of the installation was cut almost twice withcomparison to the other cases. Furthermore, the case 9 is still one of the options with theleast energy consumption. This makes it one of the most economic solutions among allconsidered ones.The remaining question is ; why not to optimise the design of the HVAC system for thebuilding with the extemal shading only . Certainly, it would limit higher costs of the faadeand most probable maintain very high energy reductions. On the other hand, application ofthe single skin faade puts again some limitation on the free windows openings mentionedabove. The usability of the windows openings can be decreased then drastically. The sameaccounts for the outside shading. They can not be applied in high rise buildings.without theprotection of the double faade.

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Finally, the choice for the single skin with the outside shading or double skin faadedepends not only on the ability of controlling the thermal behaviour of the building but alsothe other aspects like aesthetics, noise attenuation, transparency, etc.Based on these simulation results a cost effective concept "DeltaClimate" recently wasintroduced by Rollecate (faade) and Unica (instalIer) . It is more or less similar with case 9.More details can be found in the appendix.

ConclusionsThe article shows the importance of an integrated design of the building installation togetherwith the faade. Since the faade plays a role in creating the indoor comfort it can beconsidered as a component of the HVAC system. That is why the design of both HVACsystem and faade should be optimised to reduce the costs and the energy consumption.In order to allow for optimising the total building design the simulation model was developedand validated successfully.Furthermore, the simulation program was used for qualifying different ideas in the buildingdesign including HVAC and the faade. Several possibilities for the design of the facadesand the HVAC system are compared by year round simulation of the performance.From the thermal and economic point of view the building with the double skin faade maysuccessfully compete with the traditional building with external shading. The choice of thebuilding depends not only on the construction of the double skin faade but also on thesimplicity of the HVAC system. In th at way the higher costs of the faade can becompensated.It seems that the curtain wall does not bring many advantages apart from the fact oflowering the G-value (ZTA) and improving the heat recovery in the cold season. Moreover,a big disadvantage of the curtain wall is that it does not allow for the natural ventilationthrough the operabie windows.Natural ventilation is a crucial component for reduction of the cooling system. Even simplenight cooling by mechanical ventilation may save around 40% of the cooling capacity andenergy. Application of the natural ventilation by automatic operabie windows and simplealgorithms for predictive control allows for further reductions that can reach in total even70%.Costs of the double skin faade should be calculated together with the total costs of thebuilding. Since the more functions the faade is taking over of the building installations thehigher the initial costs of the faade can be accepted. The example given in this paper (case9) proofs that costs of the faade may be compensated by the smaller HVAC installationwhat together with the low energy consumption makes this case the most economic solution.

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AcknowledgementThe authors like to express their appreciation for the contribution from B. Grninger (Unica)and A Smit (Rollecate). The research work has been supported financially by Novem.

ReferenceGrosso, M. (1992). Wind pressure distribution around buildings: A Parametrical Model.Energy and Buildings, vol. 18, pp 101-131 .Paassen, AH.C . van, Liem, S.H. and Grninger, B. (1998). Control of nightcooling withnatural ventilation. 19 th Annual AIVC Conference, Oslo, Norway.Riederer, P. (2003). From sizing and hydraulic balancing to control using the Simbad tooibox.Eight InternationallBPSA Conference, Eindhoven, Netherlands.Saelens, D. (2002) Energy performance assesment of single storey Multiple-skin facades.

Katholieke Universiteit Leuven, Leuven.Stee, W , Paassen AH .C. van, and Maziarz, A (2004). Modelling the double faade withplants. In preration.Stee, W , Paassen AH.C . van. (2002). Validation of the simulation model of the double skinfaade . ABT 2002 Congress, Hong Kong .Weitzmann , P.Sasis Kalagasidis, A , Rammer Nielsen, T. , Peuhkuri , R. , and Hagentoft,C.(2003). Presentation of the international building physics tooibox for Simulink. EightInternationallBPSA Conference , Eindhoven, Netherlands.

