Machine Design

Air doors not just hot air, CFD shows

Air curtains or doors are actually streams of air blowing down from an overhead unit in an open doorway.

Paul Dvorak

They keep out winter gusts and summer heat. To better understand how air doors operate, Berner International Corp. Project Engineer Phil Thomas began simulating his design in CFdesign, fluid-flow software from Blue Ridge Numerics.

Air doors still get an occasional knock because some work and some don't. But Thomas' simulations show that properly designed air doors can effectively separate a 15-mph winter wind from a warm room. "An efficient air door has three qualities: velocity, mass, and uniformity. Skimp on any of these and the door does not work," says Thomas. If a doorway is open to traffic several hours a day, he says, the air curtain pays for itself.

At Berner, CFdesign helps design plenums, determine how to space fans, and find their best angles — all without building prototypes. And architects find the analyses particularly helpful because seeing air flows helps them diagnose HVAC problems.

Thomas also found the software worked well for presentations. "People who watch presentations made with the software ask a lot of good questions, which means they understand what they are seeing," he says.

The cross section of a CFdesign simulation shows a hall (left) leading into a room. A 4-mph breeze blows down the hall. The air door (center top) separates the hall and room. Berner claims its air doors can stop 30-mpg gusts and work in openings up to 30-ft high.

A simulation at Berner of a competing air door shows outside air pushing past the air door with only a 2-mph breeze. Isosurfaces represent the same velocity.

A thermal view of a 2-mph breeze shows it easily blows past a competitive air door on a cold day. The colors show temperatures. Warm (red) air is blowing into the room from an overhead duct.

Berner International Corp., (724) 658-3551,
Blue Ridge Numerics Inc.,

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