ASHRAE FUNDAMENTALS IP CH 15-2017 Fenestration.pdf

1、15.1CHAPTER 15FENESTRATIONFENESTRATION COMPONENTS 15.1Glazing Units . 15.1Framing . 15.2Shading 15.3DETERMINING FENESTRATION ENERGY FLOW 15.3U-FACTOR (THERMAL TRANSMITTANCE) 15.4Determining Fenestration U-Factors 15.5Surface and Cavity Heat Transfer Coefficients . 15.6Representative U-Factors for Do

2、ors . 15.13SOLAR HEAT GAIN AND VISIBLE TRANSMITTANCE 15.14Solar-Optical Properties of Glazing 15.14Solar Heat Gain Coefficient 15.19Calculation of Solar Heat Gain . 15.32SHADING AND FENESTRATION ATTACHMENTS 15.33Shading. 15.33Fenestration Attachments. 15.34VISUAL AND THERMAL CONTROLS . 15.52AIR LEAK

3、AGE . 15.53DAYLIGHTING 15.54Daylight Prediction 15.54Light Transmittance and Daylight Use 15.55SELECTING FENESTRATION 15.57Annual Energy Performance 15.57Condensation Resistance . 15.58Occupant Comfort and Acceptance . 15.60Durability . 15.61Supply and Exhaust Airflow Windows . 15.62Codes and Standa

4、rds 15.62Symbols 15.64ENESTRATION is an architectural term that refers to the ar-Frangement, proportion, and design of window, skylight, and doorsystems in a building. Fenestration can serve as a physical and/orvisual connection to the outdoors, as well as a means to admit solarradiation for dayligh

5、ting and heat gain to a space. Fenestration can befixed or operable, and operable units can allow natural ventilation toa space and egress in low-rise buildings.Fenestration affects building energy use through four basic mech-anisms: thermal heat transfer, solar heat gain, air leakage/ventilation/ex

6、change, and daylighting. Fenestration can be used to positively in-fluence a buildings energy performance by (1) using glazing andframing to minimize conductive heat loss, (2) using glazing and shad-ing strategies to control solar heat gain to supplement heating andminimize cooling requirements, (3)

7、 specifying low-air-leakage fen-estration products, (4) integrating fenestration into natural ventilationstrategies that can reduce energy use for cooling and outdoor air re-quirements, and (5) using daylight to offset lighting requirements.Todays designers and builders; minimum energy standards and

8、codes; green building standards, codes, and rating programs; andenergy efficiency incentive programs are seeking more from fenes-tration systems and giving credit for high-performing products.Window, skylight, and door manufacturers are responding with newand improved products to meet these demands.

9、 With the widespreaduse of simulation software, designing to improve thermal perfor-mance of fenestration products has become much easier. Throughparticipation in rating and certification programs that require the useof this software, fenestration manufacturers can take credit for theseimprovements

10、through certified ratings.A designer should consider architectural and code requirements,thermal performance, daylight performance, air leakage, energy andenvironmental impacts, economic criteria, and human comfort whenselecting fenestration. Typically, a wide range of fenestration prod-ucts is avai

11、lable that meet the specifications for a project. Refiningthe specifications to improve energy performance and enhance a liv-ing or work space can result in lower energy costs, increased produc-tivity, and improved thermal and visual comfort.1. FENESTRATION COMPONENTSFenestration components include

12、glazing material, either glassor plastic; framing, insulation, mullions, muntin bars, dividers, andopaque door slabs; and indoor and outdoor shading devices such aslouvered blinds, drapes, roller shades, lightshelves, metal grills, andawnings. In this chapter, fenestration and fenestration systemsre

13、fer to the basic assemblies and components of window, skylight,and door systems that are part of the building envelope.1.1 GLAZING UNITSMost fenestration currently manufactured using glass contains aglazing system that is packaged in the form of a glazing unit. A glaz-ing unit consists of two or mor

14、e glazing layers that are held apart byan edge seal. Figure 1 shows the construction of a typical double-glazing unit.The most common glazing material is glass, although polymer(plastic) is sometimes used, either in the form of intermediate filmsbonded to glass, or as stand-alone glazing material po

15、pular in someskylight products. Both may be clear, tinted, coated, laminated,The preparation of this chapter is assigned to TC 4.5, Fenestration. Fig. 1 Construction Details of Typical Double-Glazing Unit15.2 2017 ASHRAE HandbookFundamentals tempered, patterned, or obscured, and polymer types can be

16、 easilyshaped, textured, and profiled using several processing options.Clear glazing material transmits more than 75% of the incident solarradiation and more than 85% of the visible light. Body-tinted glasscontaining a pigment is available in many colors, all of which differin the amount of solar ra