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Appendix 1The best concept IDeltaClimat"For a specific new building the consortium of Rollecate (manufacturer of facades) and Unica(instalier of HVAC) a concept was designed that could compete with respect to costs with aconventional solution. The design "DeltaClimat" was analyzed using the simulation resultsas discussed in this paper. The reference building has a 40 % double glass area with asolarprotection factor G=0.36 (G is similar with ZTA). The installation consists of a centralbalanced ventilation system with heat recovery and a in each room an induction system inthe ceiling for heating and cooling .Especially the control system originally designed for the DeltaClimat system had to besimplified to approach the costs of the reference system . This could be realized withoutcompromising savings in energy costs. It could be kept at 38% .There are three components th at can be controlled - position of the ventilation windows -position of the radiator valve - central air handling installation supplying cooled air (16C) .The system can be described by various modes of contro/ (see a/so figure A 1): winter mode. Heating is supplied by radiators controlled by thermostatic valves. Freshair is supplied in a natural way and controlled by positioning the openings of the ventwindows in dependence of the wind speed to avoid too much ventilation . At low windspeed and too low outside temperatures the fan of the central installation is switched onin order to supply preheated air. By the resulting overpressure and the windowventopenings at minimum position the room air is forced to leave the room through thecavity of the double faade. This gives a kind of heat recovery, because the warm roomair heats the cavity and reduces by doing so the transmission losses. In order to reducecosts the possibility to make an under pressure in the rooms was omitted. Unfortunately,th is includes that the possibility to preheat ventilation air from the cavity by solarradiation is not used. moderate summer day. HVAC units are not in operation; the air valve in the supply unitis closed and window openings are controlled to keep the temperature below 24 C.Now the indoor climate is controlled in a passive way. Window positions are notcontinuously controlled. This would be too disturbing. By feed forward control they areput in proper positions at proper moments (8.00 , 12 .00 , 16.00 and 18 .00 o'clock). warm summer day. If the inhabitants are not satisfied with the resulted temperaturesthey can ask for cooling by activating the room controller that will open the valve in

order to supply cold air of 16 C. From now on air from the room is exhausted throughthe window openings to the cavity. This colder exhaust air will cool the cavity and theinner glass surface with the consequence that the comfort is improved. It is emphasizedthat in the DeltaClimat concept people take themselves the decision for mechanicalcooling. With the new adaptive comfort criteria in mind, that allows higher temperaturesin summer when windows can be opened, it is expected that people will use the coolingmode of control less frequently. This will reduce further the energy consumption forcooling.

Summer night. If required windows will be opened during the night in order to cooldown the building. A kind of predictive algorithm is applied. It says: "if during the daythe indoor temperature was above 25C then the first time th is happens the building willbe cooled down during the night to 22 C. If the next day this again is the case then it iscooled down to 20 C etc.". In this way night cooling anticipates on a coming warmperiod. If the weather changes the night cooling setpoint will increased gradually again.

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South

South

~ 1 7 IJ

South

o

South

winter

;--;;or;(

Moderate summerday:No cooled air.Co ol ing by na tHai ve nt il at ion on Iy

- - - - - - - - ' (

Hot summer day: centra lIy cooled air is supplied (onrequest) an d cavity is cooled by exhaustair.

;---1S"C[V]....., ....., 1 1 25 " C ( ( (

((

Nigh t cool ing (pre cooli ng bui Idi ng duri ng nig ht)

o 024naar 18 0

North

North

North

North

j2 4 ___

= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = ~ i

Figure A1. Modes of control of DeltaClimat concept (Rol/ecate-Unica)37


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Het belang van drukvereffening bij dubbelfaades

Prof. ir Nico Hendriks,capaciteitsgroep Fysische Aspecten van de Gebouwde Omgeving (FAGO),faculteit Bouwkunde, TU Eindhoven;directeur BDA Geveladvies B.V. , Gorinchem

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SynopsisDrukvereffening speelt een essentile rol bij een duurzaam goed functionerende gebouwschil. Dat is al heel lang bekend. Het binnendringen van regenwater, onder invloed van wind(driving rain) wordt er aanzienlijk door beperkt. Een ander voordeel is dat de windbelastingop het regenscherm door drukvereffening sterk kan worden gereduceerd. Toch bieden devoorschriften nauwelijks mogelijkheden van dit verschijnsel effectief gebruik te maken. Datkomt omdat nog steeds niet goed bekend is hoe drukvereffening precies in rekening gebracht moet worden.Dit artikel beschrijft de functie van drukvereffening in een twee-schalige constructie (pressu-re equalization rainscreen , vaak aangeduid als PER) en de opzet van promotieonderzoekaan de TUle dat er op is gericht meer kwantitatief inzicht te verkrijgen in de parameters diehet effect van drukvereffening bepalen. Hierbij wordt aandacht gegeven aan de meest problematische onderdelen van de gevel, namelijk de hoeken en de dakranden. Het uiteindelijke doel is om zodanige kennis en instrumenten te ontwikkelen dat optimale drukvereffenende twee-schalige constructies ontworpen kunnen worden.

