Document wDLzdYb7QY0kGmMmvEaqZ5J1J

454 CHAPTER 24 No. 914--F. B. Rowley and W. A. Eckley: Surface coefficients as affected by direction of wind (ASHVE Transactions, VqL 38, 1932, p. 33). No. 916--F. C. Houghten and Carl Gutberlet: Conductivity of concrete (ASHVE Transactions, VoL 38,1932, p. 47). No. 964--F. B. Rowley: The heat conductivity of wood at climatic temperature differences (ASHVE Transact!onb, VoL 39, 1933, p. 329), No. 966--F. B. Rowley: Insulating value of bright metallic surfaces (ASHVE Transactions, VoL 40,1934, p. 413). No. 1026--F. B. Rowley, A. B. Algren, and Clifford Carlson: Thermal properties of concrete construction (ASHVE Trans actions, Vol. 42, 1936, p. 33). No. 1048--F. B. Rowley, A. B. Algren, and Robert Lander: Thermal properties of concrete construction (ASHVE Trans actions, VoL 43, 1937, p. 33). No. 1351--G. V. Parmelee and W. W. Aubele: Overall coeffi cients for flat gl*" determined under natural weather condi tions (ASHVE Transactions, VoL 65,. 1949, p. 39). G. B. Wilkes and C. M. F. Peterson: Radiation and convec tion across air spaces in frame construction ASHVE Trans actions, VoL 43, 1937, p. 351). L. W. Schad: Tnuluting effect of successive air space bounded by bright metallic surfaces (ASHVE Transactions, V6L 37, 1931, p. 285). J. D. MacLean: Thermal conductivity of wood (ASHVE Transactions, VoL 47, 1941, p. 323). G. B. Wilkes and C. O. Wood: The specific heat of thermal iixnilntmg (ASHVE TRANSACTIONS, VoL 48, 1942, p. 493). D. B. Anderson: Heat loss studies in four identical buildings to determine the effect of insulation (ASHVE Transactions, VoL 48,1942, p. 471). Standard Method of Test for Thermal Conductivity by Means of the Guarded Hat Plate, sponsored by ASHVE, ASTM, ASRE, and NRC, and approved as a tentative code by ASHVE and ASTM in 1942 (ASTM designation C-177-45, Approved, 1945). G. B. Wilkes and C. M. F. Peterson: Radiation and convec tion from surfaces in various positions (ASHVE Transac tions, VoL 44,1938, p. 513). B. F. Raber and F. W. Hutchinson: Radiation corrections for basic constants used in the design of ail types of heating systems (ASHVE Transactions, VoL 51, 1945, p. 213). H. E. Robinson, F. J. Powiitchj and R. 8. Dill: The Thermal Insulating Value of Airspaces (Housing and Home finance Agency, Housing Research Paper No. 32, U. 8. Government Printing Office, 1954). 1965 Guide And Data Book C. B. Wilkes, K. G. Hechier, and E. R. Queer:-inermal test coefficients of aluminum insulation for buildings (ASHAE Transactions, VoL 46, 1940, p. 109). T. D. Phillips: Effect of Ceiling Insulation upon Summer Comfort (National Bureau of Standards Report BMS52, July 1 1940). L. V. Teesdale: Thermal Insulation Made of Wood-Base Materials, Its Application and Use in Houses (U. S. Forest Products Laboratory Report No. R1740, October 1949). F. B. Rowley and A. B. Algren: Heat Transmission through Budding Materials (University of Minnesota, Engineering Ex periment Station Bulletin No. 8). Paul D. Close: Building Insulation (American Technical Society, Chicago, 1951, 4th ed.). F. C. Houghtan and Carl Gutberlet: Beat emission from iron and copper pipe (ASHVE Transactions, VoL 39, 1938, p. 97). Heal Transmission from Surfaces (Philip Carey Mfg. Co., Bulletin 102-A). R. EL Heflman: 8urface heat transmission (Sec. 1, Mechanical Engineering, May 1929, p. 355). - S. Crocker: Piping Handbook (McGraw-Hill Book Co., New York, 1945, 4th ed.). P. Swain: Insulation handbook (Power, VoL 94, Nos. 2, 3, 5, 7, and 9, 1950). U. W. Smith: How to insulate equipment (Plant Engineering, VoL 1/December 1947, p. 32). T. S. Nickerson and G. M. Dusinberre: Heat transfer through thick insulation on cylindrical enclosures (ASME Transactions, Vol. 70, 1948, p. 903). H. J. Stoever: Applied Heat Transmiesicn (McGraw-Hill Book Co., New York, 1941). * F. B. Rowley, R. C. Jordan, and R. M. Lnnder: Thermal con ductivity of inmiluting materials at low mean temperatures (Refrigerating Engineering, December 1945, p. 541). F. B. Rowley, R. C. Jordan, and R. M. Tnnder: Low mean temperature thermal conductivity studies (Refrigerating Engineering, January 1947, p. 35). J. D. Verschoor: Thermal conductivity of commercial insula tions'at low temperatures (Refrigerating Engineering, September 1954, p. 35). G. B. Wilkes: Thermal conductivity,, expansion and specific heatof insulatoreatextremely low temperatures (Refrigerating Enigneeeing, July 1946, p. 37). Simplified Practice Recommendation for Thermal Conductance Factorsfor