Document mmL456LZMLGwRE396B17B5OkQ

204 CHAPTER 9 1950 Guide Heat Transmission Through Building Materials,by F.B. Rowley and A.B. Algren (University of Minnesota, Engineering Experiment station Bulletin No. 8). Building Insulation, by P. D. Close (American Technical Society, Chicago, 1945). Moisture Condensation in Building Walls, by H. W. Viooley (National Bureau of Standards, Report BMB63, December 14, 1940). Condensation of Moisture and Its Relation to Building Construction and Opera tion 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. Transactions, Vol. 45, 1939, p. 545). Simultaneous Heat and Vapor Transfer Characteristics of an Insulating Material, by F. G. Hechler, E. R. McLaughlin and E. R. Queer (A.S.H.V.E. 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). The Diffusion of Water Vapor Through Various Building Materials, by J. D. Babbitt (Canadian Journal of Research, Vol. 17, February, 1939, p. 15). Moisture Migration: A Survey of Theory and Existing Knowledge, by P. F. McDermott (Refrigerating Engineering, August 1941, p. 103). Methods of Moisture Control and Their Application to Building Construction, by F. B. Rowley, A. B. Algren and C. E. Lund (University of Minnesota, Engineering Experiment Station Bulletin No. 17). Permissible Relative Humidities in Humidified Buildings, by Paul D. Close (A S.H.V.E. Journal Section, Heating, Piping and Air Conditioning, December, 1939] p. 766). Condensation Within Walls, by F. B. Rowley, A. B. Algren and C. E. Lund (AB.H.V.E. Transactions, Vol. 44, 1938, p. 95). Permeance Measurement Improved by Special Cell, by F. A. Joy and E. R. Queer (A-S.H.V.E. Journal Section, Heating, Piping and Air Conditioning, June 1949, p. 1(H). CHAPTER 10 INFILTRATION AND VENTILATION Causes of Infiltration, Infiltration Due to Wind Pressure, Infiltration Due to Temperature Difference, Sealing of Vertical Openings, 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 THE air leakage which takes place through various apertures in buildings must be considered in heating and cooling calculations, and properly evaluated. This infiltration as it is sometimes designated takes place through cracks around doors and windows, through solid walls and through fireplaces and chimneys. Although the latter sources of leakage may be considerable, they are often neglected on the assumption that dampers would be closed during periods of extreme cold weather, or else that the fireplace will be in use at such times and will therefore contribute to the heat supplied and lessen the heating load. CAUSES OF INFILTRATION The displacement of heated air in buildings by unheated outside air is due to two causes, namely, (1) the pressure exerted by the wind and (2) the difference in density of outside and inside air because of differences in temperature. The former is generally referred to as infiltration and the latter as stack or chimney effect. In either case an exact estimate of the amount of infiltration under design conditions is difficult to make. The complicating factors include (1) variations in 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 variations in outside temperatures which influence the chimney effect, (5) the relative area and resistance of openings on the windward and leeward sides and on the lower floors and on the upper floors, and (6) the influence of a planned air supply and the related outlet vents. Tight construction is essential for preventing large heat loss due to infiltration. INFILTRATION DUE TO WIND PRESSURE The wind causes a pressure to be exerted on one or two sides of a building. As a result, air comes into the building on the windward side through cracks or porous construction, and a similar quantity of air leaves on the leeward side through like openings. -In general the resistance to air movement is similar on the windward to that on the leeward side. This causes a build ing up of pressure within the building, and a lesser air leakage than that experienced in single wall tests as determined in the laboratory. It is assumed that actual building leakages, owing to this building up of pressure, will be 80 per cent of laboratory test values. While there are cases where this is not true, tests in actual buildings substantiate the factor for the gen- 205