ASHRAE FUNDAMENTALS SI CH 26-2013 Heat Air and Moisture Control In Building Assemblies-Material Properties.pdf

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1、26.1CHAPTER 26HEAT, AIR, AND MOISTURE CONTROL IN BUILDING ASSEMBLIESMATERIAL PROPERTIESINSULATION MATERIALS AND INSULATING SYSTEMS 26.1Apparent Thermal Conductivity. 26.1AIR BARRIERS 26.5WATER VAPOR RETARDERS. 26.6DATA TABLES . 26.7Thermal Property Data 26.7Surface Emissivity and Emittance Data. 26.

2、12Thermal Resistance of Plane Air Spaces . 26.12Air Permeance Data . 26.12Moisture Storage Data . 26.15Soils Data. 26.18SURFACE FILM COEFFICIENTS/RESISTANCES. 26.20Codes and Standards 26.20HIS chapter contains material property data related to theTthermal, air, and moisture performance of building a

3、ssemblies.The information can be used in simplified calculation methods asapplied in Chapter 27, or in software-based methods for transientsolutions. Heat transfer under steady-state and transient conditionsis covered in Chapter 4, and Chapter 25 discusses combined heat/air/moisture transport in bui

4、lding assemblies. For information on ther-mal insulation for mechanical systems, see Chapter 23. For informa-tion on insulation materials used in cryogenic or low-temperatureapplications, see Chapter 47 of the 2010 ASHRAE HandbookRefrigeration. For properties of materials not typically used in build

5、-ing construction, see Chapter 33 of this volume.Density and thermal properties such as thermal conductivity,thermal resistance, specific heat capacity, and emissivity for long-wave radiation are provided for a wide range of building materials,insulating materials, and insulating systems. Air and mo

6、isture prop-erties (e.g., air permeance, water vapor permeance or permeability,capillary water-absorption coefficients, sorption isotherms) aregiven for several materials.Data are also provided on soil thermal conductivity, air cavityresistances, and surface film coefficients, because these are also

7、important factors in performance of building assemblies.INSULATION MATERIALS AND INSULATING SYSTEMSThe main purpose of using thermal insulation materials is toreduce conductive, convective, and radiant heat flows. When prop-erly applied in building envelopes, insulating materials do at leastone of t

8、he following: Increase energy efficiency by reducing the buildings heat loss orgainControl surface temperatures for occupant comfortHelp to control temperatures within an assembly, to reduce thepotential for condensationModulate temperature fluctuations in unconditioned or partly con-ditioned spaces

9、Additional functions may be served, such as providing supportfor a surface finish, impeding water vapor transmission and air leak-age into or out of controlled spaces, reducing damage to structuresfrom exposure to fire and freezing conditions, and providing bettercontrol of noise and vibration. Thes

10、e functions, of course, should beconsistent with the capabilities of the materials.ASTM Standard C168 defines terms related to thermal insulatingmaterials.APPARENT THERMAL CONDUCTIVITYThe primary property of a thermal insulation material is a lowapparent thermal conductivity, though selection of the

11、 appropriatematerial for a given application also involves consideration of theother performance characteristics mentioned previously.Thermal conductivity (symbol k, in Europe) is a property of ahomogeneous, nonporous material. Thermal insulation materials arehighly porous, however, with porosities

12、typically exceeding 90%. Asa consequence, heat transmission involves conduction in the solidmatrix but mainly gas conduction and radiation in the pores (evenconvection can occur in larger pores). This is why the term apparentthermal conductivity is used. That property is affected by structuralparame

13、ters such as density, matrix type (fibrous or cellular), andthickness. Each sample of a given insulation material has a uniquevalue of apparent thermal conductivity for a particular combinationof temperature, temperature difference, moisture content, thickness,and age; that value is not representati

14、ve for other conditions. Formore details, refer to ASTM Standards C168, C177, C335, C518,C1045, and C1363.Influencing ConditionsDensity and Structure. Figure 1 illustrates the variation of theapparent thermal conductivity with density at one mean temperature(i.e., 24C) for a number of insulation mat

