Air leak control
Introduction
The tightness of a building (also called airtightness) can be defined as the resistance to air leakage inward or outward through unintentional leak points or areas in the building envelope. This air leak is driven by differential pressures across the envelope due to the combination of the stack effect, external wind, and mechanical ventilation systems.[1].
Airtightness is the fundamental property of a building that affects infiltration and exfiltration (the uncontrolled leak of outside air into and out through cracks, gaps or other unintentional openings in a building, caused by the effects of wind pressure and/or the stack effect).[2].
An airtight construction has several positive impacts[3] when combined with an appropriate ventilation system (whether natural, mechanical or hybrid):[4].
From an energy point of view, it is almost always desirable to increase air tightness, but if infiltration provides a useful dilution of indoor pollutants, indoor air quality may be affected. However, it may not be so clear how useful this dilution is as leaks in buildings cause uncontrolled air flows and potentially poorly ventilated rooms, although the building's total air exchange rate may be sufficient. This adverse effect has been confirmed by numerical simulations in the French context that have shown that typical mechanical ventilation systems produce better indoor air quality with more airtight envelopes.[7].
Air leakage through the enclosure from the relatively warm and humid side to the relatively cold and dry side can cause condensation and related damage as its temperature drops below the dew point. [8] [9].
Air leak paths
Leaks usually occur in the following places in the building envelope: [10].
The most common leak sites are listed in the figure and explained below:.
Metrics
The tightness of a building is usually expressed in terms of the rate of leakage air flow through the building envelope at a given reference pressure (usually 50 pascals "Pascal (unit)"), divided by:.
The effective leakage area (ELA) at a given reference pressure is also a common metric used to characterize the tightness of the enclosure. It represents the area of a perfect orifice that would produce the same air flow rate as that passing through the building envelope at the reference pressure. To allow comparisons between buildings, the ELA can be divided by the envelope or floor area, or can be used to derive the normalized leakage area (NL).[13].