1 InleidingDrukvereffening houdt in dat wanneer er een drukverschil heerst over een scheidingsconstructie (gevel of dak), het effect daarvan geminimaliseerd kan worden door drukvereffening.Voorwaarde voor drukvereffening is dat zich in de constructie een spouw bevindt die inverbinding staat met de buitenlucht, terwijl de scheiding naar de binnenruimte (vrijwel) luchtdicht is . De mate (eigenlijk de snelheid) van drukvereffening hangt onder meer af van deperforatiegraad van de scheiding naar de buitenlucht. De precieze modellering van drukvereffening is onderwerp van promotieonderzoek bij FAGO. Bij een goede drukvereffening is erbij een gecombineerde regen-wind aanval op de scheidingsconstructie (ook wel 'driving rain'genoemd) vrijwel geen drijvende kracht die het regenwater in de constructie perst. Daarmeewordt de basis gelegd voor een betrouwbare waterdichtheid. Bovendien biedt drukvereffening de mogelijkheid de windbelasting beter te verdelen over de twee buiten- en binnenschaai van de gevelconstructie.Welke mate van drukvereffening effectief kan worden bereikt hangt af van diverse, complexsamenhangende karakteristieken van de gevelconstructie (bijvoorbeeld penetratiegraad vande buitenschaal, volume van de luchtspouw, luchtdoorlatendheid van de binnenschaal ,stijfheid van de buitenschaal , vorm van de gevelopeningen), maar ook van de variatie in debuitendruk in plaats en tijd.

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2 Oorzaken van vochtindringing (Hendriks 2004)Figuur 1 toont de belangrijkste fysische oorzaken van het binnendringen van regenwater ineen gevel.

LZWAARTEKRACHT CAPILLAIR

CAPILLAIRE STUWDRUK

KINETISCHE ENERGIE DRUKVERSCHILFiguur 1. Belangrijkste fysische oorzaken van het binnendringen van vocht in een gevel

ZwaartekrachtBij open verticale voegen stroomt het water langs de voegwanden en verspreidt zich daarbijook naar de binnenzijde van de voeg. Bij horizontale voegen kan het langs de gevel stro-mende water langs de voegwanden in de voeg worden geleid.Capillaire krachtenDeze spelen een rol bij spleten met een breedte tussen 0,01 mm en 0,5 mmoKinetische energieIndien de regen niet verticaal valt (slagregen, driving rain), hebben de druppels kinetischeenergie in horizontale richting. Ze kunnen daardoor over enige afstand in open verticalevoegen binnendringen, ook als de lucht in deze voegen stil staat.

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DrukverschilDe belangrijkste oorzaak van het binnendringen van regen in een niet-afgedichte voeg (enin hef algemeen in een gevel) is het luchtdrukverschil tussen de buitenzijde (hoge druk) ende binnenzijde (lagere druk) van de voeg. De verschijnselen die optreden zijn afhankelijkvan de hoeveelheid water die langs de gevel stroomt, de breedte van de voegen en hetoptredende drukverschil.a. Bij smalle voegen kan het langs de gevel stromende water een gesloten film voor devoegopening vormen. Dit water wordt ten gevolge van het luchtdrukverschil in de voeggeperst. Als de voeg smal genoeg is in vergelijking met de hoeveelheid langs de gevelstromend water kan hierdoor een constante waterstroom in of door de voeg optreden.b. Bij wijde voegen zal het langs de gevel stromende water voor de voegopening geengesloten waterfilm vormen. Het luchtdrukverschil heeft dan een luchtstroom door devoeg tot gevolg, waardoor water, dat zich bij de opening van de voeg of aan de voegwand bevindt, verder de voeg in wordt getransporteerd.c. Bij voegen waarvan de breedte ligt tussen die welke hierboven zijn beschreven, kunnenbeide genoemde verschijnselen afwisselend optreden.De afdichtingssystemen waarbij voorzieningen zijn getroffen om de vier genoemde oorzakenvan het binnendringen van regen in een voeg op te heffen en waarbij tevens wordt afgedichttegen wind, zijn te verdelen in enkelvoudige en tweevoudige afdichtingssystemen.Het principe waarop deze indeling berust is in Nederland reeds lang bekend voor buitenwanden. Massieve wanden fungeren als afscherming tegen zowel regen als wind. Eenluchtdrukverschil p = Pe - Pi tussen de buitenzijde en de binnenzijde van de wand zal bij deopeningen direct aanleiding zijn tot het binnendringen van water.Bij wanden met een spouw is er een scheiding van functies: de buitenschaal fungeert alsregenkering, de binnenschaal als winddichting. De spouw heeft meerdere taken . De verbinding met buitenlucht heft het luchtdrukverschil over het buitenblad op (Pe = ps) , zodat eenbelangrijke oorzaak voor het binnendringen van regen is weggenomen. Dit noemt mendrukvereffening. Tevens dient de spouw voor de afvoer van de eventueel nog kleine hoeveelheid binnengedrongen water. Doordat het binnenblad droog of nagenoeg droog blijft, isde enige maar wel essentile functie daarvan het afdichten tegen wind die het luchtdrukverschil p = ps - Pi veroorzaakt.Drukvereffening werkt alleen wanneer de binnendichting (vrijwel) luchtdicht is.