15、erials used in buildingenvelopes. For most mass-type insulations, there is a minimum thatnot only depends on the type and form of the material but also ontemperature and direction of heat flow. For fibrous materials, the val-ues of density at which the minimum occurs increase as the fiberdiameter or

16、 cell size; see Figure 2 (Lotz 1969) and mean tempera-ture increase.Structural factors also include compaction and settling of insula-tion, air permeability, type and amount of binder used, additives thatinfluence the bond or contact between fibers or particles, and typeand form of the radiation tra

17、nsfer inhibitor, if any. In cellular mate-rials, most factors that influence strength also control the apparentthermal conductivity: size, shape, and orientation of cells, and thick-ness of cell walls. As Figures 1 and 2 suggest, a specific combinationof cell size, density, and gas composition in th

18、ose materials producesoptimum thermal conductivity.Temperature. At most normal operating temperatures, the appar-ent thermal conductivity of insulating materials generally increaseswith temperature. The rate of change varies with material type anddensity. Some materials, such as fluorocarbon-expande

19、d, closed-cellpolyurethanes, have an inflection in the curve where the fluorocarbonchanges phase from gas to liquid. The apparent thermal conductivityThe preparation of this chapter is assigned to TC 4.4, Building Materialsand Building Envelope Performance.26.2 2013 ASHRAE HandbookFundamentals (SI)o

20、f a sample at one mean temperature (average of the two surface tem-peratures) only applies to the material at the particular thicknesstested. Further testing is required to obtain values suitable for allthicknesses.Insulating materials that allow a large percentage of heat transferby radiation, such

21、 as low-density fibrous and cellular products,show the greatest change in apparent thermal conductivity with tem-perature and surrounding surface emissivity.The effect of temperature on structural integrity is unimportantfor most insulation materials in low-temperature applications. Atvery low tempe

22、ratures, however, some polymeric compounds mayundergo glass transition, which is characterized by a markedincrease in thermal conductivity. For urethanes and butyl-basedcompounds, this occurs at approximately 40C, but for siliconesthe glass transition temperature is more in the range of 90C,which is

23、 not normally encountered in building applications. In anycase, decomposition, excessive linear shrinkage, softening, or othereffects limit the maximum suitable temperature for a material.Moisture Content. The apparent thermal conductivity of insu-lation materials increases with moisture content. If

24、 moisture con-denses in the insulation, it not only reduces thermal resistance, butit may also physically damage the system, because some insulationmaterials deteriorate with exposure to water. Most materials wouldbe damaged if moisture were allowed to freeze in the material,because water expands wh

25、en it freezes. The increase in apparentthermal conductivity depends on the material, temperature, mois-ture content, and moisture distribution. Section A3 of the CIBSEGuide A (CIBSE 2006) covers thermal properties of building struc-tures affected by moisture.Thickness. Radiant heat transfer in pores

26、 of some materialsincreases the measured apparent thermal conductivity. For low-density insulation (e.g., 5.5 kg/m3), the effect becomes more pro-nounced with installed thickness (Pelanne 1979). The effect onthermal resistance is small, even negligible for building applica-tions. No thickness effect

27、 is observed in foam insulation.Age. As mentioned previously, most heat transfer in insulationmaterials at temperatures encountered in buildings and outdoorsoccurs by conduction through air or another gas in the pores (Lander1955; Rowley et al. 1952; Simons 1955; Verschoor and Greebler1952). In fact

28、, heat transfer in dry insulation materials can be closelyapproximated by combining gas conduction with conductionthrough the matrix and radiation in the pores, each determined sep-arately. If air in the pores of a cellular insulation material is replacedby a gas with a different thermal conductivit

29、y, the apparent thermalconductivity changes by an amount approximately equal to the dif-ference between the thermal conductivity of air and the gas. Forexample, replacing air with a fluorinated hydrocarbon (HFC) canlower the apparent thermal conductivity by as much as 50%. Fluo-rocarbon-expanded cel

