21.1 CHAPTER 21 PHYSICAL PROPERTIES OF SECONDARY COOLANTS (BRINES) Brines 21.1 Inhibited Glycols 21.4 Halocarbons 21.12 Nonhalocarbon, Nonaqueous Fluids 21.12 N MANY refrigeration applications, heat is transferred to a sec- Iondary coolant, which can be any liquid cooled by the refriger- ant and used to transfer heat without changing state. These liquids are also known as heat transfer fluids, brines, or secondary refrigerants. Other ASHRAE Handbooks describe various applications for secondary coolants. In the 1998 ASHRAE Handbook—Refrigera- tion, refrigeration systems are discussed in Chapter 4, their uses in food processing are found in Chapters 14 through 28, and ice rinks are discussed in Chapter 34. In the 1999 ASHRAE Handbook— Applications, solar energy use is discussed in Chapter 32, thermal storage in Chapter 33, and snow melting in Chapter 49. This chapter describes the physical properties of several second- ary coolants and provides information on their use. The chapter also includes information on corrosion protection. Additional informa- tion on corrosion inhibition can be found in Chapter 47 of the 1999 ASHRAE Handbook—Applications and Chapter 4 of the 1998 ASHRAE Handbook—Refrigeration. BRINES Physical Properties Water solutions of calcium chloride and sodium chloride are the most common refrigeration brines. Tables 1 and 2 list the properties of pure calcium chloride brine and sodium chloride brine. For com- mercial grades, use the formulas in the footnotes to these tables. Fig- ures 1 and 5 give the specific heats for calcium chloride and sodium chloride brines and are used for computation of heat loads with ordi- nary brine (Carrier 1959). Figures 2 and 6 show the ratio of the mass of the solution to that of water, which is commonly used as the mea- sure of salt concentration. Viscosities are given in Figures 3 and 7. Figures 4 and 8 show thermal conductivity of calcium and sodium brines at varying temperatures and concentrations. Brine applications in refrigeration are mainly in the industrial machinery field and in skating rinks. Corrosion is the principal problem for calcium chloride brines, especially in ice-making tanks where galvanized iron cans are immersed. The preparation of this chapter is assigned to TC 3.1, Refrigerants and Brines. Fig. 1 Specific Heat of Calcium Chloride Brines Fig. 2 Density of Calcium Chloride Brines Physical Properties of Secondary Coolants (Brines) 21.5 amorphous, undercooled liquid of extremely high viscosities that has all the appearances of a solid). On the dilute side of the eutectic, ice forms on freezing; on the concentrated side, solid glycol separates from solution on freezing. The freezing velocity of such solutions is often quite slow; but, in time, they set to a hard, solid mass. Physical properties (i.e., density, specific heat, thermal conduc- tivity, and viscosity) for aqueous solutions of ethylene glycol can be found in Tables 6 through 9 and Figures 9 through 12; similar data for aqueous solutions of propylene glycol can be found in Tables 10 through 13 and Figures 13 through 16. Densities are for aqueous solutions of industrially inhibited glycols. These densities are somewhat higher than those for pure glycol and water alone. Typical corrosion inhibitor packages do not significantly affect the other physical properties. The physical properties for the two fluids are similar, with the exception of viscosity. At the same concen- tration, aqueous solutions of propylene glycol are more viscous than solutions of ethylene glycol. This higher viscosity accounts for the majority of the performance difference between the two fluids. The choice of glycol concentration depends on the type of protec- tion required by the application. If the fluid is being used to prevent equipment damage during idle periods in cold weather, such as win- terizing coils in an HVAC system, 30% ethylene glycol or 35% pro- pylene glycol is sufficient. These concentrations will allow the fluid to freeze. As the fluid freezes, it forms a slush that expands and flows into any available space. Therefore, expansion volume must be included with this type of protection. If the application requires that the fluid remain entirely liquid, a concentration with a freezing point 3°C below the lowest expected temperature should be chosen. Avoid excessive glycol concentration because it increases initial cost and adversely affects the physical properties of the fluid. Table 4 Freezing and Boiling Points of Aqueous Solutions of Ethylene Glycol Percent Ethylene Glycol Freezing Point, °C Boiling Point, °C at 100.7 kPaBy Mass By Volume 0.0 0.0 0.0 100.0 5.0 4.4 −1.4 100.6 10.0 8.9 −3.2 101.1 15.0 13.6 −5.4 101.7 20.0 18.1 −7.8 102.2 21.0 19.2 −8.4 102.2 22.0 20.1 −8.9 102.2 23.0 21.0 −9.5 102.8 24.0 22.0 −10.2 102.8 25.0 22.9 −10.7 103.3 26.0 23.9 −11.4 103.3 27.0 24.8 −12.0 103.3 28.0 25.8 −12.7 103.9 29.0 26.7 −13.3 103.9 30.0 27.7 −14.1 104.4 31.0 28.7 −14.8 104.4 32.0 29.6 −15.4 104.4 33.0 30.6 −16.2 104.4 34.0 31.6 −17.0 