Document V3434KaBLVrKo8qE6Z68Y7edg

416 CHAPTER 23 1965 Guide And Data Book * J. D. Babbitt: The diffuses of water vapor through vari ous building - materials (Canadian Journal of Research, Feb ruary 1939, p. 15). * F. A. Joy aod.D. R. Fairbanks: Effect of unbalanced air pressure on permeance (ASHAE Transactions, Vol. 62, 1956, p. 451). ' W. G. Brown, A. G. Wilson and K. R. Solvason: Heat and moisture Sow through openings by convection (ASHRAE Transactions, Vol. 69,1663, p. 351). ' R. M. Barrer: Diffusion In and Tkrough Solids (Cambridge Press, London, 1951). L. V. Teeedale: Remedial Measures for Building Construc tion (U. 8. Rarest Products Laboratory Report R1710, 1947). * F. B. Rowley, 'A. B. Algren, and C. EL Lund: Methods of Moisture Control and Their Application to Building Construc tion (University of Minnesota, Engineering Experiment Station Bulletin No. l7). u H. J. Barre: The Relation of Wall Construction to Moisture Accumulation in Pill-Type Insulation (Iowa State College of Agriculture and Mechanic Arts, Agricultural Experiment Station Bulletin No. 271, 1940). P. F. McDermott: Moisture migration: a survey of theory and knowledge (Refrigerating Engineering, August 1941, p. 103). u R. L Wray and A. R. Van Vorst: Permeability of paint films to moisture {Industrial and Engineering Chemistry, VoL 25, 1933, p. 842). u R. R. Britton and R. C. Reiebel: ' Water Vapor Trans mission of Building Materials Using Pour Different Testing Methods (U. S. Housing and Home Finance Agency Technical Bulletin No. 12, January 1950). * EL R. Bell, M. G. Seidl, and N. T. Krueger: Water-vapor permeability of building papers and other sheet materials (ASHVE Transactions, VoL 57, 1951, p. 287). " Values from unpublished tests of Pennsylvania State Uni versity, Engineering Experiment Department. 17 F. A. Joy: Basic concepts of water vapor migration and their application to frame walls (ASTM Special Technical Pub lication No. 119, 1951, p. 2). u Condensation Control in Dwelling Constructions (U. 8. Housing and Home Finance Agency, 1949). > Values from Division of Building Research, National Re search Council, Ottawa, to be published. ** How to estimate the amount of water vapor transmitted through building walls (Heating and Ventilating, September 1942). " Water vapor transmission testing (Materials Research Stand ards, February 1961,'p. 117). " J. D. Edwards and D. B. Strohm: Measuring permeability (Modern Packaging Magazine, October 1945). BIBLIOGRAPHY H. W. Wooley: Moisture Condensation tn Building Walls (National Bureau of Standards Report BMS 63, December 14. 1940). . F. B. Rowley, A. B. Algren, and C. E. Lund: Condensation of moisture and its relation to building construction and opera tion (ASHVE Transactions, VoL 45, 1939, p. 231). P. D. Close: Permissible relative humidities in humidified buildings (ASHVE Journal Section, Heating, Piping and Air Conditioning, December 1939, p. 766). F. B. Rowley, A. B. Algren, and C. E. Lund: Condensation within walls (ASHVE Transactions, VoL 44, 1938, p. 95). H. Edenholm: Moisture movement and moisture distribution in the walls of buildings (Meddelanden Fran Statens Porsknmgs- kommatteefor Lantmansiabyggnader No. 5,1945, p. 53, availableas Technical Translation TT-361 from the National R rrh Council of 1952). J. D. Babbitt: Physics of Condensation in Buildings (Na tional Research Council of Canada Bulletin No. 2). ' L. V. Teesdale: Comparative resistance to vapor transmission of various building materials (ASHVE Transactions, Vol. 49, 1943, p. 124). Durability of moisture-resistant membrane materials in con tact with the ground (Housing and Home Finance Agency Housing Research No. 4, October 1952, p. 23). ' Proposed method of test for water vapor transmission of building materials otOiring the Penn Staie-Armstrong cell (ASTM Bulletin No. 215, July 1956, p. 63). Heat and water vapor transmission apparatus for insulated panels (National Bureau of Standards, Technical News Bulle tin, November 1954, p. 157). F. A. Joy and A. W. Sherdon: Automatic permeance measure ment by the permeometer (ASHAE Transactions, Vol. 59 1953, p. 435). ' * F. B. Rowley: A theory covering the transfer of vapor through materials (ASHVE Transactions, Vol. 45, 1939, p. F. G. Hechler, E. R. McLaughlin, and E. R. Queer: Simul taneous heat and vapor transfer characteristics of an insulat ing material (ASHVE Transactions, Vol. 48, 1942, p. 505). J- A. Paxton and N. B. Hutcheon: Moisture migration in a closed, guarded hot plate (ASHVE Transactions, Vol. 58 1952, p. 301). ' C. G. Gurr, T. J. Marshall, and J. T. Hutton: Movement of water in soil due to a temperature gradient (Soil Science. November 1952, p. 335). W. A. Hadley and Ray Eisensiadt: Moisture movement in soils due to temperature difference (ASHAE Transactions Vol. 59, 1953, p7395). K. R. Solvason: Moisture in transient beat flow (ASHAE Transactions, Vol. 62, 1956, p. 111). H. F. Winterkom: Fundamental similarities between electroosmotic and thermo-osmotic phenomena (Proceedings t7th Annual Meeting, Vol. 27, Highway Research Board. 