17、diation and visible light they transmit andabsorb. Some coated glazing materials are highly reflective (e.g.,mirrors), whereas others have very low reflectance. Some spectrallyselective glazing products include coatings that have a visible lighttransmittance more than double their solar transmittanc

18、e; these aredesirable for good daylighting while minimizing cooling loads.Coatings that reduce radiant heat exchange are called low-emissivity(low-e) coatings. Laminated glass is made of two panes of glass ad-hered together. The interlayer between the two panes of glass is typ-ically plastic and may

19、 be clear, tinted, or coated. Tempered glass isdesigned for safety and shatters into pebble-sized pieces when bro-ken. Patterned glass is a durable ceramic frit applied to a glass sur-face in a decorative pattern. Obscured glass is translucent and istypically used in privacy applications.Low-e coate

20、d glass is energy efficient, improves daylighting po-tential, and enhances occupant comfort. Thus, it is now used in thevast majority of fenestration products. Low-e coatings are typicallyapplied to one of the protected internal surfaces of the glazing unit(surface #2 or #3 in Figure 1), but some ma

21、nufacturers now offerdouble- or triple-glazed products with an additional low-e coatingon the exposed room-side surface (surface #4 in Figure 1, or whatwould be #6 in triple glazing). Low-e coatings can also be applied tothin plastic films for use either as one of the middle layers in glazingunits w

22、ith three or more layers (stretched and held in place by aspacer system), or surface-applied film, where the exposed low-ecoating is protected by a very thin, thermal-IR (TIR) transparentprotective layer.A wide variety of low-e coatings are used today. Physically, theycan be divided into either soft

23、- or hard-coat types. Soft-coat low-e isfabricated using a sputtering process in a vacuum chamber. This isdone as a post-processing phase after glass has been produced, cut,and stored. The resulting coating is very fragile, especially to theeffects of moisture, so these coatings are normally protect

24、ed insidethe sealed glazing unit. Hard coatings are created using chemicalvapor deposition and are applied to the glass while it is still beingfloated in its final phases of production. This creates a durable low-e coating that can be exposed to moisture and elements.From a performance standpoint, c

25、ategories include (1) high ver-sus low solar gain, (2) spectrally selective, (3) reflective, (4) absorp-tive, and (5) high light-to-solar-gain (LSG) ratio. Some of thesecategories are related and causal. As a rule of thumb, soft coats areoften low solar gain, whereas hard coats are usually high sola

26、r gain.High-solar-gain coatings, which are more transparent to thewhole solar spectrum, are used primarily on south facades in north-ern heating climates in the northern hemisphere (and, conversely, onnorth facades in southern heating climates in the southern hemi-sphere), so solar heat gain during

27、the day can offset thermal heat lossduring long, cold winter nights. When this coating is applied toindoor-facing glazing lites (although still facing the glazing cavity),it further increases the solar heat gain coefficient (SHGC), because ahigher portion of absorbed solar radiation is transferred t

28、o the room(inward-flowing fraction). Their low emissivity helps reduce thermalIR radiation, resulting in increased thermal insulation.Low-solar-gain coatings, which are usually spectrally selectiveblocking admission of the near infrared portion of the solar spec-trum, also known as near IR (NIR) or

29、solar IR, are typically appliedin hot, cooling-dominated regions to reduce solar heat gains, or inbuildings where solar heat gains are not desirable (e.g., commercialbuildings with large fenestration areas or high internal heat gains).Such coatings are normally applied to the outdoor-facing glazingl

30、ite to reduce the inward-flowing fraction of SHGC. The glass sur-faces low emissivity also reduces thermal IR radiation heat transferand therefore increases thermal resistance of the fenestration prod-uct. Although the majority of low-e coatings are applied to the glaz-ing surface facing the glazing

31、 cavity, increasing numbers of durablecoatings are being applied to the room-facing glazing surface. Thisfurther improves thermal performance (U-factor) by substantiallyreducing thermal IR radiation heat transfer on the room side of thewindow. However, in building spaces with higher indoor humidityl

32、evels in cold climates, this approach may significantly increase therisk of moisture condensation on glass surfaces. A new class of low-e surface-applied films may be applied as a retrofit measure to theindoor-facing glass surface; these films can perform similarly tolow-e coated glass, so their use

33、 is more likely to be as an easy retrofitmeasure, removing the need to replace glass or sash.In addition to low-e, fill gases such as argon, krypton, and xenonare used in lieu of air in the gap between glass panes. These fill gasesreduce convective heat transfer across the glazing cavity. Kryptonand

