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102 CHAPTER 8 1960 Guide MH. M. Lemon, H. Wise, and M. Hamburger: Bacteria] content of air in army barracks (War Medicine 6:92,1944). "O. H. Robertson, M. Hamburger, C. G. Loodi, T. T. Puck, and H. M. Lemon: A study of the nature and control of air borne infection in army camps {Journal of the American Medi cal Association 128:993, 1944). **0. H. Robertson et ai: Lethal effects of triethylene glycol vapor on air-borne bacteria and influenza virus (Science 97: 142, 1943). . " M. Hamburger, Jr, O. H. Robertson, and T. T. Puck: Tire present status of glycol vapors in air sterilisation (American journal of the Meaical Science* 209:162,1945). ' "T. N. Harris and J. Stokes, Jr.: Summary of a 3-year study of the clinical applications of the disinfection of air by glycol vapors (American Journal of the Medical Sciences 209:152, 1945). B William Lester, Jr, Saul Kaye, O. H. Robertson, and Ed ward Dunklin: Factors of importance in the use of triethylene glycol vapor for aerial disinfection (American Journal of Pub lic Health 40:813, July l, 1950). ** Edward Bigg, B. H. Jennings, and F. C. W. Olaon: Triethylene glycol vapor distribution for air sterilisation (ASHVE Transactions, VoL 53, 1947, p. 393). * Glycol vapors for disinfecting purposes (Journal of the American Medical Association 133:696, March 8, 1947)1 ** W. J. McConnell: An experiment with triethylene glycol vapor for the control.of colds among office employees {In dustrial Medicine 18:5, page 192), " S. M. Wheeler, H.'S. Ingraham, A. Hollaender, N. D. T.ill, J. Gershon-Cohen, and E. W. Brown; Ultra-violet light con trol of airborne infections in a naval training center (American Journal of Public Health, Vol. 35,1945, p. 457). " H. G. DuBuy, J. E. Dun, F. S. Brackett, W. C. Dresses, P. A. Nealand, and L Possner: An evaluation of ultraviolet radiation of sleeping quarters as supplement of accepted meth ods of disease control (American Journal of Hygiene, Septem ber 1948, p. 207). 0 Recent studies on disinfection of air in military establish ments (American Journal of Public Health, February 1947, p. 189). ** Commercial exploitation of glycol vaporisers (American Journal of Public Health, February 1949, p. 222). **N. Pace, 'M. B. Fisher, J. E. Birren, G. C. Pitts, W. A. White, Jr., W. V. Consolasio, and L. J. Pecora: A Comparative Study of the Effect on Men of Continuous Versus Intermittent Exposure to a Tropical Environment (Research Project X-205, Naval Medical Research Institute Report No. 2, May 1915). *F. K. Hick and M. M. Montgomery: Mechanism of Heat Retention (unpublished). 0 A. R. Behnke; Environmental and Physiologic Studies Aboard an Air-Cooled Hospital Ship Bn Route from Norfolk, Virginia, to Canal Zone {USS. Tranquility, AH-14, June fl-13 1945) (Research Project X-205, Naval Medical Research In stitute Report No. 4, September 1945). G. E. Burch: The influence of environmental temperature and relative humidity on the rate of water loss through the dun in oongestive heart failure in a subtropical dimate (Ameri can Journal of Medical Science, Vol. 211, 1946, p. 181). G. Berensoa and G. E. Burch: Tbe responses of patients.with oongestive heart failure to rapid elevation in atmospheric temperature and humidity (American Journal of Medical Science, Vol. 223, 1952, p. 45). " Gunner Edstrom, G. Lundin, and T. Wramer: Investiga tion into the effect of hot, dry microclimate on peripheral circulation in arthritic patients {Armais of Rheumatic Diseases 7:76, June 1948). M Fundamentals of Anesthesia (American Medical Associa tion Press, Chicago, 1944, 2nd ed., p. 204). " B. A. Green: The hazard of fire and explosion in anesthesia (Anesthesiology 2:144, 1941). " R. M. Toveli and A. W. Friend: Control of physical haz ards of anesthesia (Canadian Medical Association Journal 46: 560, 1942). 0 F. C. Houghten and W. L. Cook, Jr.: ASHAE Research Repost No. 1111--Air conditioning requirements of an operat ing room and recovery ward (ASHVE Transactions, Vol. 45, 1939, p. 161). ** A. R. Behnke and O. Schneider: Unpublished naval stud ies (1940). *C. P. Yaglou and Ursula Wilson: Disinfection of Air by Air Conditioning Processes (American Association for the Advancement of Science, Publication No. 17, p. 129). * J. A. Reyniers: The control of cross-contamination by the use of mechanical barriers (American Association for the Ad vancement of Science, Aerobiology 17:254, 1942). "K.D. Blaekfan, C. P. Yaglou, and K. McKenzie: Tbe pre mature infant: a study of the effect of'atmospheric conditions on growth and on development (American Journal Diseases of Children 46:1175, 1933). UI. Rosenstern: Observations on the control of respiratory contagion in the cradle (American Association for the Advance ment of Science, Aerobiology 17:242, 1942). **F. H. Krusen; Physical Medicine (W. B. Saunders Co., Philadelphia, 1941). *F. C. Houghtea, M. B. Federber, and Cart Cutberlet: ASHVE Research Report No. 1054--Fever therapy induced by conditioned air (ASHVE Transactions, Vol. 46, 1940. p. 131). M. B. Federber, F. C. Houghtea, and Carl Gutberiet: ASHVE Research Report No. 1161--Fever therapy locally induced by conditioned air (ASHVE Transactions, Vol. 46. 1940, p. 307). " L. W. Crossman and S. K. Safford: Refrigeration for an esthesia and therapy {The Modem Hospital 64:86, 1945). **B. Z. Rappaport, T. Nelson, and W. H. Welker: The ef fect. of low relative humidity and constant temperature on pollen asthma {Journal of Allergy 6:111, 1935). 0 C, P. Yaglou: Hospital air conditioning (The Environment and Its Effect Upon Man, Harvard School of Public Health, 1939, p. 244). " A. L. Barach: Principles and Practices of Inhalational Therapy (J. B.