30、lular plastic foams with a high proportion(i.e., more than 90%) of closed cells retain the fluorocarbon forextended periods of time. Newly produced, they have apparent ther-mal conductivities of approximately 0.022 W/(mK) at 24C. Thisvalue increases with time as air diffuses into the cells and the f

31、luo-rocarbon gas gradually dissolves in the polymer or diffuses out. Dif-fusion rates and increase in apparent thermal conductivity dependon several factors, including permeance of cell walls to the gasesinvolved, foam age, temperature, geometry of the insulation (thick-ness), and integrity of the s

32、urface facing or covering provided. Bran-dreth (1986) and Tye (1988) showed that aging of unfacedpolyurethane and polyisocyanurate is reasonably well understoodanalytically and confirmed experimentally. The dominant parametersfor minimum aging areClosed-cell content 90%, preferably 95%Small, uniform

33、 cell diameter 100 mm 19 to 26 0.039 to 0.040 Four manufacturers (2011)wall application, dense packed 56 0.039 to 0.040 One manufacturer (2011)Perlite, expanded . 32 to 64 0.039 to 0.045 1.1 (Manufacturer, pre 2001)64 to 120 0.045 to 0.052 (Manufacturer, pre 2001)120 to 180 0.052 to 0.061 (Manufactu

34、rer, pre 2001)Glass fiberdattics, 100 to 600 mm . 6.4 to 8.0 0.052 to 0.055 Four manufacturers (2011)attics, 600 to 1100 mm 8 to 9.6 0.049 to 0.052 Four manufacturers (2011)closed attic or wall cavities 29 to 37 0.035 to 0.036 Four manufacturers (2011)Rock and slag wooldattics, 90 to 115 mm 24 to 26

35、 0.049 Three manufacturers (2011)attics, 125 to 430 mm 24 to 29 0.046 to 0.048 Three manufacturers (2011)closed attic or wall cavities 64 0.039 to 0.042 Three manufacturers (2011)Vermiculite, exfoliated 112 to 131 0.068 1.3 Sabine et al. (1975)64 to 96 0.063 Manufacturer (pre 2001)Spray-appliedCellu

36、lose, sprayed into open wall cavities 26 to 42 0.039 to 0.040 Two manufacturers (2011)Glass fiber, sprayed into open wall or attic cavities 16 0.039 to 0.042 Manufacturers association (2011)29 to 37 0.033 to 0.037 Four manufacturers (2011)Polyurethane foam 1.5 Kumaran (2002)low density, open cell 7.

37、2 to 10 0.037 to 0.042 Three manufacturers (2011)medium density, closed cell, aged 180 days 30 to 51 0.020 to 0.029 Five manufacturers (2011)Building Board and SidingBoardAsbestos/cement board 1900 0.57 1.00 Nottage (1947)Cement board. 1150 0.25 0.84 Kumaran (2002)Fiber/cement board 1400 0.25 0.84 K

38、umaran (2002)1000 0.19 0.84 Kumaran (1996)400 0.07 1.88 Kumaran (1996)300 0.06 1.88 Kumaran (1996)Gypsum or plaster board . 640 0.16 1.15 Kumaran (2002)Oriented strand board (OSB).9 to 11 mm 650 0.11 1.88 Kumaran (2002). 12.7 mm 650 0.12 1.88 Kumaran (2002)Plywood (douglas fir) 12.7 mm 460 0.14 1.88

39、 Kumaran (2002). 15.9 mm 540 0.15 1.88 Kumaran (2002)Plywood/wood panels 19.0 mm 450 0.19 1.88 Kumaran (2002)Vegetable fiber board 650 0.11 1.88 Kumaran (2002)sheathing, regular density 12.7 mm 290 0.23 1.30 Lewis (1967)intermediate density. 12.7 mm 350 0.19 1.30 Lewis (1967)nail-based sheathing 12.