104.4 35.0 32.6 −17.9 105.0 36.0 33.5 −18.6 105.0 37.0 34.5 −19.4 105.0 38.0 35.5 −20.3 105.0 39.0 36.5 −21.3 105.0 40.0 37.5 −22.3 105.6 41.0 38.5 −23.2 105.6 42.0 39.5 −24.3 105.6 43.0 40.5 −25.3 106.1 44.0 41.5 −26.4 106.1 45.0 42.5 −27.5 106.7 46.0 43.5 −28.8 106.7 47.0 44.5 −29.8 106.7 48.0 45.5 −31.1 106.7 49.0 46.6 −32.6 106.7 50.0 47.6 −33.8 107.2 51.0 48.6 −35.1 107.2 52.0 49.6 −36.4 107.2 53.0 50.6 −37.9 107.8 54.0 51.6 −39.3 107.8 55.0 52.7 −41.1 108.3 56.0 53.7 −42.6 108.3 57.0 54.7 −44.2 108.9 58.0 55.7 −45.6 108.9 59.0 56.8 −47.1 109.4 60.0 57.8 −48.3 110.0 65.0 62.8 a 112.8 70.0 68.3 a 116.7 75.0 73.6 a 120.0 80.0 78.9 −46.8 123.9 85.0 84.3 −36.9 133.9 90.0 89.7 −29.8 140.6 95.0 95.0 −19.4 158.3 a Freezing points are below −50°C. Table 5 Freezing and Boiling Points of Aqueous Solutions of Propylene Glycol Percent Propylene Glycol Freezing Point, °C Boiling Point, °C at 100.7 kPaBy Mass By Volume 0.0 0.0 0.0 100.0 5.0 4.8 −1.6 100.0 10.0 9.6 −3.3 100.0 15.0 14.5 −5.1 100.0 20.0 19.4 −7.1 100.6 21.0 20.4 −7.6 100.6 22.0 21.4 −8.0 100.6 23.0 22.4 −8.6 100.6 24.0 23.4 −9.1 100.6 25.0 24.4 −9.6 101.1 26.0 25.3 −10.2 101.1 27.0 26.4 −10.8 101.1 28.0 27.4 −11.4 101.7 29.0 28.4 −12.0 101.7 30.0 29.4 −12.7 102.2 31.0 30.4 −13.4 102.2 32.0 31.4 −14.1 102.2 33.0 32.4 −14.8 102.2 34.0 33.5 −15.6 102.2 35.0 34.4 −16.4 102.8 36.0 35.5 −17.3 102.8 37.0 36.5 −18.2 102.8 38.0 37.5 −19.1 103.3 39.0 38.5 −20.1 103.3 40.0 39.6 −21.1 103.9 41.0 40.6 −22.1 103.9 42.0 41.6 −23.2 103.9 43.0 42.6 −24.3 103.9 44.0 43.7 −25.5 103.9 45.0 44.7 −26.7 104.4 46.0 45.7 −27.9 104.4 47.0 46.8 −29.3 104.4 48.0 47.8 −30.6 105.0 49.0 48.9 −32.1 105.0 50.0 49.9 −33.5 105.6 51.0 50.9 −35.0 105.6 52.0 51.9 −36.6 105.6 53.0 53.0 −38.2 106.1 54.0 54.0 −39.8 106.1 55.0 55.0 −41.6 106.1 56.0 56.0 −43.3 106.1 57.0 57.0 −45.2 106.7 58.0 58.0 −47.1 106.7 59.0 59.0 −49.0 106.7 60.0 60.0 −51.1 107.2 65.0 65.0 a 108.3 70.0 70.0 a 110.0 75.0 75.0 a 113.9 80.0 80.0 a 118.3 85.0 85.0 a 125.0 90.0 90.0 a 132.2 95.0 95.0 a 154.4 a Above 60% by mass, solutions do not freeze but become a glass. Physical Properties of Secondary Coolants (Brines) 21.13 cost and relative novelty. Before choosing these types of fluids, con- sider electrical classifications, disposal, potential worker exposure, process containment, and other relevant issues. Tables 17 through 19 contain physical property information on a mixture of dimethylsiloxane polymers of various relative molecu- lar masses (Dow Corning 1989) and d-limonene. Information on d-limonene is limited; it is based on measurements made over small data temperature ranges or simply on standard physical property estimation techniques. The compound is an optically active terpene (molecular formula C 10 H 16 ) derived as an extract from orange and lemon oils. The “d” indicates that the material is dextrorotatory, which is a physical property of the material that does not affect the transport properties of the material significantly. The mixture of dimethylsiloxane polymers can be used with most standard construction materials; d-limonene, however, can be quite corrosive, easily autooxidizing at ambient temperatures. This fact should be understood and considered before using d-limonene in a system. REFERENCES ACGIH. 1998. Threshold limit values and biological exposure indices. Pub- lished annually by the American Conference of Governmental Industrial Hygienists, Cincinnati, OH. Carrier Air Conditioning Company. 1959. Basic data, Section 17M. Syra- cuse, NY. Dow Corning USA. 1989. Syltherm heat transfer liquids. Midland, MI. BIBLIOGRAPHY Born, D.W. 1989. Inhibited glycols for corrosion and freeze protection in water-based heating and cooling systems. Midland, MI. CCI. Calcium chloride for refrigeration brine. Manual RM-1. Calcium Chlo- ride Institute. Dow Chemical USA. 1994. Engineering manual for DOWFROST and DOWFROST HD heat transfer fluids. Midland, MI. Dow Chemical USA. 1996. Engineering manual for Dowtherm SR-1 and Dowtherm 4000 heat transfer fluids. Midland, MI. Fontana, M.G. 1986. Corrosion engineering. McGraw-Hill, New York. NACE. 1973. Corrosion inhibitors. National Association of Corrosion Engineers, Houston, TX. NACE. 1991. NACE corrosion engineer’s reference book. NACE. 2000. Corrosion: Understanding the basics. Union Carbide Corporation. 