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Building air leakage & energy efficiency
Air leakage is the unwanted movement of
air in to and out of a building envelope or component
due to the imperfections in the construction. Causing
cold external air to move into the building, and warm
internal air to move out of the building.
It is often hard to envisage the cumulative size of the
air leakage, but by calculation from air leakage test
results it can be found to be in square metres. Often
there are hundreds of small holes/faults in the
construction that are generally ignored - as not being a
problem, but they are.
The main reasons for measuring air
leakage of buildings:
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To identify ways of reducing heat
loss: The air leakage component of ventilation,
usually referred to as infiltration, can be
significant. Indeed, some buildings are ventilated
just by infiltration, with no designed ventilation
at all. Because infiltration is uncontrollable, the
overall ventilation rate can be excessive in
comparison with the fresh air needs of the
occupants.
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To size heating, ventilation and
air-conditioning (HVAC) systems accurately: In some
cases, the air leakage of a building may be so great
that the system cannot provide comfort during
extremes of weather conditions.
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To avoid draughts: Air leakage can
give rise to localised draught discomfort, for
example people near poorly sealed windows.
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To control ventilation: Excessive
air leakage makes it difficult to control
ventilation systems. For example, in naturally
ventilated buildings with trickle ventilators,
excessive air leakage detracts from their
performance. Problems also arise with poor indoor
air quality due to the ingress of fumes, dust, etc.,
where air leakage can provide an unplanned path for
polluted air entering the building.
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To reduce noise transfer through
leakage paths.
Air leakage can never be considered as
acceptable natural ventilation as it cannot be
controlled or filtered, and will not provide adequate or
evenly distributed ventilation. Air leakage is generally
at its most severe during the colder, windier, winter
months and is least during the warmer, summer months.
This is usually the exact opposite of the requirements
for ventilation within a building. Ventilation systems
should be designed based on the assumption that the
building envelope is relatively airtight.
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What is Building Air Leakage &
What is the Impact?