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The Free area of a Tower louvre should be equal
to or slightly greater than the area of the roof opening. A smaller free area will
increase the resistance, a larger free area gives little advantage.
To minimise rain or snow carry over on intake requires a low jet velocity. The carry over
velocity is approximately 2.25 metres per second.
The Tower Louvre should be selected by use of the formula :-
| Air Volume = Tower Louvre free area |
| Jet Velocity |
The accompanying table shows the free area in square metres
of standard height Tower Louvre for values of length plus width (L & W). However when
used for exhaust the limiting factor is generally resistance to air flow. The graph shows
the relationship between pressure drop and roof opening velocity. |