Preformed Above-Deck Roof Insulation (No. R257-55, U. S. Department of Commerce, Washington, D. C., 1955). CHAPTER 25 INFILTRATION AND VENTILATION Wind Forces, Temperature Difference Forces, Combined Forces, Calculation of Infiltration, Air Leakage Through Windows, Doors, and Walls, Natural Ventilation, Flow Due to Wind, Flow Due to Temperature Difference, Flow Due to Combined Wind and Stack Effect, Types of Openings, General Ventilation Rules INFILTRATION is the air leakage through cracks and interstices, around windows and doors, and through floors and walls of a building of any type from a low onestory house or commercial building to a multistory sky scraper. The magnitude of infiltration depends on the type of construction, workmanship, and condition of the building. The rate of infiltration cannot be controlled by the inhabi head of the industurbed air stream. The velocity head equiva lent to a given wind speed can be expressed as: p. = 0.000482 Vm* (1) where p, " velocity head, inches water gage. Vm = wind velocity, miles per hour. tants of tire building to any considerable extent. Natural ventilation is the intentional displacement of air through specified openings, such as windows, doors, and by vent ilators. . The rate of air Sow into and out of a building due to either infiltration, exfiltration, or natural ventilation, depends on the magnitude of the pressure difference between the inside and outside of the structure and on the resistances to flow of air offered by openings and interstices in the building. The pres sure difference exerted on the building enclosure by the air may be caused either by wind or by a difference in density of the air inside and outside. The effect of the difference in density is often called chimney or stack effect and is often the major factor. The pattern of air flow through any part of the structure depends on both the pressure difference and the area - - Equation 1 is based on an air density of 0.075 lb per cu ft Values of the velocity head and velocity in fpm are given in Fig. 1. The choice of values of static pressure around buildings for use in calculations must be somewhat arbitrary due to the number of variables and the limitations in available informa tion. Pressures may vary from + 0.5 to + 0.9p, on the wind ward side, and from -- 0.3 to -- O.Op. on the leeward tide for rimplft square or rectangular shaped buildings, depending on the angle of the wind. Pressures on the other tides, parallel to, or at slight angles to the wind direction, may range from -- 0.1 to -- 0.9p,. These surfaces when curved may act as airfoils, resulting in negative pressures two or more times the velocity head of the free air stream. Pressures over roof sur- of openings. When the pressure difference is the result of wind pressure, air will enter the building through openings in the windward walls and leave through openings in the lee ward walls or through ventilating ducts in the roof as may be the case of one-story commercial buildings. When the pres sure difference is caused by the' indoor-outdoor temperature difference, the flow will be along the path of least resistance from inlets at lower levels to outlets at higher levels in a heated building or in the opposite direction for an air-con ditioned building, as may be the case of multistory sky scrapers. In most instances the pressure difference between inside and outside will result from temperature difference forces. Mechanical ventilation and exhaust systems *n affect pres sure differences across the building enclosure, depending on the design. WIND FORCES Air flow due to wind around and over a building creates regions in which the static pressure is either above or below the static pressure in the undisturbed air stream. In general, pressures are positive on the windward side resulting in inflow of air and negative on the leeward side resulting in outflow of air. Pressures on the remaining sides may be negative or posi tive depending on the angle of the wind. The static pressure pattern over a roof will depend on the roof type. Pressures are generally negative over flat or low-pitched roofs, but may be positive on the windward side and negative on the leeward tide of high-pitched roofs. Static pressures over the surfaces of buildings are approximately, proportional to the velocity n, `H** cenm) wpoaijbflity (or (Us chapter is ---`f--1 to TC U, Vonta2tfa **Owwneot sod Infiltration. fig. 1 .... Wind vs Velocity Pressure end Velocity in FPM' 455 /