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3 Drukvereffenende twee-schalige gevelconstructieHet principe van een drukvereffenende twee-schalige gevelconstructie (PER gevel) is weergegeven in figuur 2 (Li 2003).

Building Exterior

Wind Driven Rain

RainscreentI TotaJ venting area2) Venting lecatien3) Venting dlmensien4) Rainsaeen design laads5) Rainsaean stiffness

Air Barrier SystemtI Effectlve leakage area2) AIr barrier design Ioads31 Air barrier stiffness41 AIr barrier fasteners

Pressure EqualizationCavitytI Cavity deplh2) Compartmelll size31 Design leads on saais

Figuur 2.Principe van een drukvereffenendefwee-schalige gevelconstructie

Invloedsfactoren regenscherm(rainscreen):1) Total venting area=perforatiegraad van de buitenschaai

2) Venting location=plaats van de gevelopeningen3) Venting dimension=afmeting en vonm van degevelopeningen4) Rainscreen design loads=ontwerpbelasting op de buitenschaai5) Rainscreen stiffness=stijfheid van de buitenschaal

Invloedsfactoren drukvereffenende luchtspouw(Pressure equalization cavity):1) Cavity depth = spouwbreedte2) Compartment size = afmetingen van het compartiment3) Design loads on sealings = ontwerpbelasting op afdichtingenInvloedsfactoren binnenschaal(winddichting, air barrier system):1) Effective leakage area =effectieve doorsnede (lucht)lekken2) Air barrier design loads = ontwerpbelasting winddichting3) Air barrier stiffness = stijfheid binnenschaal4) Air barrier fasteners = bevestigingsmiddelen binnenschaalDe meest kritische plaatsen van de gevel ten aanzien van de effecten van drukvereffeningzijn die langs de hoeken en dakranden. Niet alleen kan hier de regen-wind intensiteit heelhoog zijn (Surry e.a. 1994, Van Mook 2002, 810cken en Carmeliet 2000), ook verandert deluchtdruk snel van positief aan de loefzijde naar negatief om de hoek of dakrand.Dit is weergegeven in Figuur 3 (Gerhardt en Janser 1994).

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cp "';

-c,

! ~ ~ IJ ,! ' I ,I:-I1I

c p. ,,..externer OruckbcfWcrl

n iemer DruckberNCr1

rCSultlerender Druckberwer1

Figuur 3, Schematische weergave van luchtstroming rondom de gevelhoek bi j een tweeschalige ge-velconstructie, waarbij de luchtspouw in verbinding staat met de buitenlucht,Het is duidelijk dat wanneer de luchtspouw om de gevelhoek gewoon doorloopt, er daargeen substantile drukvereffening kan plaatsvinden . Zonder speciale maatregelen betekentdit een aanzienlijk risico van vochtindringing . Bovendien kan de negatieve windbelasting aande lijzijde bij harde wind zeer aanzienlijk zijn en tot schade leiden, Tijdens de storm in oktober 2002 heeft zich dit bij een aantal plaatgevels voorgedaan (Figuur 4), De windsnelhedentijdens die storm waren overigens nog beduidend lager dan waarop gevelconstructies berekend moeten zijn . Zowel vochtindringing als windbelasting op de hoeken van eenpermeabele twee-schalige gevelconstructie kunnen sterk beperkt worden door plaatselijkeafsluiting van de luchtspouw,

