CHAPTER IV - AAAMSA
CHAPTER IVSelectionofGlazing MaterialsAugust 2012
ASSOCIATION OF ARCHITECTURAL ALUMINIUM MANUFACTURERS OF SOUTH AFRICATrading as the AAAMSA GroupRegistration #: 1974/00006/08Association Incorporated under Section 211ST Floor, Block 4Conference Centre2nd RoadMidrand1685P O Box 7861HALFWAY HOUSE1685 (011)805-5002Fax:(011)805-5033e-mail: aaamsa@iafrica.comadditional e-mail: sagga@aaamsa.co.zaweb-site: www.aaamsa.co.zaACKNOWLEDGEMENTSAluminium Verlag – DüsseldorfFensterbau mit Aluminium – Walter SchmidtAmerican Architectural Manufacturers AssociationMetal Curtain Walls/Windows and Sliding Glass Doors/Aluminium Store Front and Entrances/Skylights and SpaceEnclosuresASTM International E1300Koninklijk Technicum PBNAStaalcontructies 43A.VRSouth African Bureau of StandardsSANS 10160, SANS 10137, SANS 10400, SANS 204, SANS 613 and SANS 549Southern African Institute of Steel ConstructionSouthern African Steel Construction HandbookVerlag Stahleisen M.B.H. DüsseldorfStahl im HochbauBuilding Code AustraliaBCA 2007 Volume 1 & 2W.W. Norton & CompanyWindow Systems for High Performance BuildingsLawrence Berkeley National LaboratoryTherm/Windows/Resfen/OpticsNational Fenestration Rating CouncilProcedure ManualsNote: This Selection Guide replaces the following AAAMSA Publication which is hereby withdrawn in its entirety:Selection Guide for Glazed Architectural Aluminium Products – Introducing Energy Efficiency in Fenestration– June 2008Any information contained in Selection Guides of earlier dates, which contradicts with data contained in this manual,is information superseded by this publicationAAAMSA – April 2012DISCLAIMERAll information, recommendation or advice contained in this AAAMSA Publication is given in good faith to the best of AAAMSA’sknowledge and based on current procedures in effect.Because actual use of AAAMSA Publications by the user is beyond the control of AAAMSA such use is within the exclusiveresponsibility of the user. AAAMSA cannot be held responsible for any loss incurred through incorrect or faulty use of itsPublications.Great care has been taken to ensure that the information provided is correct. No responsibility will be accepted by AAAMSA forany errors and/or omissions, which may have inadvertently occurred.This Guide may be reproduced in whole or in part in any form or by any means provided the reproduction or transmissionacknowledges the origin and copyright date.Copyright AAAMSA 2012Page 3
4.SELECTION OF TYPES OF GLAZING MATERIALS4.1INTRODUCTIONGlass and plastic glazing are usually selected on merits of economics, aesthetics and performance but all glazing is to beexecuted in strict accordance of the latest editions of the following South African Standards:National Building Regulations Part N - GlazingSANS 10137 - Code of Practice for the Installation of Glazing Materials in BuildingsSANS 10400: Part N - The Application of the National Building Regulations – GlazingSANS 10400:Part XA – The Application of the National Building Regulations – Energy Efficiency in BuildingsSANS 1263 - Safety and security glazing materials for buildingsPart ISafety performance of glazing materials under human impactPart IIBurglar-resistance and vandal resistant glazing materialsPart IIIBullet-resistant glazing materialsSANS 204: Energy Efficiency in BuildingsFloat, toughened, laminated, wired and patterned glass is currently used in the building industry. Laminated safety glassis currently locally produced using the following manufacturing process.Laminated safety glass using poly-vinyl butyral (PVB) interlayer is supplied in three strengths namely NormalStrength (N.S.), High Penetration Resistance (H.P.R.) and High Impact (H.I.).Specifiers and manufacturers must ensure that the manufacturer of any laminated glass provides a warranty of not lessthan 5 (five) years against delamination and colour degradation, confirming that the product confirms to that section ofSANS 1263 which pertains to the particular application of safety glass i.e., for resistance to human impact (Part I) or toburglary and vandalism (Part II), or to firearms (Part III).Note!In terms of SANS 1263-Part 1 glass with applied film (organic coating) is not regarded as a safety glazingmaterial unless it meets all requirements of SANS 1263-Part I (including the boil and artificial ageing tests). Inaddition the applied film must cover the entire surface of the glazing material i.e. the film must be retained in theglazing rebate.General applications of glass typesConditionGlass and PlasticsHuman safety (SANS 1263 - Part 1)Laminated glass or toughened glass or polycarbonateSecurity (smash and grabs, riots, bombs, fire Laminated or multi-laminated or Bullet Resisting Glass orarms, petrol bombs etc.)polycarbonate (SANS 1263 Parts II and III)Heavy human traffic (i.e. Balustrades)Toughened Glass or polycarbonate (SANS 1263 Part I)Wired glass or laminated wired glass or laminated glass withFireintumescent interlayers or Borosilicate and calcium silicate glassUnframed applications (suspended assemblies,Toughened Glass or