Book - School of Science and Technology

Air infiltration 49Table 2.11 Heat requirements for air infiltration through cracks around windowsHeat requirement per unit length of opening window joint (W/mK)Without weather strippingWith weather strippingCountry Urban City Country Urban CityHeight of building (m)OpenWith windbreaksOpenWith windbreaks6 2.43 1.84 1.22 0.75 1.22 0.92 0.61 0.388 2.60 1.98 1.35 0.81 1.30 0.99 0.67 0.4010 2.71 2.10 1.49 0.94 1.36 1.05 0.72 0.4715 3.00 2.33 1.66 1.12 1.49 1.17 0.83 0.5620 3.19 2.52 1.82 1.27 1.59 1.26 0.91 0.6425 3.35 2.67 1.96 1.40 1.68 1.34 0.98 0.7030 3.49 2.80 2.08 1.52 1.75 1.40 1.04 0.7640 3.73 3.03 2.29 1.72 1.86 1.51 1.14 0.8650 3.92 3.21 2.46 1.90 1.96 1.61 1.23 0.95NoteWind speed 8 m/s, at notional height of 10 m in open country, is exceeded for 10% of time only. Other wind speeds derived from this datum.A further adjustment, which should properly be applied also to results derived from airchangecalculations, makes a notional allowance for stack effect in tall buildings. Inwinter, the lower floors will have above average infiltration and although the upper floorswill have less than the average, the 1986 Guide Section A4 proposes that no allowanceshould be made, in the latter case, by deduction. The essence of the method is:. At ground floor level, add the equivalent of 1% for each storey in the building; reducethis addition by 2% for each higher floor, i.e. for a 12-storey building add 12% atground floor level, followed by 10% at first floor, decreasing to 2% at fifth floor withno addition thereafter.This last adjustment results from research work* published in 1961 which concludedspecifically that:. Swinging door entrances ± for a particular set of conditions ± infiltrate about 25 m 3through a single opening, per person entering or leaving a building, and 15 m 3 perperson for a vestibule-type entrance.. Revolving doors under similar conditions infiltrate about 2 m 3 per person, and motordriven doors about half that amount.. Adequate heating in winter is required in entrances and vestibules at ground floor levelby forced warm air heaters or air curtains, augmented by floor panel heating.The 1999 Guide Section A4 proposes an equation for calculating the pressure differencerelated to vertical height differences and hence the airflow through openings.Reference must also be made here to significant problems which have been encounteredwith buildings clad in curtain walling. As may be seen from Figure 2.11, if particular carehas not been taken to seal the structural joint where the cladding passes the edge beam ofthe floor slab, leakage can occur and stack effect will cause air to move upwards, floor by* Min, T. C., `Engineering concept and design of controlling ventilation and traffic through entrances intall commercial buildings', JIHVE, 1961.