Figuur 4, Windschade aan plaatgevel

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Ondanks het feit dat dit soort effecten al heel lang bekend zijn, zijn de ontwerprichtlijnen opdit punt nog steeds vrijwel alleen kwalitatief. AI in 1994 stelde Gerhardt voor de windcodeaan te passen. Zijn voorstellen zijn ook toegepast in het ontwerp van de dubbelfaade vanhet 'Stadttor Dsseldorf'- gebouw. De permeabiliteit van de buitenschaal is zodanig gekozendat de ontwerp windbelasting - althans naar de mening van Gerhardt - ongeveer 50/50verdeeld worden oven het regenscherm en de winddichte binnenschaal (respectievelijk -1,28 kN.m -2 en 1,1 kN .m-2) . Toch zijn deze voorstellen nog in geen enkel voorschrift overgenomen, om de eenvoudige reden dat zij naar de mening van andere deskundigen teveel zijngebaseerd op 'gevoelsmatige' aannamen. Enig empirisch bewijs is inmiddels in zoverregeleverd dat zich met de betreffende gevel geen problemen hebben voorgedaan.

4 ModelleringInmiddels wordt al jaren gewerkt aan verbetering van de modellen. Belangrijke onderzoekers op dit terrein zijn behalve Gerhardt, Inculet (Inculet en Davenport 1994, Inculet e.a.1997, Inculet en Surry 1999), Straube (1994, 1998), Suresh Kumar, Stathopoulos, VanSchijndel en Wisse (1998, 1999 en 2003). De basis voor al deze modellen is nog steeds de'Helmholtz Resonator Theory', wat een speciale vorm is van de 'Helmholtz resonator', zoalsbekend uit de akoestiek. Het principe hiervan is weergegeven in figuur 5.

x

Figuur 5. Helmholtz Resonator modelIn het model wordt verondersteld dat de kanten van de opening scherp zijn, de lucht samendrukbaar is en het een adiabatisch proces betreft.Tegenwoordig is het rekenen met modellen een stuk eenvoudiger geworden door de beschikbaarheid van zeer geavanceerde software en is het mogelijk uit te gaan van veel complexere parameters. Het betekent echter wel dat er dan veel meer bekend moet zijn over heteffect van bepaalde parameters zoals vorm en afmetingen van de openingen. Dergelijkonderzoek vormt een belangrijk element in lopend promotieonderzoek aan de TU/e (Li 2003,Li en De Wit 2004).

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5 Onderzoek aan de TUleDe meeste studies voor de validatie van modellen zijn gebaseerd op windtunnel of laboratorium experimenten. Het 'schalen' van een PER-gevel in een wind tunnel vormt echter eengroot probleem. Experimenten op ware grootte verdienen daarom de voorkeur. Niet alleengeven ze een beeld van de werkelijkheid, ook de schaalproblemen van wind tunnelproevenworden gelimineerd. Ze zijn dan ook essentieel voor de ontwikkeling en validatie van modellen.De TUle beschikt over een unieke meetopstelling voor windexperimenten op ware grootte .Bovendien is met die opstelling inmiddels veel ervaring opgedaan bij vorige succesvollepromotieonderzoeken van Geurts (1997) , Suresh Kumar (1997) en Van Mook (2002).Als referentie voor het onderzoek van Li wordt uitgegaan van de metingen uit 1997 (SureshKumar 2000). Bij dit experiment werd de waterindringing niet gemeten en werden de metingen alleen gedaan aan n paneel in het midden van het gebouw (het hoofdgebouw op decampus van de TUle) .Bij het onderzoek van Li worden de experimenten uitgevoerd aan de NW-hoek op de 1Odeverdieping. Harde wind komt voornamelijk uit westelijke richting en in die richting bevindenzich bijna alleen lage gebouwen. Dit betekent dat de meetlocatie zeer geschikt is voor hetmeten van windprofielen, 'driving rain ' en de effecten van drukvereffening. Figuur 6 toont demeetlocatie.

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Vier testpanelen zijn rond de gevelhoek in de gevel gemonteerd, zoals te zien op Figuur 7.

Figuur 7. Testpanelen rondom gevelhoek

In de testpanelen bevinden zich zowel dichte cirkelvormige meetplaten als meetplaten voor-zien van sleuven. Deze meetplaten zijn draaibaar en uitwisselbaar. Op deze manier kunnenzowel het aantal openingen, de stand als de vorm van de openingen gevarieerd worden . Detwee typen meetplaten worden getoond in de Figuren 8 en 9.