1947, d. 443). S. C. Chang and N. B. Hutcheon: Performance of desiccants in the dry pan test for water vapor permeance of membranes (Canadian Journal of Technology, September 1953, p. 175). F. A. Joy: Thermal conductivity of insulation containing moisture (ASTM Special Technical Publication No. 217, February 1957, p. 65). J. S. Cammerer: The effect of moisture on heat transmission through building and insulating materials (Warms und Kdltetechnih, September 1939, p. 126, available as Technical Trans lation 'it-317 of the National Research Council of Canada. 1952). H. B. Jesperson: Thermal conductivity of moist materials and its measurement (Journal oflHVB, August 1953, p. 157). D. Krischer: Heat conductivity and water vapor diffusion in materials for insulation against cold (Warms und KaUelechnik, 1941, 43(0), p._ 2, translation available from British Build ing Research Station as Library Communication No. 492). D. A. De Vries: The thermal conductivity of soil (Mede- delingen van de Landbouwhogeschool te wageningen, 1952, 52(1). p. 1, translation available from British Bunding Re search Station as Library Communication No. 759). C. H. Johansson: Moisture transmission and moisture dis tribution in building materials (W&rme-Veniilalions-SaniUts- tek, 19 : 67, 1948, available as Technical Translation TT-189 from the National Research Council of Canada). J. D. Babbitt: The movement of moisture through solids (ASTM Bulletin No. 212, February 1956, p. 58). J. R. Philip and D. A. De Vries: Moisture movement in porous materials under temperature gradients (American Geo physical Union Transactions, April 1957, p. 222). . Cold-Storage ~ Facilities: A guide to design and construction (Building Research Advisory Board, National Academy of Sciences--National Research Council, Washington, D. C~ Publi cation 1098,1963). CHAPTER 24 design heat transmission coefficients ... ftonsfer Symbols; Surface Conductance; Soil Cooducfmfy; Ca/cu/ofmg Overoff Coefficients; Overaff Coefficients end " jte,- Practical Use; Computed Coefficients of Walls, Roofs, Ceilings and Floors; Effect of Insulation; Correction for Framing; Ventilated Attics, Foundation Coefficients; Glass Coefficients; Wind Effects; Ca/arfating Surface Temperature*; Conductivity of Industrial /nsufofions; Bare Surface Heat Losses; Heat Flow Calculations for Industrial Insulations THE DESIGN of a heating, refrigerating, or air condi tioning system, including selection of building insulation other fluid. Its value a expressed ia Btu per (hour) (square foot of surface) (Fahrenheit degree temperature difference). Subscripts i and o are usually used to denote inside and outside or firing of piping and ducts, or the evaluation of the thermal surface conductances, respectively. performance of parts of the system, is based on the principles of heat transfer given in Chapter 4. The equations that are m<?gt widely used to estimate the heat transfer loads that are chargeable to the various parts will usually determine the o a thermal conductance of an air space; the time rate of heat flow through a unit area of an air space per unit tempera- tore difference between the boundary surfaces. Its value is ex pressed in Btu per (hour) (square foot of area) (Fahrenheit degree). The conductance of an air space is dependent on the rate of heat transfer under steady-state conditions at design temperatures. For a given part under standard conditions, this rate is a specific value, designated as U, the overall coeffir dent of heat transmission or thermal transmittance. temperature difference, the height, the depth, the position, character, and temperature of the boundary surfaces. Since the relationships are not linear, accurate values must be ob tained by test and not by computation. < = emissivity; the ratio of the total radiant flux emitted by This chapter is concerned with the concepts and procedures a guri*TM* to that emitted by an ideal black body at the same for determining such coefficients, and includes a brief discus sion of factors that may affect the values of these coefficients and the performance of thermal insulations. Coefficients may temperature. E* effective emissivity; the combined effect of the surface