polycarbonate (SANS 10137)unframed doors, etc)Laminated or Wired glass (wired in the case where penetration ofglass or water ingress is not a problem) or toughened glass (onlyOverhead glazingpermitted when supported all round (SANS 10137) or acrylic orpolycarbonateLaminated glass or Sealed Insulated glass units or acrylic orSound ControlpolycarbonateTinted, reflective and or low-e glass or Sealed Insulated glassSolar Controlunits incorporating these or acrylic or polycarbonateCondensationSealed insulated glass units or acrylic or polycarbonateOne-way visionReflective glass or acrylic or polycarbonateUltra-Violet EliminationLaminated glass or acrylic or polycarbonateFish tanks DomesticAnnealed float glass (SANS 17) or acrylic or polycarbonateUnderwater Observation panelsMulti-laminated glass or acrylic or polycarbonateFloor & Stair treadsMulti-laminated glass or acrylic or polycarbonate4.2PERFORMANCE OF GLASS PRODUCTSAn important aspect of glass selection is the performance of glass in respect of its sound insulation, heat loss and heatgain properties. Although the discussion of the merits of these properties falls outside the scope of the Selection Guidesome guidance is provided to the specifier in the following paragraphs.Page 2
Due to the vast variety of glass and plastic types the specifier is urged to consult the manufacturer or competent person(glazing) to obtain the relevant technical glass and plastics specifications.4.3SOUND INSULATIONNOTE:1.i) Thickness for thickness, clear float, toughened, wired, coated and tinted monolithic glass products haveexactly the same acoustic performance.ii) Data provided is intended as a guide only. Due to the numerous possible computations, data is to beconfirmed with the glass and plastics manufacturer or competent person (glazing).SINGLE GLAZINGMonolithic GlassGlass thicknessRw Index (ISO 717)Laminated GlassGlass thicknessRw Index (ISO 717)2.4276296.383210338.38341741SEALED INSULATED GLASS UNITS (Double glazing)Monolithic glass and monolithic glassGlass/Space/Glass thickness4/12/4Rw Index (ISO 717)29Laminated glass and monolithic glassGlass/Space/Glass thicknessRw Index (ISO 717)3.6/12/6306.38/12/636DOUBLE WINDOWS (Secondary sash)Glass/Space/Glass thicknessRw Index (ISO 717)4.412346/150/44510/200/647ENERGY RELATED PROPERTIES OF WINDOWS4.4.1 PROPERTIES OF GLAZING THAT AFFECT ENERGY PERFORMANCE Figure 4.1: Solar radiation through a glazing material is reflected, transmitted or absorbedPage 3
Most window and façade assemblies consist of glazing and frame components. Glazing may be a single pane of glass (orplastic) or multiple panes with air spaces in between. These multiple layer units, referred to as insulating glazing units(IGU), include spacers around the edge and sometimes low-conductance gases in the spaces between glass panes.Coatings and tins affect the performance of the glazing. The IGU is placed within a frame of aluminium, steel, wood,plastic, or some hybrid or composite material. Some curtain wall systems using structural sealants and other specialfittings have no exterior frame.Heat flows through a window assembly in three ways: conduction, convection, and radiation. Conduction is heattravelling through a solid, liquid or gas. Convection is the transfer of heat by the movement of gases or liquids, likewarm air rising from a candle flame. Radiation is the movement of energy through space without relying on conductionthrough the air or by movement of the air, the way you feel the heat of a fire.When there is a temperature difference across an object (i.e., when a window separates a cold outdoors from a warminterior or a hot outside from a conditioned interior space), heat transfer will occur via these three physical mechanisms:conduction through glass and solid frame materials, convection/conduction through air spaces, and long-wave radiationbetween glass surfaces on either side of an air gap. This temperature-driven heat transfer is quantified by the term Ufactor and is discussed in the section on insulating value.There are two distinct types of radiation or radiation heat transfer:Long-wave radiation heat transfer refers to radiant heat transfer between objects at room or outdoor environmentaltemperatures. These temperatures emit radiation in the rage of 3-50 microns.Short-wave radiation heat transfer refers to radiation from the sun (which is at a temperature of 6000K) and occursin the 0.3-2.5 micron range. This range includes the ultraviolet, visible, and solar-infrared radiation (Figure 4.2)1.Idealized transmittance of a glazing with alow-E coating designed for low solar heatgain. Visible light is transmitted and solarinfrared radiation is reflected. Long-waveinfrared radiation is reflected back into theinterior. This approach is suitable forcommercial buildings in almost allclimates.2.Idealized transmittance of a glazing with alow-E coating designed for high solar heatgain.Visible light and solar-infraredradiation are transmitted.Long-waveinfrared radiation is reflected back into theinterior. This approach is more commonlyused