FLIR i3 User Manual page 90

16 – Introduction to building thermography
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Figure 16.5 Distribution of pressures on a building with two openings and where the external temperature
is lower than the internal temperature. 1: Neutral zone; 2: Positive pressure; 3: Negative pressure;
h: Distance from the neutral zone in meters.
The position of the neutral zone may vary, depending on any leaks in the building. If
the leaks are evenly distributed vertically, this zone will be about halfway up the
building. If more of the leaks are in the lower part of the building, the neutral zone will
move downwards. If more of the leaks are in the upper part, it will move upwards.
Where a chimney opens above the roof, this has a considerable effect on the position
of the neutral zone, and the result may be a negative pressure throughout the building.
This situation most commonly occurs in small buildings.
In a larger building, such as a tall industrial building, with leaks at doors and any
windows in the lower part of the building, the neutral zone is about one-third of the
way up the building.
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Publ. No. T559580 Rev. a486 – ENGLISH (EN) – November 17, 2010