Figuur 8. Meetplaten met sleuven

Figuur 9. Meetplaten zonder sleuf

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6. ConclusieHet doel van de metingen is het verzamelen van betrouwbare data voor de verdere ontwikkeling van een voorspellend model. Hierbij zullen diverse parameters systematisch wordenonderzocht, zoals afmetingen van de compartimenten , aantal, plaats, afmetingen en vormvan de openingen. In de (hopelijk niet al te verre) toekomst zullen de resultaten informatieopleveren ter verbetering van de rekenmodellen in de betreffende voorschriften voor hetontwerpen van duurzaam functionerende drukvereffenende twee-schalige gevelconstructies.

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Literatuur1. Hendriks, NA. Dictaat Gevels en Daken, deel 1: Gevels, Technische Universiteit Eindhoven, Eindhoven , 2004.2. U, C. Wind loading and water penetration on pressure equalized ra inscreen walls, supportingpaper for the evaluation presentation of PhD study, Eindhoven University of Technology, 2003.3. U, C., Wit, M. de. Pressure equalization : The full-scale experiment in Eindhoven, paper to bepublished in 2004.4. Gerhardt HJ , Janser, F. Wind loads on wind permeable faades, Joumal of Wind Engineering andIndustrial Aerodynamics, 53:37-48, 1994.5. Inculet, DR . Pressure-equalization of ra inscreen cladding. M.E.Sc. Thesis, Faculty of EngineeringScience, The University of Western Ontario, Canada, 1990.6. Surry, D. , e.a. Wind, rain , and the building envelope: a status report of ongoing research at theUniversity of Western Ontario , Joumal of Wind Engineering and Industrial Aerodynamics; 53 :19-36 , 1994.7. Straube, JF. Moisture control and enclosure wall systems. PhD. Thesis , Civil Engineering Department, Un iversity of Waterloo, Canada, 1998.8. Straube, JF, Bumett, EFP. Performance measurement of pressure-moderated screened wallsystems, ICBEST Proceedings, Singapore, 1994.9. Schijndel, AWM van, Schols SFC. Modelling pressure equalization in cavities, Joumal of WindEngineering and Industrial Aerodynamics , 74-76:641-9, 1998.10 . Inculet, DR , Davenport, AG. Pressure-equalized rainscreens: A study in the frequency domain.Joumal of Wind Engineering and Industrial Aerodynamics, 53 :63-87 ,1 994.11. Suresh Kumar, K, Schijndel, AWM van. Cavity pressure dynamics of rainscreen walls. In : Proceedings of the 4th UK Conference on Wind Engineering, Bristol , UK, 1998.12 . Suresh Kumar, K, Wisse, JA. A full-scale study on pressure equalization of rainscreen facades ,proceedings 10th International Conference on Wind Engineering, Copenhagen, June 1999.13 . Suresh Kumar, K, Stathopoulos , T, Wisse, JA. Field measurement data of wind loads on rainscreen walls , Joumal of Wind Engineering and Industrial Aerodynamics 91: 1401-1417, 2003.14 . Inculet, D., Surry, D. The influence of unsteady pressure gradients on compartmentalization Requirements for Pressure-Equalised Rainscreen, BLWT-SS37-, the University of Western Ontario,1996.15 . Inculet, D., e.a. Unsteady pressure gradients and their implications for pressure-equalised rainscreens, Proceedings of the International Conference on Building Envelope Systems and Technol

ogy, Bath, April 1997.16 . Inculet, D., Surry, D. , Optimum vent locations for partially-pressurised rainscreens, Wind Engineering into the 21 st Century, p.1131-1136. Balkerna, Rotterdam 1999.17 . Mook, FJR. Driving rain on building envelopes. PhD. thesis , Eindhoven University ofTechnology,2002.18 . Botterna , M. Wind climate and urban geometry. PhD thesis, Eindhoven University of Technology,January 1993.19 . Geurts, CPW. Wind induced pressure fluctuations on building facades. PhD thesis, EindhovenUniversity ofTechnology, June 1997.20 . Choi , ECC. Simulation of wind-driven-rain around a building . Joumal of Wind Engineering andIndustrial Aerodynamics, 46/47: 721-729, 1993.21 . Blocken, B, Carmeliet, J. Driving ra in on bu ilding envelopes - I. Numerical estimation and full-scaleexperimental verification, Joumal of Thermal Envelope and Building Science, Volume 24, Issue 1:

61-84, 2000.22 . Blocken, B, Carmeliet, J. Driving rain on building envelopes - 11 . Representative experimental datafor driving rain estimation , Joumal of Thermal Envelope and Building Science, Volume 24, Issue 2:89-110, October 2000.23 . Molen MK van der, e.a. Sonic anemometer (co)sine response and flux measurement: 11. The effectof introducing an angle of attack dependent calibration , Agricultural and Forest Meteorology, Volume 122, Issues 1-2: 95-109, 2004.

