Actronaire & 
Powered Aire™ Doors

Introduction | FDA / USDA advice | How air doors work
Air Door features | Aire Door models | Make up air fans
Summary | Free consultation | Wind factors | Negative air pressure

Air curtains vs. wind factors

Wind affects the efficiency of an air curtain.  An air curtain must  generate sufficient velocity and be correctly adjusted to prevent wind from penetrating its seal.

Accurately analyzing the air flow in the vicinity of an air curtain to determine the optimum discharge angle involves some fairly complicated mathematics and physics. But it is possible to take a simplified view of the situation and get a feel for what is going on.

Air curtains designed to exclude insects from doors up to 10 feet high can have maximum velocities at the nozzle in excess of 4000 feet per minute, or over 45 mph. If the nozzle were angled at 90° to the vertical, that is, blowing horizontally instead of straight down, then a 45 mph horizontal wind could be countered.

But only a negligible amount of the air stream’s power would protect levels much below the top of the door, so this would obviously not be an optimum angle. If the nozzle were placed at a 45° angle, half of the 90° angle between the horizontal and vertical plane, about half of the force of the air stream would now oppose external wind at the nozzle. So it would be able to stop about 23 mph winds at the top of the door, and less than that as the air stream gets weaker farther away from the nozzle.

This deterioration in the air velocity over distance must be factored into the equation when deciding at what angle to point the nozzle. The more it is angled towards the horizontal, the farther it must travel before reaching the floor. This means a greater deterioration in airspeed, and also leaves a larger gap between the air stream and the doorway through which external wind could flow.

When these additional factors are taken into account, it turns out that an angle of 20° offers the most efficient distribution of the power of the air curtain. This roughly amounts to splitting the 45° angle that we earlier reasoned could stop a 23 mph wind. Although the actual calculations are quite complex, we can intuitively see that as in the 45° example, we are once again redirecting about half of the horizontal velocity toward the floor. So it should not be surprising that, in actual use, air curtains are capable of stopping about half of 23 mph, or approximately 10-12 mph winds. And this protection extends over the entire surface of the doorway.

It’s probably not a coincidence that average wind speed is in the range between 10 and 12 mph. Wind speeds lower than this cannot penetrate the seal of an air curtain. If the wind is stronger than this, its velocity after penetration will be reduced by about 10 to 12 mph.

Introduction | FDA / USDA advice | How air doors work
Air Door features | Aire Door models | Make up air fans
Summary | Free consultation | Wind factors | Negative air pressure