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., 75F) 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 HandbookFundamentalsof a s
20、ample 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 as l
21、ow-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 temperatur
22、es, 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 40F, but for siliconesthe glass transition temperature is more in the range of 130F,which is not
23、 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 moi
24、sture 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 when i
25、t 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 of
26、some materialsincreases the measured apparent thermal conductivity. For low-density insulation (e.g., 0.35 lb/ft3), 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 i
27、s 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 conductivity,
29、 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 cellu
30、lar 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 0.15 Btuin/hft2F at 75F.This value increases with time as air diffuses into the cells and the
31、fluorocarbon gas gradually dissolves in the polymer or diffuses out.Diffusion rates and increase in apparent thermal conductivitydepend on several factors, including permeance of cell walls to thegases involved, foam age, temperature, geometry of the insulation(thickness), and integrity of the surfa
32、ce facing or covering provided.Brandreth (1986) and Tye (1988) showed that aging of unfaced poly-urethane and polyisocyanurate is reasonably well understood analyt-ically and confirmed experimentally. The dominant parameters forminimum aging areClosed-cell content 90%, preferably 95%Small, uniform c
33、ell diameter 4 in. . 1.2 to 1.6 0.27 to 0.28 Four manufacturers (2011)wall application, densely packed . 3.5 0.27 0.28 One manufacturer (2011) Perlite, expanded 2 to 4 0.27 to 0.31 0.26 (Manufacturer, pre-2001)4 to 7.5 0.31 to 0.36 (Manufacturer, pre-2001)7.5 to 11 0.36 to 0.42 (Manufacturer, pre-20
34、01)Glass fiberdattics, 4 to 12 in 0.4 to 0.5 0.36 to 0.38 Four manufacturers (2011)attics, 12 to 22 in 0.5 to 0.6 0.34 to 0.36 Four manufacturers (2011)closed attic or wall cavities 1.8 to 2.3 0.24 to 0.25 Four manufacturers (2011)Rock and slag wooldattics, 3.5 to 4.5 in 1.5 to 1.6 0.34 Three manufa
35、cturers (2011)attics, 5 to 17 in 1.5 to 1.8 0.32 to 0.33 Three manufacturers (2011)closed attic or wall cavities . 4.0 0.27 to 0.29 Three manufacturers (2011)Vermiculite, exfoliated 7.0 to 8.2 0.47 0.32 Sabine et al. (1975)4.0 to 6.0 0.44 Manufacturer (pre-2001)Spray appliedCellulose, sprayed into o
36、pen wall cavities 1.6 to 2.6 0.27 to 0.28 Two manufacturers (2011)Glass fiber, sprayed into open wall or attic cavities 1.0 0.27 to 0.29 Manufacturers association (2011)1.8 to 2.3 0.23 to 0.26 Four manufacturers (2011)Polyurethane foam 0.35 Kumaran (2002)low density, open cell . 0.45 to 0.65 0.26 to
37、 0.29 Three manufacturers (2011)medium density, closed cell, aged 180 days . 1.9 to 3.2 0.14 to 0.20 Five manufacturers (2011)Building Board and SidingBoardAsbestos/cement board 120 4 0.24 Nottage (1947)Cement board. 71 1.7 0.2 Kumaran (2002)Fiber/cement board 88 1.7 0.2 Kumaran (2002)61 1.3 0.2 Kum
38、aran (1996)26 0.5 0.45 Kumaran (1996)20 0.4 0.45 Kumaran (1996)Gypsum or plaster board 40 1.1 0.21 Kumaran (2002)Oriented strand board (OSB) 7/16 in. 41 0.62 0.45 Kumaran (2002)1/2 in. 41 0.68 0.45 Kumaran (2002)Plywood (douglas fir) . 1/2 in. 29 0.79 0.45 Kumaran (2002)5/8 in. 34 0.85 0.45 Kumaran