34、 xenon also reduce gap width, because their optimal gap widthsare nearly half that of air.The main requirements of the edge seal are to exclude moisture,provide a desiccant for the sealed space, and retain the glazing unitsstructural integrity. Further, the edge seal isolates the cavitybetween the g

35、lazing materials, thereby reducing the number of sur-faces to be cleaned, and creating an enclosure suitable for nondura-ble low-e coatings and/or fill gases. The edge seal is composed of aspacer, single- or multilevel sealant, and desiccant.The spacer separates glazing layers and provides a surface

36、 forprimary and secondary sealant adhesion. Several types of spacersare used, each of which provides different heat transfer properties,depending on spacer material and geometry.Heat transfer at the edge of the glazing unit is greater than at itscenter because of (1) heat flow through the spacer sys

37、tem and (2)convective flow, which creates an area of higher convective heattransfer as the gas turns from one glazing to the other. To minimizethis heat flow, warm-edge spacers have been developed that reduceedge heat transfer by using materials (e.g., stainless steel, galva-nized steel, tin-plated

38、steel, polymers, foamed silicone) of lowerthermal conductivity than the typical aluminum alloy from whichspacers have often been made. Fusing or bending the corners of thespacer minimizes moisture and hydrocarbon vapor transmissionfrom the gap space.Several different sealant configurations are used

39、in glazing unitconstruction. In dual-seal construction, a primary seal minimizesmoisture transmission and gas escape. A secondary seal providesstructural integrity between the lites of the glazing unit, and ensureslong-term adhesion and greater resistance to solvents, oils, andshort-term water immer

40、sion. In typical dual-seal construction, theprimary seal is made of compressed polyisobutylene (PIB), and thesecondary seal is made of silicone, polysulfide, or polyurethane.Single-seal construction depends on a single sealant to adhere theglazing to the spacer and to minimize moisture transmission

41、and gasescape. Single-seal construction is generally more cost effectivethan dual-seal systems. Dual-seal-equivalent (DSE) materials takeadvantage of advanced cross-linking polymers that provide lowmoisture transmission and structural properties equivalent to dual-seal systems.Desiccants are used to

42、 absorb moisture trapped in the glazingunit during assembly or that gradually diffuses through seals afterconstruction. Typical desiccants include molecular sieve, silica gel,or a matrix of both materials.1.2 FRAMINGThe three main categories of fenestration framing materials arewood, metal, and poly

43、mers. Wood has good structural integrity andinsulating value but low resistance to weather, moisture, warpage,and organic degradation (from mold and insects). Metal is durableand has excellent structural characteristics, but it has very poorFenestration 15.3thermal performance. The metal of choice i

44、n fenestration is almostexclusively aluminum alloy, because of its ease of manufacture,low cost, and low mass, but aluminum alloy has a thermal conduc-tivity roughly 1000 times that of wood or polymers. Steel is some-times used. Although lower in its thermal conductivity, the overallU-factor of a st

45、eel frame is similar to that of an aluminum frame ofthe same geometry. The poor thermal performance of metal-framefenestration can be improved with a thermal break (a nonmetal com-ponent that separates the metal frame exposed to the outdoors fromthe surfaces exposed to the indoors). However, to be m

46、ost effective,there must be thermal breaks in all operable sashes as well as in theframe. Polymer frames are made of extruded vinyl unplasticizedPVC (uPVC) or pultruded fiberglass (glass-reinforced polyester).Their thermal and structural performance is similar to that of wood.Vinyl frames for large

47、fenestration must be reinforced, which de-grades their thermal performance slightly and substantially increasestheir weight. Polymer frames are generally hollow and thus can alsobe filled with polyurethane insulation, which reduces convective andradiative heat transfer, thereby achieving a better th

48、ermal perfor-mance than wood.Manufacturers sometimes combine these materials as clad units(e.g., vinyl-clad aluminum, aluminum-clad wood, vinyl-clad wood)to increase durability, improve thermal performance, or improve aes-thetics. In addition, curtain wall systems for commercial buildingsmay be stru

49、cturally glazed, and the outdoor “framing” is simply rub-ber gaskets or silicone.Generally, the framing system categorizes residential fenestra-tion, as shown by the examples of traditional basic types in Figure2. The glazing system can be mounted either directly in the frame (adirect-glazed or direct-set fenestration, which is not operable) or ina sash that moves in the frame (for an operating fenestration). Inoperable fenestration, a weather-sealing system between the frameand sash reduces air and water leakage.1.3 SHADINGShading devices are available in a wide range of prod