1994. Ucartherm heat transfer fluids. South Charleston, WV. Table 18 Properties of a Polydimethylsiloxane Heat Transfer Fluid Temper- ature, °C Vapor Pressure, kPa Viscosity, mPa· s Density, kg/m 3 Heat Capacity, kJ/(kg·K) Thermal Conductivity, W/(m·K) −73 0.00 12.4 924.6 1.410 0.1294 −70 0.00 11.2 922.1 1.418 0.1288 −60 0.00 8.26 913.5 1.443 0.1269 −50 0.00 6.24 905.0 1.469 0.1251 −40 0.00 4.83 896.4 1.495 0.1231 −30 0.00 3.81 887.9 1.520 0.1212 −20 0.00 3.07 879.3 1.546 0.1192 −10 0.01 2.51 870.7 1.572 0.1171 0 0.03 2.09 862.0 1.597 0.1150 10 0.08 1.76 853.3 1.623 0.1129 20 0.16 1.49 844.5 1.649 0.1108 30 0.32 1.29 835.5 1.674 0.1086 40 0.61 1.12 826.5 1.700 0.1064 50 1.09 0.98 817.3 1.726 0.1042 60 1.85 0.86 807.9 1.751 0.1019 70 3.02 0.77 798.4 1.777 0.0996 80 4.76 0.69 788.7 1.803 0.0973 90 7.25 0.62 778.8 1.828 0.0949 100 10.73 0.56 768.7 1.854 0.0925 110 15.45 0.51 758.3 1.880 0.0901 120 21.75 0.47 747.7 1.905 0.0877 130 29.95 0.43 736.8 1.931 0.0852 140 40.45 0.40 725.6 1.957 0.0827 150 53.67 0.37 714.1 1.982 0.0802 160 70.06 0.34 702.3 2.008 0.0777 170 90.10 0.32 690.2 2.033 0.0751 180 114.29 0.30 677.7 2.059 0.0725 190 143.17 0.28 664.8 2.085 0.0699 200 177.27 0.26 651.6 2.110 0.0673 210 217.14 0.25 638.0 2.136 0.0646 220 263.36 0.24 623.9 2.162 0.0620 230 316.47 0.22 609.5 2.187 0.0593 240 377.03 0.21 594.5 2.213 0.0566 250 445.61 0.20 579.1 2.239 0.0538 260 522.74 0.19 563.3 2.264 0.0511 Table 19 Physical Properties of d-Limonene Temper- ature, °C Specific Heat, kJ/(kg ·K) Viscosity, mPa· s Density, kg/m 3 Thermal Conductivity, W/(m·K) −73 1.27 3.8 914.3 0.137 −50 1.39 3 897.1 0.133 −25 1.51 2.3 878.3 0.128 0 1.65 1.8 859.2 0.124 25 1.78 1.4 839.8 0.119 50 1.91 1.1 820.1 0.114 75 2.04 0.8 800 0.11 100 2.17 0.7 779.5 0.105 125 2.3 0.5 758.4 0.1 150 2.41 0.4 736.6 0.096 Note: Properties are estimated or based on incomplete data. 22.1 CHAPTER 22 SORBENTS AND DESICCANTS Desiccant Applications 22.1 Desiccant Cycle 22.1 Types of Desiccants 22.3 Desiccant Isotherms 22.5 Desiccant Life 22.5 Cosorption of Water Vapor and Indoor Air Contaminants 22.6 ORPTION refers to the binding of one substance to another. SSorbents are materials that have an ability to attract and hold other gases or liquids. They can be used to attract gases or liquids other than water vapor, a characteristic that makes them very useful in chemical separation processes. Desiccants are a subset of sor- bents; they have a particular affinity for water. Virtually all materials are desiccants; that is, they attract and hold water vapor. Wood, natural fibers, clays, and many synthetic mate- rials attract and release moisture as commercial desiccants do, but they lack the holding capacity. For example, woolen carpet fibers attract up to 23% of their dry mass in water vapor, and nylon can take up almost 6% of its mass in water. In contrast, a commercial desiccant takes up between 10 and 1100% of its dry mass in water vapor, depending on its type and on the moisture available in the environment. Furthermore, commercial desiccants continue to attract moisture even when the surrounding air is quite dry, a char- acteristic that other materials do not share. All desiccants behave in a similar way—they attract moisture until they reach equilibrium with the surrounding air. Moisture is usually removed from the desiccant by heating it to temperatures between 50 and 260°C and exposing it to a scavenger airstream. After the desiccant dries, it must be cooled so that it can attract moisture once again. Sorption always generates sensible heat equal to the latent heat of the water vapor taken up by the desiccant plus an additional heat of sorption that varies between 5 and 25% of the latent heat of the water vapor. This heat is transferred to the desic- cant and to the surrounding air. The process of attracting and holding moisture is described as either adsorption or absorption, depending on whether the desiccant undergoes a chemical change as it takes on moisture. Adsorption does not change the desiccant, except by the addition of the mass of water vapor; it is similar in some ways to a sponge soaking up water. Absorption, on the other hand, changes the desiccant. An example of an absorbent is table salt, which changes from a solid to a liquid as it absorbs moisture. DESICCANT APPLICATIONS Desiccants can dry either liquids or gases, including ambient air, and are used in many air-conditioning applications, particularly when • The latent load is large in comparison to the sensible load. • The cost of energy to regenerate the desiccant is low compared to the cost of energy to dehumidify the air by chilling it below its dew point. • The moisture control level for the space would require chilling the air to subfreezing dew points if compression refrigeration alone were used to dehumidify the air. • The temperature control level for the space or process requires continuous delivery of air at subfreezing temperatures. In any of these situations, the cost of running a vapor compres- sion cooling system can be very high. A desiccant process may offer considerable advantages in energy, initial cost of equipment, and maintenance. Because desiccants are able to attract and hold more than simply water vapor, they can remove contaminants from airstreams to improve indoor air quality. Desiccants have been used to remove organic vapors and, in special circumstances, to control microbio- logical contaminants (Batelle 1971, Buffalo Testing Laboratory 1974). Hines et al. (1991) have also confirmed the usefulness of desiccants in removing vapors that can degrade indoor air quality. Desiccant materials are capable of adsorbing hydrocarbon vapors while they are collecting moisture from air. These desiccant