Document kD9ZLK6ZjXGwKkEXrj61YVp9J

American Society of Heating and Ventilating Engineers Guide, 1932 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 crack per houra Tip of Window Wind Velocitt, Moss per Hour 5 10 15 20 . 25 30 Around uncalked frame*1.......................... 1.4 11.3 22.6 31.1 -- 53.6 Double-Hung Wood Sash Around sash, H6-in- crack and Windows clearance. Plain non-strippedd.......... 39.3 84.9 124 161 -- 233 (unlocked) Average weatherstrippedd....................... 3 11.7 22.9 34.9 -- 59.6 Double-Hung Non-weatherstripped, locked-- .......... 20 45 70 96 125 154 Metal Non-weatherstripped, unlocked--......... 20 47 74 104 137 170 Windowse Weatherstripped, unlocked..... ...........-- 6 19 32 46 60 76 Rolled Section Steel Sash Windows! Industrial pivoted/ ife-in. crack--........ Architectural projected. %4-in. crack.. Residential casement,*1 crack--_. Heavy casement section, projected,1 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. cMost new sash are fitted with crack at least H# 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 M, in. dValues given include "elsewhere" leakage through frame but not leakage through uncalked crack around frame. Windows tested in place in building. findustrial pivoted window generally used in industrial buildings. Ventilators horizontally pivoted at center or slightly above, lower part swinging out. sArchitectural 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. hOf 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. iWitfa reasonable care in installation, leakage at contacts where windows 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. 74 ..Chapter 4--Air Leakage from Buildings elusion that a storm sash is of little value in reducing infiltration when applied to a well fitted window, but that a reduction of 50 per cent might be expected when storm sash is applied to a poorly fitted or loose window. Infiltration through door cracks may be assumed to be twice that of window cracks. WIND VELOCITY FACTORS 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 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 2. 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. (See discussion of wind movement in Chapter 2). AMOUNT OF CRACK TO USE In no case should the amount of crack used for computation be less than half of the total crack in the outside walls of the room. Thus, in a *Sc*! Pressure Difference across Windows in Relation to Wind Velocity, by Emswilcr and. Randall (A.S.H.V.E. Transactions, Vol. 36, 1930). 75