The differential pressure compensates the differential pressure caused by the natural draught and the wind velocity.
The height of an entrance opening to a shopping-mall is 2.5 m. The depth of the entrance is 1 m. The air flow angle through the entrance is 25 degrees and the air flow per meter width of the opening is 8 m3/s.
The force against natural draught and wind forces can be calculated with (1) as
Δp = 2.2 (8 m3/s)2 sin(25) / 1 (2.5 m)3/4
= 29.9 Pa
The velocity through the inlet can be calculated with (2) as
v = (8 m3/s) / (1 m)
= 8 m/s
The forces we tries to compensate with air curtains constantly varies with outside temperature and wind velocity and some sort of control device modulating the air flow angle and air flow volume may be required.
A modulated control can be achieved with one or more temperature transmitters located as indicated in the figure above.
Air curtain discharge temperatures should be kept within certain limits. For winter conditions
Systems for ventilation and air handling - air change rates, ducts and pressure drops, charts and diagrams and more.
The Beaufort description and observation scale for wind and wind speed.
Dynamic pressure is the kinetic energy per unit volume of a fluid in movement.
Air flow - volume and velocity - due to stack or flue effect caused by indoor hot and outdoor cold temperature difference.
Wind load on surface - Wind load calculator.
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