(Lippincott Co., Philadelphia, 1944). "Cyril Tasker: What are the right conditions for comfort cooling? {Heating, Piping and Air Conditioning, August 1948, p- 84). "C. P. McCord and W. R. Witheridce: Odors Physiology and Control (McGraw-Hill Book Co., New York, 1949). BIBLIOGRAPHY R. P. Gaulin: Air conditioning the hospital (Reference Sec tion, Air Conditioning, Heating & Ventilating, January 1957, p. 73). . W. W. Treichler, Jr.: Air conditioning the operating room (Air Conditional, Heating <fc Ventilatmp, April 1957, p. 73). } CHAPTER 9 HEAT TRANSMISSION COEFFICIENTS OF BUILDING MATERIALS Heat Transfer Symbol* Calculating Overall Coefficients,- Conductivity of Homogeneous Materials} Soil Conductivity and Specific Heat,- Surfoce and Air Space Conductance; Overall Coefficient* and Their Practical Use; Computed Coefficients of Walls, Roofs, Ceilings, and Floors; Effect of Insulation} Combined Ceiling, Roof, and Floor Coefficient* Glass Coefficient* CoJcufaring Surface Temperature* THE design of air-conditioning or beating systems for buildings requires a knowledge of the thermal properties 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. of the walls enclosing the space. (The term mafia in this case, emissivity; the ratio of tbe total radiant flux emitted by includes windows, doors, ceilings, floors, roofs, and skylights.) a surface to that emitted by an ideal black body at the same The rate of heat flow through (he walls under steady-state temperature. conditions at design temperatures is usually the basis for cal culating the heat required. For a given wall under standard conditions the rate is a specific value designated as U, the optrail coefficient of heat transmission or thermal transmittance. It may be determined by test in a guarded hot box apparatus, E *= effective emissivity; the combined effect of tbe surface emissivities of the boundary surfaces of an air space; the boundaries assumed to be parallel and of large dimensions as compared to the distance between them. r ~ surface reflectivity; the ratio of the radiant flux reflected by an opaque surface to that falling upon it. or it may be computed from known values of the thermal conductance of the various components. Because it is imprac ticable to test all combinations of building materials, the pro cedure and necessary data for calculation of the value of U are given in this chapter, together with convenient tables of R ** thermal resistance. Its value is obtained from the re ciprocal of heat transfer as expressed by U, C, /, or a. It may be expressed in (Fahrenheit degrees per Btu)/(bour) (square foot). For example, a wall with a U value of 0.25 would have a resistance value of R * 1/0.25 =* 4.0 rv. The word ru has been suggested as an abbreviation for resistance unit. computed values for a large number of the more common constructions. CALCULATING OVERALL COEFFICIENTS HEAT TRANSFER SYMBOLS U -- overall coefficient of heat transmission or thermal trans mittance (air-to-air); the time rate of heat flow expressed in Btu per (hour) (square foot) (Fahrenheit degree temperature difference between air on tbe inside and air on tbe outside of a wall, floor, roof, or ceiling). The term is applied to tbe usual combinations of materials, and also to single materials, such as window glass, and includes the surface conductance on both sides. This term is frequently called the U value. k thermal conductivity' the time rate of heat flow through a homogeneous material under* steady conditions per unit tem perature gradient through unit area perpendicular to the tem perature gradient. Its value is expressed in Btu per (hour) (square foot) (Fahrenheit degree per inch of thickness). Mate rials are considered homogeneous when tbe value of k is not af fected by variation in thickness or size of sample within tbe range normally used in construction. C - thermal conductance; tbe time rate of beat flow through a unit area of a material from ODe of its surfaces to the other per unit temperature difference between the two surfaces. Its value is expressed in Btu per (hour) (square foot) (Fahrenheit de gree). The term is applied to specific materials as used, either homogeneous or heterogeneous, for the thickness or construc tion stated, not per inch of thickness. / " film or surface conductance; the time rate of heat ex change by radiation conduction and convection of a unit area of a surface with the surroundings and the surrounding air or other fluid. Its value is expressed in Btu per (hour) (square foot of surface) (Fahrenheit degree temperature difference). Subscripts i and o are usually used to denote inside and outside surface conductances, respectively. a * thermal conductance of an air space; the time rate of beat flow through a unit area of an air space per unit tempera ture 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 tbe temperature difference, the height, the depth, the position. From Chapter 5, Equation 7, the total resistance to heat flow through a wail is equal numerically to the sum of the resistances in series. Rr * Ri + Rx + Rt + R + + fi* (1) where Rt, ft,, etc., are the individual resistances of the wall components, and Rr is total resistance. For a wall of a single homogeneous material of conduct ivity k and thickness x with surface coefficients f< and /., Then by definition, U -- 1/Rr ' For a wall with air space construction and consisting of two homogeneous materials of conductivities hi and k\, thick nesses X\ and zi, respectively, and separated by an air space of conductance a. Rt 7 + I+-` + ^ /< * a Jfcj (3) and U = 1/fir For types of building materials having non-uniform or ir regular sections such as hollow clay tile or concrete blocks, it is necessary to use tbe conductance C of the section unit as manufactured instead of a conductivity k. The resistance of the section 1/C is therefore substituted for x/k in Equations 2 and 3. It will be noted that in order to compute the U value of a construction it is first necessary to know the conductivity 103