Document NeYMeGjVZw9EL86O8qkg1DjER

112 Chapter 5 '1945 Guide Thecrackmethod is generally regarded-as being-more- accurate-than the- purely-arbitrary air change method, provided the variables entering into the crack method, such as crack width and clearance, can be properly evaluated. Crack Method The crack method is based on known air leakage factors for various types of windows and widths of crack and clearance. The wind velocity and length of crack are also considered when the crack method is employed. The amount, of infiltration for various types of windows is given in Table 22. The fit of double-hung wood windows is determined by crack and clearance. Crack thickness is equivalent to one-half the difference between the inside window frame dimension and the outside sash width: The difference between the width of the window frame guide arid the sash thickness is considered as the clearance. The length of the perimeter Fig. 1. Infiltration Through Various Types of Shingle Construction opening or crack for a double-hung window is equal to three times the width plus two times the height, or in other words, it is the outer sash perimeter length plus the meeting rail length. Not all the window crack in any given room is necessarily used in estimating the infiltration heat loss by the crack method. The length of crack to be selected in any given case depends on jthe number of exposed sides as explained in Chapter 6. Values of leakage shown in Table 2 for the average double-hung wood window were determined by setting the average measured crack and JA.S.H.V.E. Research Reports No. 686--Air Leakage, by F. C. Houghten and G. C. Schrader (A.S.H.V.E. Transactions. Vol. 30. 1924, p. 105). No. 704--Air Leakage Around Window Openings, by C. C. Schrader (A.S.H.V.E. Transactions, Vol. 30. 1924, p. 313). No. 803--Air Leakage on Metal Windows in a Modern Office Building, by F. C. Houghten and M. E. O'Connell (A.S.H.V.E.* Transactions, Vol. 34.1928, p. 321). No. 815--Air Leakage Through a Pivoted Metal Window, by F. C. Houghten and M. E. O'Connell (A.S.H.V.E. Transactions, Vol. 34. 1928. p. 519). No. 817--Effect of Frame Calking and Storm Sash on Infiltration Around and Through Windows, by W. M. Richtmann and C. Braatz (A.S.H.V.E. Transactions, Vol. 34, 1928, p. 547). No. 909--Air Infiltration Through Double-Hung Wood Windows, by G. L. Larson, D. W. Nelson and R. W. Kubasta (A.S.H.V.E. Transactions, Vol. 37, 1931, p. 571). The Weathertightness of Rolled Section Steel Windows, by J. E. Emswiler and W. C. Randall (A.S.H.V.E. Transactions, Vol. 34, 1928, .p. 527). Pressure Differences Across Windows in Relation to Wind Velocity, by J. E. Emswiler and W. C. Randall (A.S.H.V.E. Transactions, Vol. 36, 1930, p. 83). Air Infiltration Through Steel Framed Windows, by D. O. Rusk, V. H. Cherry and L. Boelter (A.S.H.V.E. Transactions, Vol. 39, 1933, p. 169). Air Leakage 113 Table 2. Infiltration Through Windows Expressed in Cubic Feet per Foot of Crock per Hour Ttpz or Window Remarks Wind Velocity, Milk res Hour 5 10 15 20 25 30 Around frame in masonry waB--not calkedb 3 8 14 20 27 Around frame in masonry wall--caBcedb____ 1 2' 3 4 5 Around frame in wood frame conatructionh__ 2 6 11 Double-Hung Wood Sash Total for average window, non-weatbcrstripped, ks-in. crack and k4n. clearance. Windows Includes wood frame leakage^. .. 7 21 39 . (Unlocked) . Ditto, weatherstrippedd 4 13 24 17 23 59 80 36 . 49 Total for poorly fitted window, non-weatherstrippea, kj-iiL crack and kr-in. clearance. Includes wood frame leakaged- _ Ditto, weatherstrippwld' 27 6 Double-Hung Non-weatberstripped, locked Metal Non-weatberetripped, unlocked_____________ Windows! Weatberstripped, unlocked-- 20 20 6 69 19 45 47 19 111 . 154 34 51 70 96 74 104 32 46 199 71 125 137 60 Rolled Section Steel Sash Windows1* Industrial pivoted, 14-in. cracks Architectural projected, krin. crackb______ Architectural projected, krin. crackb______ Residential casement, krin. cnmlri Residential casement, krin- crack*. Heavy casement section, projected, krin. mcVi Heavy casement section, .projected krin. crack! 52 108 15 36 20 52 6 18 14 32 3 10 8 24 176 62 88 33 52 18 38 244 304 86 112 116 152 47 60 76 100 26 36 54 ` 72 Hollow Metal, vertically pivoted window! ___ 30 88 145 186 221 35 6 30 104 63 . 249 92 154 170 76 372 139 182 74 128 48 92 242 "The values given in this table, with the exception of those for double-hung and hollow metal windows, are 20 per cent less than test values to allow for building up of pressure in rooms, and are based on test data reported in the papers listed in chapter footnotes. bThe values given for frame leakage are per foot of sash perimeter as determined for double-hung wood windows. Some of the frame leakage in' masonry walls originates in the brick wall itself and cannot be prevented by calking. For the additional reason that calking is not done perfectly and deteriorates with time, it is considered advisable to choose the masonry frame leakage values for ralkid frames as the average determined by the calked and non-calked tests. cThe fit of the average double-hung wood window was determined as )-in. crack and &-in. clearance by measurements on approximately 600 windows under heating season conditions. dThe values given are the totals for the window opening per foot of sash perimeter and Include frame leakage and so-called elsewhere leakage. The frame leakage values included are for wood frame construction but apply as well to masonry construction assuming a 50 per cent efficiency of frame talking. A Hrin. crack and clearance represent a poorly fitted window, much poorer than average. ^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. . ^Architecturally projected madepfsame sections asfndustrial pivoted except that outside framing member 15 "eavier and it has refinements in weathering and hardware. Used in semi-monumental buildings such as schools. Ventilators swing in or out and are balanced on side arms. )6-in. crack is obtainable in the best practice of manufacture and installation, krin- crack considered ti> represent average practice. `Of same design and section shapes as so-called heavy section casement but of lighter weight. &-in. crack ipsroabcttiacien.able in the best practice of manufacture and installation, krin. crack considered to represent average iMade of heavy sections. Ventilators swing in or out and stay set at any degree of opening. kWn-crack is obtainable in the best practice of manufacture and installation, krin- crack considered to represent average practice. rea80naljle c?re *n installation, leakage at. contacts where windows are attached to steel framefrir a , fat bullions is negligible. With krin. 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 tn the table.