cosorp- tion phenomena show promise of improving indoor air quality in typical building HVAC systems. Desiccants are also used in drying compressed air to low dew points. In this application, moisture can be removed from the desic- cant without heat. Desorption is accomplished using differences in vapor pressures compared to the total pressures of the compressed and ambient pressure airstreams. Finally, desiccants are used to dry the refrigerant circulating in air-conditioning and refrigeration systems. This reduces corrosion in refrigerant piping and prevents valves and capillaries from becoming clogged with ice crystals. In this application, the desic- cant is not regenerated; it is discarded when it has adsorbed its limit of water vapor. This chapter discusses the water sorption characteristics of des- iccant materials and explains some of the implications of those char- acteristics in ambient pressure air-conditioning applications. Information on other applications for desiccants can be found in Chapters 14 and 29 of this volume, Chapters 6, 25, 34, 41, and 46 of the 1998 ASHRAE Handbook—Refrigeration, Chapters 1, 2, 5, 8, 15, 17, 20, 27, and 44 of the 1999 ASHRAE Handbook—Applica- tions, and Chapters 22 and 44 of the 2000 ASHRAE Handbook— Systems and Equipment. DESICCANT CYCLE Practically speaking, all desiccants function by the same mech- anism—transferring moisture because of a difference between the water vapor pressure at their surface and that of the surrounding air. When the vapor pressure at the desiccant surface is lower than that of the air, the desiccant attracts moisture. When the surface vapor pressure is higher than that of the surrounding air, the desiccant releases moisture. Figure 1 shows the relationship between the moisture content of the desiccant and its surface vapor pressure. As the moisture content of the desiccant rises, so does the water vapor pressure at its surface. At some point, the vapor pressure at the desiccant surface is the The preparation of this chapter is assigned to TC 3.5, Desiccant and Sorp- tion Technology. 22.4 2001 ASHRAE Fundamentals Handbook (SI) As a practical matter, however, the absorption process is limited by the exposed surface area of the desiccant and by the contact time allowed for the reaction. More surface area and more contact time allow the desiccant to approach its theoretical capacity. Commercial desiccant systems stretch these limits by flowing the liquid desic- cant onto an extended surface much like in a cooling tower. Solid Adsorbents Adsorbents are solid materials with a tremendous internal surface area per unit of mass; a single gram can have more than 4600 m 2 of surface area. Structurally, adsorbents resemble a rigid sponge, and the surface of the sponge in turn resembles the ocean coastline of a fjord. This analogy indicates the scale of the differ- ent surfaces in an adsorbent. The fjords can be compared to the capillaries in the adsorbent. The spaces between the grains of sand on the fjord beaches can be compared to the spaces between the individual molecules of the adsorbent, all of which have the capacity to hold water molecules. The bulk of the adsorbed water is contained by condensation into the capillaries, and the majority of the surface area that attracts individual water molecules is in the crystalline structure of the material itself. Adsorbents attract moisture because of the electrical field at the desiccant surface. The field is not uniform in either force or charge, so specific sites on the desiccant surface attract water molecules that have a net opposite charge. When the complete surface is covered, the adsorbent can hold still more moisture because vapor condenses into the first water layer and fills the capillaries throughout the material. As with liquid absorbents, the ability of an adsorbent to attract moisture depends on the difference in vapor pressure between its surface and the air. The capacity of solid adsorbents is generally less than the capac- ity of liquid absorbents. For example, a typical molecular sieve adsorbent can hold 17% of its dry mass in water when the air is at 21°C and 20% rh. In contrast, LiCl can hold 130% of its mass at the same temperature and relative humidity. But solid adsorbents have several other favorable characteristics. For example, molecular sieves continue to adsorb moisture even when they are quite hot, allowing dehumidification of very warm airstreams. Also, several solid adsorbents can be manufactured to precise tolerances, with pore diameters that can be closely con- trolled. This means they can be tailored to adsorb molecules of a specific diameter. Water, for example, has an effective molecular diameter of 3.2 nm. A molecular sieve adsorbent with an average pore diameter of 4.0 nm adsorbs water but has almost no capacity for larger molecules, such as organic solvents. This selective adsorption characteristic is useful in many applications. For exam- ple, several desiccants with different pore sizes can be