40、7 mm 400 0.19 1.30shingle backer9.5 mm 290 0.17 1.30sound deadening board 12.7 mm 240 0.24 1.26tile and lay-in panels, plain or acoustic 290 0.058 0.59laminated paperboard 480 0.072 1.38 Lewis (1967)homogeneous board from repulped paper 480 0.072 1.17Hardboardmedium density . 800 0.105 1.30 Lewis (1

41、967)high density, service-tempered grade and service grade 880 0.12 1.34 Lewis (1967)high density, standard-tempered grade 1010 0.144 1.34 Lewis (1967)Particleboardlow density. 590 0.102 1.30 Lewis (1967)medium density . 800 0.135 1.30 Lewis (1967)high density . 1000 1.18 Lewis (1967)underlayment 15

42、.9 mm 640 1.22 1.21 Lewis (1967)Waferboard 700 0.072 1.88 Kumaran (1996)ShinglesAsbestos/cement 1900 0.037 Wood, 400 mm, 190 mm exposure 0.15 1.30Wood, double, 400 mm, 300 mm exposure. 0.21 1.17Wood, plus ins. backer board. 8 mm 0.25 1.30SidingAsbestos/cement, lapped 6.4 mm 0.037 1.01Asphalt roll si

43、ding . 0.026 1.47Asphalt insulating siding (12.7 mm bed) 0.26 1.47Table 1 Building and Insulating Materials: Design Valuesa(Continued)DescriptionDensity,kg/m3Conductivitybk, W/(mK)Resistance R, (m2K)/WSpecific Heat, kJ/(kgK) ReferencelHeat, Air, and Moisture Control in Building AssembliesMaterial Pr

44、operties 26.9Hardboard siding . 11 mm 0.12 1.17Wood, drop, 200 mm . 25 mm 0.14 1.17Wood, bevel200 mm, lapped 13 mm 0.14 1.17250 mm, lapped 19 mm 0.18 1.17Wood, plywood, lapped 9.5 mm 0.10 1.22Aluminum, steel, or vinyl,h, iover sheathing. hollow-backed . 0.11 1.22iinsulating-board-backed . 9.5 mm 0.3

45、2 1.34foil-backed 9.5 mm 0.52 Architectural (soda-lime float) glass 2500 1.0 0.84Building MembraneVapor-permeable felt . 0.011 Vapor: seal, 2 layers of mopped 0.73 kg/m2felt . 0.21 Vapor: seal, plastic film . Negligible Finish Flooring MaterialsCarpet and rebounded urethane pad 19 mm 110 0.42 NIST (

46、2000)Carpet and rubber pad (one-piece) 9.5 mm 320 0.12 NIST (2000)Pile carpet with rubber pad. 9.5 to 12.7 mm 290 0.28 NIST (2000)Linoleum/cork tile 6.4 mm 465 0.09 NIST (2000)PVC/rubber floor covering 0.40 CIBSE (2006)rubber tile 25 mm 1900 0.06 NIST (2000)terrazzo 25 mm 0.014 0.80Metals (See Chapt

47、er 33, Table 3)RoofingAsbestos/cement shingles 1920 0.037 1.00Asphalt (bitumen with inert fill) . 1600 0.43 CIBSE (2006)1900 0.58 CIBSE (2006)2300 1.15 CIBSE (2006)Asphalt roll roofing . 920 0.027 1.51Asphalt shingles 920 0.078 1.26Built-up roofing . 10 mm 920 0.059 1.47Mastic asphalt (heavy, 20% gr

48、it) 950 0.19 CIBSE (2006)Reed thatch 270 0.09 CIBSE (2006)Roofing felt 2250 1.20 CIBSE (2006)Slate . 13 mm 0.009 1.26Straw thatch . 240 0.07 CIBSE (2006)Wood shingles, plain and plastic-film-faced . 0.166 1.30Plastering MaterialsCement plaster, sand aggregate . 1860 0.72 0.84Sand aggregate. 10 mm 0.013 0.84. 20 mm 0.026 0.84Gypsum plaster 1120 0.38 CIBSE (2006)1280 0.46 CIBSE (2006)Lightweight aggregate . 13 mm 720 0.056 16 mm 720 0.066 on metal lath 19 mm 0.083 Perlite aggregate 720 0.22 1.34Sand aggregate. 1680 0.81 0.84on metal lath 19 m