for residential windows in coldclimates.Note: As shown by the solar spectrum in thefigure, sunlight is composed of electromagneticradiation of many wavelengths, ranging fromshort-wave invisible ultraviolet to the visiblespectrum to the longer, invisible solar-infraredwaves.Figure 4.2: Ideal spectral transmittance for glazing in different climatesEven though the physical process is the same, there is no overlap between these two wavelength ranges. Coatings thatcontrol the passage of long wave or solar radiation in these ranges, through transmission and/or reflection, can contributesignificantly to energy savings and have been the subject of significant innovations in recent years. Glazing types vary intheir transparency to different parts of the visible spectrum. For example, a glass that appears tinted green as you lookthrough it toward the outdoors transmits more sunlight from the green portion of the visible spectrum and absorbs orreflects more of the other colours. Similarly, a bronze-tinted glass absorbs or reflects the blues and greens and transmitsthe warmer colours. Neutral gray tints absorb or reflect most colours equally.The same principle applies outside the visible spectrum. Most glass is particularly transparent to at least some ultravioletradiation, while plastics are commonly more opaque to ultraviolet. Glass is opaque to long-wave infrared radiation butgenerally transparent to solar-infrared radiation. Strategic utilization of these variations has made some high-performanceglazing products. The four basic properties of glazing that affect radiant energy transfer-transmittance, reflectance,absorptance, and emittance – are described below.Page 4
4.4.2 TRANSMITTANCETransmittance refers to the percentage of radiation that can pass through glazing. Transmittance can be defined fordifferent types of light or energy, e.g., visible transmittance, UV transmittance, or total solar energy transmittance.Transmission of visible light determines the effectiveness of a type of glass in providing daylight and a clear viewthrough the window. For example, tinted glass has a lower visible transmittance than clear glass. While the human eye issensitive to light at wavelengths from about 0.4 to 0.7 microns, its peak sensitivity is at 0.55, with lower sensitivity at thered and blue ends of the spectrum. This is referred to as the photonic sensitivity of the eye.More than half of the sun’s energy is invisible to the eye. Most reaches us as near-infrared with a few percent in theultraviolet (UV) spectrum. Thus, total solar energy transmittance describes how the glazing responds to a much broaderpart of the spectrum and is more useful in characterizing the quantity of total solar energy transmitted by the glazing.With the recent advances in glazing technology, manufacturers can control how glazing materials behave in thesedifferent areas of the spectrum. The basic properties of the substrate material (glass or plastic) can be altered, andcoatings can be added to the surfaces of the substrates. For example, a window optimized for day lighting and forreducing overall solar heat gains should transit an adequate amount of light in the visible portion of the spectrum, whileexcluding unnecessary heat gain from the near-infrared part of the electromagnetic spectrum.4.4.3REFLECTANCEJust as some light reflects off of the surface of water, somelight will always be reflected at every glass surface. Aspecular reflection from a smooth glass surface is a mirrorlike reflection similar to the image of yourself you seereflected in a store window. The natural reflectivity of glassis dependent on the type of glazing material, the quality of theglass surface, the presence of coatings, and the angle ofincidence of the light. Today, virtually all glass manufacturedin the United States is float glass, which reflects 4 percent ofvisible light at each glass-air interface or 8 percent total for asingle pane of clear, uncoated glass. The sharper the angle atwhich the light strikes, however, the more the light isreflected rather than transmitted or absorbed (Figure 4.3).Even clear glass reflects 50% or more of the sunlight strikingit at incident angles greater than about 80 . (The incidentangle is formed with respect to a line perpendicular to theglass surface).Figure 4.3: Sunlight transmitted and reflected by 6mmclear glass as a function of the incident angleThe reflectivity of various glass types becomes especially apparent during low light conditions. The surface on thebrighter side acts like a mirror because the amount of light passing through the window from the darker side is less thanthe amount of light being reflected from the lighter side. This effect can be noticed from the outside during the day andfrom the inside during the night. For special applications when these surface reflections are undesirable (i.e., viewingmerchandise through a store window on a bright day), special coatings can virtually eliminate this reflective effect.Most common coatings reflect in all regions of the spectrum. However, in the past 