combined in series to remove first water and then other specific contaminants from an airstream. Adsorption Behavior. The adsorption behavior of solid adsor- bents depends on (1) total surface area, (2) total volume of capillar- ies, and (3) range of capillary diameters. A large surface area gives the adsorbent a larger capacity at low relative humidities. Large cap- illaries provide a high capacity for condensed water, which gives the adsorbent a higher capacity at high relative humidities. A narrow range of capillary diameters makes an adsorbent more selective in the vapor molecules it can hold. In designing a desiccant, some trade-offs are necessary. For example, materials with large capillaries necessarily have a smaller surface area per unit of volume than those with smaller capillaries. As a result, adsorbents are sometimes combined to provide a high adsorption capacity across a wide range of operating conditions. Figure 6 illustrates this point using three noncommercial silica gel adsorbents prepared for use in laboratory research. Each has a dif- ferent internal structure, but since they are all silicas, they have sim- ilar surface adsorption characteristics. Gel 1 has large capillaries, making its total volume large but its total surface area small. It has a large adsorption capacity at high relative humidities but adsorbs a small amount at low relative humidities. In contrast, Gel 8 has a capillary volume one-seventh the size of Gel 1, but a total surface area almost twice as large. This gives it a higher capacity at low relative humidities but a lower capacity to hold the moisture that condenses at high relative humidities. Silica gels and most other adsorbents can be manufactured to provide optimum performance in a specific application, balancing capacity against strength, mass, and other favorable characteristics (Bry-Air 1986). Types of Solid Adsorbents. General classes of solid adsorbents include • Silica gels • Zeolites • Synthetic zeolites (molecular sieves) • Activated aluminas • Carbons • Synthetic polymers Silica gels are amorphous solid structures formed by condens- ing soluble silicates from solutions of water or other solvents. They have the advantages of relatively low cost and relative sim- plicity of structural customizing. They are available as large as spherical beads about 5 mm in diameter or as small as grains of a fine powder. Gel Number Total Surface Area, m 2 /g Average Capillary Diameter, nm Total Volume of Capillaries, mm 3 /g 1 315 21 1700 5 575 3.8 490 8 540 2.2 250 Fig. 6 Adsorption and Structural Characteristics of Some Experimental Silica Gels (Oscic and Cooper 1982) 23.1 CHAPTER 23 THERMAL AND MOISTURE CONTROL IN INSULATED ASSEMBLIES—FUNDAMENTALS Terminology and Symbols 23.1 THERMAL INSULATION 23.2 Basic Materials 23.2 Physical Structure and Form 23.2 Properties 23.2 HEAT FLOW 23.4 Factors Affecting Thermal Performance 23.4 Thermal Transmittance 23.6 Factors Affecting Heat Transfer Across Air Spaces 23.7 Calculating Overall Thermal Resistance 23.8 Calculating Interface Temperatures 23.8 Heat Flow Calculations 23.8 INSULATION THICKNESS 23.9 Economic Thickness 23.9 Economic Thickness: Mechanical Systems 23.9 Economic Thickness: Building Envelopes 23.10 MOISTURE IN BUILDINGS 23.11 Moisture Problems in Buildings 23.11 Properties of Water Vapor in Air 23.13 Moisture in Building Materials 23.13 Moisture Migration 23.14 Water Vapor Retarders and Airflow Retarders 23.15 Steady-State Design Tools 23.17 Mathematical Models 23.19 Preventing Surface Condensation 23.20 ROPER DESIGN of space heating, air-conditioning, refrig- Peration, and other industrial systems requires knowledge of thermal insulations and thermal-moisture behavior of building structures. This chapter deals with heat and moisture transfer defi- nitions, fundamentals and properties of thermal insulation materi- als, heat flow calculations, economic thickness of insulation, and the fundamentals of moisture as it relates to building components and systems. TERMINOLOGY AND SYMBOLS The following heat and moisture transfer definitions and sym- bols are commonly used in the building industry. Thermal transmission, heat transfer, or rate of heat flow. The flow of heat energy induced by a temperature difference. Heat may be transferred by conduction, convection, radiation, and mass trans- fer. These can occur separately or in combinations, depending on specific circumstances. Thermal conductivity, k. The time rate of heat flow through a unit area of 1 m thick homogeneous material in a direction perpendicular to isothermal planes, induced by a unit temperature gradient. (ASTM Standard C 168 defines homogeneity.) Units are W/(m·K). Thermal conductivity must be evaluated for a specific mean temperature and moisture content, because in most materials it varies with temperature and moisture content. For porous materials, heat flows by a combination of modes and may depend on orientation, direction, or both. The measured prop- erty of such materials may be called