Buildings Guide

Building Envelope  »  Air tightness


Unwanted air transfer taking place through gaps and cracks in the building fabric is common in most conventional buildings. In cold climates, air leakage can contribute 40% or more of the total heating load during of the building winter. In summer or in warm climates in general, this effect is a little more moderate. This is because the air exchange between inside and outside is increased by larger temperature differences between inside and outside which is the case in cold winters. The pressure difference between the top and the bottom of the building is greater here than in hot conditions. In winter the temperature difference between inside and outside might be 21K (+20 °C inside and -1 °C outside) and in summer or any other warm climate the difference might only be 12K (inside 25°C and outside 37 °C). Controlling air leakage leads to savings in cooling and heating energy. For example, in the dry climate of Tehran, the cooling load can be reduced by about 12% with an envelope that is twice as tight as the average. When the building is well insulated and shaded, this fraction would be higher, though (Harvey, 2006).

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