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H.rr American Society of Heating and Ventilating Engineers Guide, 1931 plus the linear feet of sash section in contact with"steel work (at a different leakage rate) at mullions. The crack length for frame windows (when frame is not calked) is the perimeter of the frame. Steel sash frame properly grouted with cement mortar into brickwork or concrete is not to be counted as crack. Leakage through various parts of wood windows is shown by the curves of Fig. 4. The effect of various clearances of wood sash is indicated by the curves of Fig. 5; the value of storm sash is shown by the curves of Figs. 6 and 7. A study of the curves leads to the con- Table 2. Infiltration through Windows Expressed in cubic feet per foot of crock per hour* Type op Window I Won> Velocity, Miles peb Hour 5 10 IS 20 25 30 Chapter 4--Heat Losses by Infiltration that a storm sash is of little value in reducing infiltration when elusion um fitted window, but that a reduction of 50 per cent might tPPZrtoA when storm sash is applied to a poorly fitted or loose window Infdtratkm through door cracks may be assumed to be twice that of window cracks. __...... trnr/\/irrv C/t/vp/lDC Although all authorities do not agree upon the value of the wind veloc ity that should be chosen for any given locality, it is common engineering Around uncalked frame*1............................. 1.4 11.3 22.6 31.1 Double-Hung Wood Sash Around sash, HVln- crack and %4-in. Windows clearance. Plain non-strippedd........... 39.3 84.9 124 161 (unlocked) Average weatherstrippedd.......................... 3 11.7 22.9 34.9 53.6 233 59.6 Double-Hung Non-weatherstripped, locked.... ............ 20 45 70 96 125 154 Metal Non-weatherstripped, unlocked................ 20 47 74 104 137 170 Windows Weatherstripped, unlocked........................ 6 19 32 46 60 76 Pnllori Industrial pivoted/ H6-in. crack.............. Architectural projected,R %4-in. crack.. Residential casement,*1 )42-in. crack.___ Heavy casement section, projected," crack.-- ....................................... 52 20 14 8 108 176 244 304 372 52 88 116 152 208 32 52 76 100 128 24 38 54 72 96 Hollow Metal, vertically pivoted window.... ..................... 30 88 145 186 221 242 "The values given in this table are 20 per cent less than test values to allow for building up of pressure in rooms. \ bPractically all leakage around frames can be.stopped by proper calking. oMost new sash are fitted with crack at least in., which becomes greater as sash dries out and shrinks. Values of the table apply to any window of this type with crack up to K in. dValues given include "elsewhere" leakage through frame but not leakage through uncalked crack around frame. . Windows tested in place in building. 'Industrial pivoted window generally used in industrial buildings. Ventilators horizontally pivoted at center or slightly above, lower part swinging out. . gArchitectural projected made of same sections as industrial pivoted except that outside framing member is heavier, and refinements in weathering and hardware. Used in semi-monumental buildings such as schools. Ventilators swing in or out and are balanced on side arms. lOf same design and section shapes as so-called heavy section casement but of lighter weight. iMade of heavy sections. Ventilators swing in or out and stay set at any degree of opening. - jWith reasonable care in installation, leakage at contacts where window's are attached to steel frame work and at mullions is negligible. With $-in. crack, representing poor installation, leakage at contact with steel framework is about one third, and at mullions about one sixth of that given for industrial pivoted windows in the table. `II 74 Fig. 3. Diagram Illustrating Crack and Clearance practice to use the average wind velocity during the three coldest months of the year.2 Until this point is definitely established the practice of using average values will be followed. Average wind velocities for the months of December, January and February for various cities in the United States and Canada are given in Table 3, Chapter 5. DETERMINATION OF TOTAL AMOUNT OF CRACK The direction of prevailing winds may usually be included within.an angle of about 90 deg. The windows that are to be figured for prevailing and non-prevailing winds will ordinarily each occupy about one-half the perimeter of the structure, the proportion varying to a considerable extent with the plan of the structure, as illustrated by Fig. 8. In tall buildings, infiltration may be considerably influenced by; tem perature difference or chimney effect which will operate to produce a head that will add to the effect of the wind at lower levels and subtract See Pressure Difference across Windows in Relation to Wind Velocity, by Emswiler and Randall [A.S.H.V.E. Journal (Heating, Piping and Air Conditioning). October, 1029]. 75 /n 9