effective or apparent thermal conductivity. The specific test conditions (i.e., sample thickness, orientation, environment, environmental pressure, surface temper- ature, mean temperature, temperature difference, and moisture con- tent) should be reported with the values. With thermal conductivity, the symbol k app is used to denote the lack of pure conduction or to indicate that all values reported are apparent. Thermal resistivity, R u . The reciprocal of thermal conductivity. Units are m·K/W. Thermal conductance, C-factor, C. Thetimerateofheatflow through a unit area of a body induced by a unit temperature differ- ence between the body surfaces. Units are W/(m 2 ·K). When the two defined surfaces of mass-type (i.e., nonreflec- tive) thermal insulation have unequal areas, as in the case of radial heat flow through a curved block or through a pipe cover- ing (see Table 2 in Chapter 3), or through materials of nonuni- form thickness, an appropriate mean area and mean thickness must be given. Heat flow formulas involving materials that are not uniform slabs must contain shape factors to account for the area variation involved. When heat flow occurs by conduction alone, the thermal con- ductance of a material may be obtained by dividing the thermal conductivity of the material by its thickness. When several modes of heat transfer are involved, the apparent or effective thermal conductance may be obtained by dividing the apparent thermal conductivity by the thickness. Where air circulates within or passes through insulation, as it may with low-density fibrous materials, the effective thermal con- ductance is affected. Thermal conductances and resistances of the more common building materials and industrial insulations are tabulated in Table 4 in Chapter 25. Heat transfer film coefficient (or surface coefficient of heat transfer or surface film conductance), h or f. Heat transferred between a surface and a fluid per unit time per unit area driven by a unit temperature difference between the surface and the fluid in con- tact with it, in W/(m 2 ·K). Surface film resistance. The reciprocal of the heat transfer film coefficient, in m 2 ·K/W. Subscripts i and o often denote inside and outside surface resistances and conductances, respectively. The surrounding space must be air or other fluids for convection to take place. If the space is evacuated, the heat flow only occurs by radiation. Thermal resistance R-value, R. Under steady-state conditions, the mean temperature difference between two defined surfaces of material or construction that induces unit heat flow through a unit area, in m 2 ·K/W. Thermal transmittance, U-factor, U. The rate of heat flow per unit area under steady-state conditions from the fluid on the warm side of a barrier to the fluid on the cold side, per unit temperature difference between the two fluids. It is determined by first evaluat- ing the R-value, including the surface film resistances, and then computing its reciprocal, U,inW/(m 2 ·K). The U-factor is some- times called the overall coefficient of heat transfer. In building The preparation of this chapter is assigned to TC 4.4, Building Materials and Building Envelope Performance. 23.1 CHAPTER 23 THERMAL AND MOISTURE CONTROL IN INSULATED ASSEMBLIES—FUNDAMENTALS Terminology and Symbols 23.1 THERMAL INSULATION 23.2 Basic Materials 23.2 Physical Structure and Form 23.2 Properties 23.2 HEAT FLOW 23.4 Factors Affecting Thermal Performance 23.4 Thermal Transmittance 23.6 Factors Affecting Heat Transfer Across Air Spaces 23.7 Calculating Overall Thermal Resistance 23.8 Calculating Interface Temperatures 23.8 Heat Flow Calculations 23.8 INSULATION THICKNESS 23.9 Economic Thickness 23.9 Economic Thickness: Mechanical Systems 23.9 Economic Thickness: Building Envelopes 23.10 MOISTURE IN BUILDINGS 23.11 Moisture Problems in Buildings 23.11 Properties of Water Vapor in Air 23.13 Moisture in Building Materials 23.13 Moisture Migration 23.14 Water Vapor Retarders and Airflow Retarders 23.15 Steady-State Design Tools 23.17 Mathematical Models 23.19 Preventing Surface Condensation 23.20 ROPER DESIGN of space heating, air-conditioning, refrig- Peration, and other industrial systems requires knowledge of thermal insulations and thermal-moisture behavior of building structures. This chapter deals with heat and moisture transfer defi- nitions, fundamentals and properties of thermal insulation materi- als, heat flow calculations, economic thickness of insulation, and the fundamentals of moisture as it relates to building components and systems. TERMINOLOGY AND SYMBOLS The following heat and moisture transfer definitions and sym- bols are commonly used in the building industry. Thermal transmission, heat transfer, or rate of heat flow. The flow of heat energy induced by a temperature difference. Heat may be transferred by conduction, convection, radiation, and mass trans- fer. These can occur separately or in combinations, depending on specific circumstances. Thermal conductivity, k. The