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Operationele prestaties van dubbele gevels als ontwerpopgave

Dr.lng.Just RenekensTU -Delft Bouwkunde, Faade TechnologieGeveltechnisch bureau Renckens Advies bv te Nijmegen

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InleidingDe tweedehuidgevel is een type dubbelschalige gevel met geventileerde spouw, waarinopgenomen een zonwering. De klimaatgevel is een ander concept dat hieraan ook voldoet.Er zijn nog een aantal afgeleide gevelconcepten die op een zelfde wijze ingericht zijn.Bij deze gevelconcepten vervult de spouwzonwering een belangrijke energetische functie,naast de door de gebruiker hiermee te regelen uitzicht- en daglichtcondities.Er bestaat in deze een belangenconflict tussen energie-efficintie- en comfortaspecten.In deze bijdrage wordt daarop ingegaan. Alsmede op het ontwerpen en bouwen gebaseerdop operationele prestaties.

Dubbelschalige geventileerde gevels met spouwzonweringDit type glasgevel is opgebouwd uit een binnengevel met op spouwafstand een buitengevel.De spouw wordt mechanisch of natuurlijk geventileerd. In de spouw is een zonweringgeplaatst, meestal een instelbare horizontale lamellenzonwering. Maar ookscreendoekzonweringen komen voor. In bijna alle gevallen is ervoor gezorgd dat dezonwering aan de buitenzijde een zonnestralingreflecterende oppervlakteafwerking heeft.De twee meest voorkomende dubbele glasgevels zijn (Figuur 1): De klimaatgevel , ook wel de actieve gevel genoemd. Gevelopbouw: thermischgesoleerde buitengevel, smalle spouw (circa 200 mm) waarin opgenomen eeninstelbare zonwering, de spouw wordt mechanisch geventileerd met ruimtelucht, en eenenkelglas binnengevel. Te-openen-ramen passen eigenlijk niet in dit gevelconcept,maar komen wel voor. De tweedehuidfaade, ook wel interactieve gevel genoemd. Gevelopbouw: thermischgesoleerde binnengevel, een buitenspouw waarin opgenomen een instelbarezonwering, de spouw is vaak gecompartimenteerd en wordt per compartiment natuurlijk

geventileerd met buitenlucht via spouw luchttoevoer- en afvoeropeningen,spouwbreedte meestal circa 600 mm , en een enkelglas buitenschil. In de binnengevelzijn vaak te-openen-ramen opgenomen.In beide gevallen wordt de zonwering meestal elektrisch aangedreven en aangesloten aanhet gebouwbeheersysteem (GBS). De gebruiker kan vaak de centraal geregelde instellingvan de zonwering 'overrulen' .De energetische prestatiesDubbelschalige glasgevels worden gekozen om te bereiken dat bij: een hoog percentage doorzichtbeglazing kleur neutrale isolerende beglazing met relatief veel daglichtdoorlaat en als buitenzonwering niet gewenst istoch te voldoen aan de energieprestatie-eisen. Bij de tweedehuidfaade speelt het imagovan dit glasgevelprincipe ook een rol.De keuze kan ook ingegeven zijn vanwege de gunstige geluidsisolatie-eigenschappen vandubbele gevels.Door toepassing van low-e-beglazing (lage emisiviteitscoating meestal op zijde 3) eneventueel argongasvulling van de spouw van de isolerende beglazing kan worden voldaanaan lage U-waarde-eisen van de gevel. Ten opzichte van de enkelschalige gevel is de Uwaarde van dubbelschalige gevels gunstiger.

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f I

tLifiguur 1enkelschaligdubbelschalig: actiefsingle layer

dubbelschalig: interactiefdouble layer: interactive double layer: active

energy efficient slat position(!':hadow and rAflAr.tion(, ~ ~ ' " . leakBge direct radiation~ / ' i natura! ventilation

fiQuur2

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In alle gevallen geldt ten aanzien van de zonwering bij zonbelasting voor een te realiserenlage g-waarde: zonwering neer en volledig schaduwgevend; zonweringlamellen met aan de buitenzijde een reflecterende (aluminiumkleurige)oppervlakteafwerking geplaatst in een naar buiten reflecterende stand vanzonnestraling; voldoende luchtstroom langs de lamellen.Zodoende worden g-waarden bereikt van 0,15 of lager, hetgeen een energie-efficintuitgangspunt inhoudt (verlaging van de koellast) . Echter door de energetisch gunstigeinstelling van de zonwering worden uitzicht en daglichttoetreding beperkt!