39、(2002)Plywood/wood panels . 3/4 in. 28 1.08 0.45 Kumaran (2002)Vegetable fiber boardsheathing, regular density . 1/2 in. 18 1.32 0.31 Lewis (1967)intermediate density 1/2 in. 22 1.09 0.31 Lewis (1967)nail-based sheathing 1/2 in. 25 1.06 0.31shingle backer . 3/8 in. 18 0.94 0.3sound-deadening board 1
40、/2 in. 15 1.35 0.3tile and lay-in panels, plain or acoustic 18 0.4 0.14laminated paperboard. 30 0.5 0.33 Lewis (1967)homogeneous board from repulped paper . 30 0.5 0.28Hardboardmedium density 50 0.73 0.31 Lewis (1967)high density, service-tempered and service grades 55 0.82 0.32 Lewis (1967)high den
41、sity, standard-tempered grade 63 1.0 0.32 Lewis (1967)Particleboardlow density. 37 0.71 0.31 Lewis (1967)medium density 50 0.94 0.31 Lewis (1967)high density 62 1.18 0.85 Lewis (1967)underlayment 5/8 in. 44 0.73 0.82 0.29 Lewis (1967)Waferboard. 37 0.63 0.21 0.45 Kumaran (1996)ShinglesAsbestos/cemen
42、t 120 0.21 Wood, 16 in., 7 1/2 in. exposure 0.87 0.31Wood, double, 16 in., 12 in. exposure . 1.19 0.28Wood, plus ins. backer board 5/16 in. 1.4 0.31SidingAsbestos/cement, lapped. 1/4 in. 0.21 0.24Asphalt roll siding 0.15 0.35Asphalt insulating siding (1/2 in. bed). 0.21 0.24Table 1 Building and Insu
43、lating Materials: Design Valuesa(Continued)DescriptionDensity,lb/ft3Conductivitybk, Btuin/hft2FResistance R, hft2F/BtuSpecific Heat, Btu/lbF ReferencelHeat, Air, and Moisture Control in Building AssembliesMaterial Properties 26.9Hardboard siding. 7/16 in. 0.15 0.35Wood, drop, 8 in. 1 in. 0.79 0.28Wo
44、od, bevel8 in., lapped1/2 in. 0.81 0.2810 in., lapped3/4 in. 1.05 0.28Wood, plywood, 3/8 in., lapped . 0.59 0.29Aluminum, steel, or vinyl,h, iover sheathing . hollow-backed 0.62 0.29iinsulating-board-backed 3/8 in. 1.82 0.32foil-backed 3/8 in. 2.96 Architectural (soda-lime float) glass 158 6.9 0.21B
45、uilding MembraneVapor-permeable felt 0.06 Vapor: seal, 2 layers of mopped 15 lb felt . 0.12 Vapor: seal, plastic film Negligible Finish Flooring MaterialsCarpet and rebounded urethane pad 3/4 in. 7 2.38 NIST (2000)Carpet and rubber pad (one-piece) 3/8 in. 20 0.68 NIST (2000)Pile carpet with rubber p
46、ad 3/8 to 1/2 in. 18 1.59 NIST (2000)Linoleum/cork tile. 1/4 in. 29 0.51 NIST (2000)PVC/rubber floor covering 2.8 CIBSE (2006)rubber tile 1.0 in. 119 0.34 NIST (2000)terrazzo 1.0 in. 0.08 0.19Metals (See Chapter 33, Table 3)RoofingAsbestos/cement shingles 120 0.21 0.24Asphalt (bitumen with inert fil
47、l) 100 2.98 CIBSE (2006)119 4.0 CIBSE (2006)144 7.97 CIBSE (2006)Asphalt roll roofing 70 0.15 0.36Asphalt shingles. 70 0.44 0.3Built-up roofing 3/8 in. 70 0.33 0.35Mastic asphalt (heavy, 20% grit) . 59 1.32 CIBSE (2006)Reed thatch 17 0.62 CIBSE (2006)Roofing felt 141 8.32 CIBSE (2006)Slate 1/2 in. 0
48、.05 0.3Straw thatch . 15 0.49 CIBSE (2006)Wood shingles, plain and plastic-film-faced 0.94 0.31 Plastering MaterialsCement plaster, sand aggregate 116 5.0 0.2Sand aggregate 3/8 in. 0.08 0.23/4 in. 0.15 0.2Gypsum plaster 70 2.63 CIBSE (2006)80 3.19 CIBSE (2006)Lightweight aggregate 1/2 in. 45 0.32 5/8 in. 45 0.39 on metal lath 3/4 in. 0.47 Perlite aggregate. 45 1.5 0.32Sand aggregate. 105 5.6 0.2on metal lath 3/4 in. 0.13 Vermiculite aggregate 30 1.0 CIBSE (2006)40 1.39 CIBSE (2006)45 1.7 CIBSE (2006)50 1.8 CIBSE (2006)60 2.08
