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226 CHAPTER 10 1956 Guide Remedial Measures for Building Construction, by L. V. TeesdaJe (Report R1710 of V. S. Forest Products Laboratory 1947). T Methods of Moisture Control and Their Application to Building Construction, by F. B. Rowley, A. B. Algren and C. E. Lund (Clnivemty of Minnesota, Engineering Experiment Station Bulletin No. 17). 8 The Relation of Wall Construction to Moisture Accumulation in Pill-Type Insulation by Henry J. Barre (Iowa State College of Agriculture and Mechanic Arts Agricultural Experiment Station Bulletin No. 271, 1940). ' Moisture Migration: A Survey of Theory and Existing Knowledge, by P. F. McDermott (Refrigerating Engineering, August 1941, p. 103). ip Permeability of Paint Films to Moisture, by R. I. Wray and A.- R. Van Vorst (Industrial and Engineer ing Chemistry Vol. 25, p. 842, 1933). 1J Water Vapor Transmission of Building Materials Using Four Different Testing Methods, by R. R. Britton and R. C. Reichel, (U. S. Housing and Home Finance Agency Technical Bulletin No. 12, January 1950). ** Water-Vapor Permeability of Building Papers and Other Sheet Materials, by E. R. Bell, M. G. Seidl, and N. T. Krueger (A.S.H.V.E. Transactions, Vol. 57, 1951, p. 287), t* Value from unpublished tests of Pennsylvania State College Engineering Experiment Station. 14 Condensation Control in Dwelling Constructions (U. S. Housing and Home Finance Agency, 1949). BIBLIOGRAPHY MoistureCondensation in Building Walls, by H. W. Wooley (National Bureau of Standards, Report BMSO 3 December 14, 1940). Condensation of Moisture and Its Relation to Building Construction and Operation, by F. B. Rowley, A. B. Algren and C. E. Lund (A.S.H.V.E. Transactions, .Vol. 45, 1939, p. 231). A Theory Covering the Transfer of Vapor Through Materials, by F. B. Rowley (A.S.H.V.E. Transac tions, Vol. 45, 1939, p. 545). Simultaneous Heat and Vapor Transfer Characteristics of an Insulating Material,, by F. G. Hecbler, E. R. McLaughlin and E. R. Queer (A.S.H.VJE. Transactions, Vol. 48, 1942; p. 505). Comparative Resistance to Vapor Transmission of Various Building Materials, by L. V. Teesdale (A.S.H.V.E. Transactions, Vol. 49, 1943, p. 124). Permissible Relative Humidities in Humidified Buildings, by Paul D. Close (A.S.H.V.E. Journal Section, Heating, Piping and Atr Conditioning, Deoember, 1939, p. 766). Condensation Within Walls, by F. B. Rowley, A-. B. Algren and C. E. Lund (A.S.H. V.E. Transactions, Vol. 44, 1938, p. 95). Physics of Condensation in Buildings, by J. D. Babbitt (Bulletin No.-2, National Research Council, of Canada). Wood Handbook (Forest Products Laboratory, United States Department of Agriculture, 1940). Studies of the Physical Properties of Hardened Portland Cement Paste by T. C. Powers and T. L. Brownyard (Journal, American Concrete Institute, Vol. 18, No. 8, April 1947, p. 933). Experiments on the Freezing of Certain Building Materials by W. N. Thomas (Building Research, Tech nical Paper No. 17, H.M.S.O.TLondon, 1938). Moisture Migration in a Closed, Guarded Hot Plate by J. A. Paxton end N. B. Hutcheon (A.S.H.VJ3. Transactions, vol. 58, 1952,,p. 301). Movement of Water in Soil Due to a Temperature Gradient by C. G. Gurr, T. J. Marshall, and J. T. Hutton (Soil Science, Vol. 74,. No. 5, November, 1952, p. 335). Fundamental Similarities Between Electro-osmotic and Thermo-osmotic Phenomena by H. F. Winter- korn (Proceedings 87th Annual Meeting, Highway Research Board, Vol. 27, 1947, p. 443). Performance of Desiccants in the Dry Pan Test for Water Vapor Permeance of Membranes by S. C. Chang and N. B. Hutcheon (Canadian Journal of Technology, 31, September, 1953, p. 175-192.) Fundamental Considerations in the Design of Exterior Walls for Buildings by N. B. Hutcheon (Technical Report No. 13, D.B.R., National Research Council of Canada, 1953). CHAPTER 11 INFILTRATION AND VENTILATION Causes of Infiltration, Infiltration Due to Wind Pressure, Infiltration Due to Temperature Difference, Sealing of Vertical Openings, Infiltration Meas urement, Natural Ventilation, Wind Forces, Temperature Difference Forces, Heat Removal, Effect of Unequal Openings, Combined Wind and Temperature Forces, Types of Openings, General Ventilation Rules, Ventilation of Animal Shelters, Garage Ventilation Infiltration is the air leakage through cracks and interstices, around windows and doors, and through floors and walls. Its magnitude depends on the structural design, workmanship, and condition of the building. The rate of infiltration cannot be controlled by the inhabitants of the building to any considerable extent. Natural ventilation is the controlled displace ment of air through openings, such as windows, doors and ventilators as well as through combustion heating devices. CAUSES OF INFILTRATION The air leakage which takes place through various apertures in buildings must be estimated in heating and cooling calculations and enough heating or cooling capacity provided to offset the heat lost or gained by the air leakage. The rate of air flow into and out of a building depends on the magnitude of the pressure difference between the inside and outside of the structure and on the resistances presented to this pressure difference. The pressure difference exerted on the building walls by the air may be caused either by wind or by a difference in density of the air inside and outside the building. The effect of the wind depends on the interrelation of the speed and direction of the wind and the exposure of the building. The effect of the difference in the density of the air depends on the magnitude of the inside-outside temperature difference, the height of the rooms, the shape of the openings, and their elevation in the room or building. The effect of the difference in density is often referred to as the chimney or stack effect. The pattern of air flow through any part of the structure de pends on both the pressure difference and the openings. In general, when the pressure difference is the' result of wind pressure, air will enter the building through openings in the windward walls and leave through open ings in the leeward walls or through ventilating ducts in the roof. When the pressure difference is caused by the inside-outside temperature differ ence 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-conditioned building. An exact estimate of the amount of infiltration under design conditions Is difficult to make. The complicating factors include (1) variations m building construction, particularly as to width of crack or size of openings through which air leakage takes place; (2) the variations in wind velocity and direction; (3) the exposure of the building with respect to air leakage openings, and with respect to adjoining buildings; (4) the 227