De comfortprestatiesDubbelschalige glasgevels worden dus gekozen als helder doorzicht vereist wordt en geenbuitenzonwering toegestaan is . Door de toegevoegde gevelschil , plaatsing van dezonwering in de spouw en ventilatie van de tussenruimte, worden ongeveer dezelfde gwaarden (ZTA-waarden) bereikt als bij vergelijkbare enkelschalige glasgevels met goedfunctionerende buitenzonwering.De tweedehuidfaade is bovendien architectonisch modern.Dubbelschalige gevels leveren ten opzichte van enkelschalige gevels een hogeregeluidsisolatie. De tweedehuidfaade maakt het mogelijk nagenoeg weeronafhankelijk(enige) natuurlijke ventilatie door openstaande ramen te verkrijgen . De klimaatfaade is 'swinters comfortabel omdat koudelast vanuit de gevel niet optreedt.Deze aspecten dienen het gebruikscomfort.De gebruiker heeft geen weet van de belangrijke energetische functie van despouwzonwering als de zon op de gevel schijnt. Wel dat naar individuele normen de meestalcentraal geregelde zonwering de daglichttoetreding en het uitzicht benvloedt, meestal nietconform de wensen van de gebruikers. Hij/zij ergert zich dan ook vaak aan de centraleregeling van de stand van de zonwering. Figuur 2.Daglicht- en uitzichtcomfort harmoniren meestal niet met energie-efficintie belangen.Dit verschijnsel is in mindere mate ook van toepassing ten aanzien van het gebruik van teopenen-ramen.In veel gevallen wordt er een compromis bereikt door primair de sturing van de zonweringte regelen via het GBS . En secondair de gebruiker de mogelijkheid te bieden de instelling te'overrulen' en naar eigen wens te regelen. Meestal wordt er dan op werkdagen centraal eenpaar maal per dag 'geveegd', bijvoorbeeld 12 .30 uur, 19.00 uur en 07 .00 uur, waarbijwaarnodig de energie-efficinte stand van de zonwering hersteld wordt. Zodoende bereiktmen dat gebruikerscomfort op de eerste plaats komt, dat is gunstig voor het welbehagen ende productiviteit, maar dat als het strookt of als de gebruikers niet aanwezig zijn, de energieefficintie van het actieve/interactieve gevelconcept gewaarborgd wordt.

De facilitair manager, de gebruikerBij de ingebruikname van de gebouwruimten wordt de laatste hand gelegd aan de inregelingvan het GBS . In die fase wordt vaak het oorspronkelijke protocol voor de aansturing van despouwzonwering gewijzigd naar inzichten en wensen van het facilitair bedrijf en degebruikers. En daarbij bestaat het risico dat aan het zonne-energie-beheersingsconceptgeweld gedaan wordt.Doordat vooral gebruikers het energetisch principe van de dubbele gevel niet begrijpen enhet facilitair management in de eerste plaats gericht is op gebruikerstevredenheid, zien wedat de inspanningen om met name een lage g-waarde te realiseren , mede in het kader vande EPN , in de praktijk onvoldoende gerealiseerd worden. Indien het energieconcept van de

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gevel voorrang krijgt ten opzichte van het comfortconcept, en dit met name ten aanzien vande stand van de zonwering bij zonbelaste gevels, dan ontstaan in principe belangenconflicten.

PraktijkvoorbeeldenABNAmro hoofdkantoor te AmsterdamKlimaatgevels.De kamerhoge klimaatglasgevel is verdeeld in een bovenzone, een zichtzone en eenborstweringszone. Elke zone heeft een eigen elektrisch bedienbare horizontalelamellenzonwering aangesloten aan het GBS .De ontwerpuitgangspunten waren:De zonweringen worden centraal steeds neergelaten, de lamelhoek wordt in schaduw- enzonnestraling reflecterende stand gesteld (circa 45).De zichtzonezonwering kan door de gebruiker overruled worden.Echter er wordt centraal 'geveegd' om circa 12.00,18.00 en 22 .00 uur.Praktijk na ingebruikname:Alle zonweringen kunnen door de gebruiker 'overruled' worden en alleen centraal 'vegen'om 18.00 en 22.00 uur. Figuur 3.Hierdoor is het energieverbruik voor koeling hoger dan voorzien.Maar de gebruiker is tevreden!

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