time rate of heat flow through a unit area of 1 m thick homogeneous material in a direction perpendicular to isothermal planes, induced by a unit temperature gradient. (ASTM Standard C 168 defines homogeneity.) Units are W/(m·K). Thermal conductivity must be evaluated for a specific mean temperature and moisture content, because in most materials it varies with temperature and moisture content. For porous materials, heat flows by a combination of modes and may depend on orientation, direction, or both. The measured prop- erty of such materials may be called effective or apparent thermal conductivity. The specific test conditions (i.e., sample thickness, orientation, environment, environmental pressure, surface temper- ature, mean temperature, temperature difference, and moisture con- tent) should be reported with the values. With thermal conductivity, the symbol k app is used to denote the lack of pure conduction or to indicate that all values reported are apparent. Thermal resistivity, R u . The reciprocal of thermal conductivity. Units are m·K/W. Thermal conductance, C-factor, C. Thetimerateofheatflow through a unit area of a body induced by a unit temperature differ- ence between the body surfaces. Units are W/(m 2 ·K). When the two defined surfaces of mass-type (i.e., nonreflec- tive) thermal insulation have unequal areas, as in the case of radial heat flow through a curved block or through a pipe cover- ing (see Table 2 in Chapter 3), or through materials of nonuni- form thickness, an appropriate mean area and mean thickness must be given. Heat flow formulas involving materials that are not uniform slabs must contain shape factors to account for the area variation involved. When heat flow occurs by conduction alone, the thermal con- ductance of a material may be obtained by dividing the thermal conductivity of the material by its thickness. When several modes of heat transfer are involved, the apparent or effective thermal conductance may be obtained by dividing the apparent thermal conductivity by the thickness. Where air circulates within or passes through insulation, as it may with low-density fibrous materials, the effective thermal con- ductance is affected. Thermal conductances and resistances of the more common building materials and industrial insulations are tabulated in Table 4 in Chapter 25. Heat transfer film coefficient (or surface coefficient of heat transfer or surface film conductance), h or f. Heat transferred between a surface and a fluid per unit time per unit area driven by a unit temperature difference between the surface and the fluid in con- tact with it, in W/(m 2 ·K). Surface film resistance. The reciprocal of the heat transfer film coefficient, in m 2 ·K/W. Subscripts i and o often denote inside and outside surface resistances and conductances, respectively. The surrounding space must be air or other fluids for convection to take place. If the space is evacuated, the heat flow only occurs by radiation. Thermal resistance R-value, R. Under steady-state conditions, the mean temperature difference between two defined surfaces of material or construction that induces unit heat flow through a unit area, in m 2 ·K/W. Thermal transmittance, U-factor, U. The rate of heat flow per unit area under steady-state conditions from the fluid on the warm side of a barrier to the fluid on the cold side, per unit temperature difference between the two fluids. It is determined by first evaluat- ing the R-value, including the surface film resistances, and then computing its reciprocal, U,inW/(m 2 ·K). The U-factor is some- times called the overall coefficient of heat transfer. In building The preparation of this chapter is assigned to TC 4.4, Building Materials and Building Envelope Performance. 24.1 CHAPTER 24 THERMAL AND MOISTURE CONTROL IN INSULATED ASSEMBLIES—APPLICATIONS GENERAL BUILDING INSULATION PRACTICE 24.1 Wood Frame Construction 24.1 Cold-Formed Steel Frame Construction 24.1 Heavy Steel Frame Construction 24.2 Masonry and Concrete Construction 24.2 Foundation and Floor Systems 24.3 Low-Slope Roof Deck Construction 24.3 Insulation Field Performance Characteristics 24.3 MOISTURE CONTROL IN BUILDINGS 24.3 Control of Liquid Water Entry 24.3 Control of Water Vapor Migration 24.4 Moisture Control Options 24.4 Moisture Control Options for Heating Climates 24.4 Moisture Control Options for Mixed Climates 24.7 Moisture Control Options for Warm, Humid Climates 24.8 Membrane Roof Systems 24.9 Moisture Control in Foundations 24.10 Envelope Component Intersections 24.12 Moisture Control in Commercial and Institutional Buildings 24.12 INDUSTRIAL AND COMMERCIAL INSULATION PRACTICE 24.14 Pipes 24.14 Ducts 24.16 N THE ORIGINAL planning phase of buildings, the thermal and Imoisture design and long-term performance must be considered. Installation of adequate insulation and moisture control assemblies during construction can be much more economical than installation later. Proper selection of thermal insulation and moisture control assemblies