Book - School of Science and Technology

50 The building in winterIntermediatefloor slabIntermediatefloor slabVoidLight weightinsulatedinfill panelVoidCold bridgeat mullionCold bridgeat mullionand transomsSingleglazingDoubleglazingInfill panelInner skinHeater/unitcasing(a)(b)Figure 2.11 Examples of curtain wallingfloor in cascade. A further example of air flow from an unexpected source can arise wherewind pressure is applied to small openings in curtain wall cladding, such as drillings inmembers provided to drain away condensation, with uncontrolled infiltration to voidsabove suspended ceilings and consequent excess heat loss. The criteria for tightness of thebuilding envelopes have to some extent been established and the conclusion reached thatsite workmanship is the major influence.ApplicationTaking, once again, the simple space shown in Figure 2.3 and an air-to-air temperaturedifference of 22 K as before, the infiltration loss on an air-change basis would be:Room volume14:5 8:5 4 ˆ 4936:0 8:5 4 ˆ 204 697 m 3from Table 2.9, allowing for windows on two sides without weather stripping, take 1 1 ¤ 2 airchanges or a ventilation allowance of 0:5 W/m 3 K. Thus,697 0:5 22 ˆ 7667 Wand, in terms of floor area for unit temperature difference,(697 0:5)/419 ˆ 0:83 W/m 2 K