20-years, researches have learned agreat deal about the design of coatings that can be applied to glass and plastic to preferentially reflect only selectedwavelengths of radiant energy. Varying the reflectance of far-infrared and near-infrared energy has formed the basis forhigh-performance low-E coatings.4.4.4 ABSORPTANCEEnergy that is not transmitted through the glass or reflected off its surfaces is absorbed. Once glass has absorbed anyradiant energy, the energy is transformed into heat, raising the glass temperature.Typical 6mm clear glass absorbs only about 7% of sunlight at a normal angle of incidence (also a 30 angle of incidence,as shown in Figure 4.3). The absorptance of glass is increased by glass additives that absorb solar energy. If they absorbvisible light, the glass appears dark. If they absorb ultraviolet radiation or near-infrared, there will be little or no changein visual appearance. Clear glass absorbs very little visible light, while dark-tinted glass absorbs a considerable amount(Figure 4.4).Page 5
Figure 4.4: Solar energy transmission through three types of glass under standard ASHRAE summer conditionsThe absorbed energy is converted into heat, warming the glass, thus, when “heat-absorbing” glass is in the sun, it feelsmuch hotter to the touch than clear glass. Tints are generally gray, bronze, or blue-green and were traditionally used tolower the solar heat gain coefficient and to control glare. Since they block some of the sun’s energy, they reduce thecooling load placed on the building and its air-conditioning equipment. The effectiveness of heat-absorbing singleglazing is significantly reduced if cool, conditioned air flows across the glass. Absorption is not the most efficient way toreduce cooling loads, as discussed later.All glass and most plastics, however, are generally very absorptive of long-wave infrared energy. This property is bestillustrated in the use of clear glass for greenhouses, where it allows the transmission of intense solar energy but blocks theretransmission of the low-temperature heat energy generated inside the greenhouse and radiated back to the glass.4.4.5 EMMITTANCEWhen solar energy is absorbed by glass, it is either converted away by moving air or reradiated by the glass surface. Thisability of a material to radiate energy is called its emissivity. Window glass, along with all other objects, typically emits,or radiates, heat in the form of long-wave far-infrared energy. The wavelength of the long-wave far-infrared energyvaries with the temperature of the surface. This emission of radiant heat is one of the important heat transfer pathwaysfor a window. Thus, reducing the window’s emission of heat can greatly improve its insulating properties.Standard clear glass has an emittance of 0.84 over the long-wave infrared portion of the spectrum, meaning that it emits84% of the energy possible for an object at room temperature. It also means that for long-wave radiation striking thesurface of the glass, 84% is absorbed and only 16% is reflected. By comparison, low-E glass coatings have an emittanceas low as 0.04. This glazing would emit only 4% of the energy possible at its temperature and thus reflect 96% of theincident long-wave infrared radiation.4.5DETERMINING ENERGY-RELATED PROPERTIES OF WINDOWSThere are four properties of windows that are the basis for quantifying energy performance:U-factor. When there is a temperature difference between inside and outside, heat is lost or gained through thewindow frame and glazing by the combined effects of conduction, convection, and long-wave radiation. The Ufactor of a window assembly represents its overall heat transfer rate or insulating value.Solar Heat Gain Coefficient. Regardless of outside temperature, heat can be gained through windows by director indirect solar radiation. The ability to control this heat gain through windows is characterized in terms of thesolar heat gin coefficient (SHGC) or shading coefficient (SC) of the window.Visible Transmittance. Visible transmittance (VT), also referred to as visible light transmittance (VLT), is anoptical property that indicates the amount of visible light transmitted through the glass. It affects energy byproviding daylight that creates the opportunity to reduce electric lighting and its associated cooling loads.Air Leakage. Heat loss and gain also occur by air leakage through cracks around sashes and frames of thewindow assembly. This effect is often quantified in terms of the amount of air (cubic meters per minute) passingthrough a unit area of window (square metre) under given pressure conditions.These four concepts – as well as Light-to-Solar-Gain ratio, a ratio of VT/SHGC – have been standardized within theglazing ind
SANS 10160, SANS 10137, SANS 10400, SANS 204, SANS 613 and SANS 549 Southern African Institute of Steel Construction Southern African Steel Construction Handbook Verlag Stahleisen M.B.H. Düsseldorf Stahl im Hochbau Building Code Australia BCA 2007 Volume 1 & 2 W.W. Norton &a
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