must be based on • Thermal and moisture properties of the materials • Other properties required by the location of the materials • Space availability • Compatibility of the materials with adjacent materials • Interior and exterior climate • Performance expectations Types of thermal insulation, their properties, economic thick- ness, and principles of moisture control and moisture transport are discussed in Chapters 23 and 25. Insulation in various assemblies that can be used interchangeably for a given construction, as well as specific moisture control options for various climatic regions, are discussed in this chapter. For specific industrial applications of insulated assemblies see the appropriate chapter in other ASHRAE Handbooks. In the 1998 ASHRAE Handbook—Refrigeration, for refrigerators and freezers, see Chapters 47, 48, and 49; for insula- tion systems for refrigerant piping, see Chapter 32 and this chapter; for refrigerated facility design, see Chapters 13 and 39; for trucks, trailers, and containers, see Chapter 29; for marine refrigeration, see Chapter 30; and for environmental test facilities, see Chapter 37. GENERAL BUILDING INSULATION PRACTICE WOOD FRAME CONSTRUCTION Wood framing members and structural panels such as plywood, particleboard, and fiberboard only provide limited resistance to heat flow; therefore, wood frame construction is well suited to applica- tion of both cavity insulation and surface-applied insulation. The most common materials for cavity insulation are glass fiber, mineral fiber, cellulose, and spray-applied foams. For surface applications, a wide variety of sheathing insulations exists. Roof decks of wood, metal, or preformed units may be insulated on top of or below the deck. Attic construction with conventional rafters and ceiling joists or roof trusses can be insulated between framing members with batt, blanket, or loose-fill insulation. In warm climates, radiant barriers, low emissivity surfaces, and reflective insulations further reduce cooling loads. The Radiant Barrier Attic Fact Sheet (DOE 1991) provides information on climatic areas best suited for radiant barrier applications. This document also provides comparative information on the relative performance of these products versus conventional fibrous insulations. The cavities of cathedral ceiling construction (in which the ceiling insulation and interior finish are parallel to the roof plane) can be insulated using glass fiber, cellulose, rigid foam, or spray-applied insulation. The surface above cathedral ceiling fram- ing may be insulated with insulating panels or structural insulated panels (SIPs). The placement of insulation directly beneath a sloped roof deck in standard flat-ceiling construction, with or without ven- tilation, has been called “cathedralized” construction. The wall cavities of wood frame construction can be insulated with batt, blanket, and loose-fill or spray-applied insulation. When using insulation materials in wall applications, extra care must be taken during the installation to eliminate voids within the wall cav- ity. When installing loose-fill insulation during retrofit of existing construction, all cavities should be checked prior to installation for obstructions such as fire stop headers and wiring that could prevent complete filling of the cavity. In addition, the material must be installed at the manufacturer’s recommended density to ensure the desired thermal performance. In addition to being properly insulated, the exterior envelope of a building should be constructed to minimize airflow into or through the building envelope. Airflow may degrade the thermal perfor- mance of insulation and cause excessive moisture accumulation in the building envelope. The use and function of airflow retarders are discussed in both in Chapter 23 and in this chapter. COLD-FORMED STEEL FRAME CONSTRUCTION Conventional light frame construction with cold-formed steel framing has many characteristics in common with light frame wood construction. The greatest differences are the increased thermal conductivity and the dimension and shape characteristics of steel framing members. Barbour et al. (1994) and Tuluca and Gorthala (1999) found that the conductivity and framing member spacing The preparation of this chapter is assigned to TC 4.4, Building Materials and Building Envelope Performance. . 1 08. 3 56.0 53.7 −42.6 1 08. 3 57.0 54.7 −44.2 1 08. 9 58. 0 55.7 −45.6 1 08. 9 59.0 56 .8 −47.1 109.4 60.0 57 .8 − 48. 3 110.0 65.0 62 .8 a 112 .8 70.0 68. 3 a 116.7 75.0 73.6 a 120.0 80 .0 78. 9 −46 .8 123.9 85 .0. 1 .85 0 .86 80 7.9 1.751 0.1019 70 3.02 0.77 7 98. 4 1.777 0.0996 80 4.76 0.69 788 .7 1 .80 3 0.0973 90 7.25 0.62 7 78. 8 1 .82 8 0.0949 100 10.73 0.56 7 68. 7 1 .85 4 0.0925 110 15.45 0.51 7 58. 3 1 .88 0 0.0901 120. Conductivity, W/(m·K) −73 1.27 3 .8 914.3 0.137 −50 1.39 3 89 7.1 0.133 −25 1.51 2.3 87 8.3 0.1 28 0 1.65 1 .8 859.2 0.124 25 1. 78 1.4 83 9 .8 0.119 50 1.91 1.1 82 0.1 0.114 75 2.04 0 .8 800 0.11 100 2.17 0.7 779.5