emissivities < of the boundary surface of an air space; the boundaries'are assumed to be parallel and of large dimensions as be determined by test or they may be computed from known compared to the distance between them. -- values of the thermal conductance of the various components.' r = surface reflectivity: the ratio of the radiant flux reflected The procedures used for calculating coefficients are illustrated by and, because it is impracticable to test all com binations of materials, tables of computed design values for by an opaque surface to that falling upon it. R thermal resistance; the reciprocal of a heat transfer coefficient, as expressed by U, C, f, or a. Its unit is Fahrenheit degree; per Btu/(hour) (square foot). For example, a wall with the more common constructions are given. a U value of 0.25 would nave a resistance value of R 1/(7 -- 1/0.25 = 4.0 ru. The word ru is being used as an abbreviation HEAT TRANSFER SYMBOLS for resistance unit. U " overall coefficient of heat transmission or thermal trans SURFACE CONDUCTANCE mittance (air-to-air); the time rate of beat flow expressed in Btu per (hour) (square foot) (Fahrenheit degree temperature The convection part of the surface conductance is markedly difference between air on the inside and air on the outside of a wall, floor, roof, or ceiling). The term is applied to the usual combinations of materials, and to single materials, such as affected by air movement. This is illustrated by Fig. 1, which shows the results of tests1'made on 12-in. square samples of window glass, and includes the surface conductance on both-, different materials at a mean temperature of 20 F, and for sides. This term is frequently called the U value. wind velocities up to 40 raph. These conductances inchide'the k = thermal conductivity; the time rate of heat flow through.. a homogeneous material under steady-state conditions, through unit area, per unit temperature gradient in the direction perT ' radiation portion of the coefficient which, for the conditions ; of the tests, was about 0.7 Btu per (hr) (sq ft) (F deg). More pendicular to an isothermal surface. Its unit is Btu per (hour) recent tests' on smooth surfaces show-that surface length also (square foot) (Fahrenheit degree per inch of thickness). Ma significantly affects the convection part of conductance; the terials are considered homogeneous when the value of the thermal , conductivity is not affected by a change in thickness or in area , within the range normally used in construction. Some materials average value decreases as the surface length increases. More over, observations* of the magnitude of low temperature radi- are not isotropic with respect to thermal conductivity. Care . ant energy received from outdoor surroundings show.that should be taken that the test method used is suitable for the. only under certain conditions may the outdoors be treated as particular material and gives a value of conductivity applicable to the intended use. a Nftck body radiating at air temperature. C " thermal conductance per unit area; thermal conductance is usually expressed in KngILA unit* as Btu per (hour) (Fahren THERMAL CONDUCTIVITY OF SOILS heit degree average temperature difference between two sur faces). The hpniinp air-conditioning, and refrigerating engineer, Table 1 gives thermal conductivity values of various soils. however, dealinglargely with compound wails with parallel The effect of texture, moisture content and density are indi- surfaces, makes considerable use of the term unit conductance, or ' cated. Detailed discussion may be found in Reference 4. conductance per unit area, and has therefore continued the use of the term C for conductance. The average temperature is one which adequately approximates that obtained by integrating CALCULATING OVERALL COEFFICIENTS - the temperature of the entire surface. The term is applied to specific materials as used, either homogeneous or heterogeneous; for the thickness or construction stated, not per inch of thickness. The total resistance to heat flow through a flat ceiling, floor, or wall (or a curved surface if the curvature is small) is numeri f = film or surface conductance; the time rate of heat ex cally equal to the sum of the resistances in series.\ change by radiation, conduction, and convection of a unit area of a surface with the surroundings and the surrounding sir or Rr - Ri + R* + B* + ft* + * + 8. , ; .;(}) ffy* Seaenl reapopsUklity lor thi* chapter ia --if---< te TC 2.4. Ittauletioa US Motion Bamera. where Ri, R% etc., are the individual resistances of- the wall components, and Rr is total resistance. 417