Roof Vent Could Prevent Wind Damage

April 29, 2008 · by DesignIntelligence

A roofer, Virginia Tech faculty members from architecture and engineering, and a graduate student have devised an inexpensive vent that can reduce roof uplift on buildings during high winds, even a hurricane.

A roofer, Virginia Tech faculty members from architecture and engineering, and a graduate student have devised an inexpensive vent that can reduce roof uplift on buildings during high winds, even a hurricane.

New foot-high plastic structures can be seen atop low-sloped roof buildings around Wytheville, Va., where Virginia Tech alumnus Chuck Johnson and his brother, Pat Johnson, operate a roofing business.

Chuck Johnson has also persuaded Travel Centers of America in South Carolina, the Gaston County government complex in North Carolina, a Nestlé’s distribution center in Tel Aviv, and VTKnowledgeWorks in the Virginia Tech Corporate Research Center to use the Venturi Vent Technology (V2T), designed for membrane roofing systems.

The V2T system could revolutionize the way roofing is done, Johnson said. “We are using physics instead of mechanical fasteners or adhesives. The harder the wind blows, the better it works.”

The physics is the Venturi effect – wind forced through an opening speeds up. V2T splits the airflow, speeding up the wind that is forced through the vent (between an upper saucer and a lower dome), which drops the pressure and creates a vacuum. The saucer has a hole on the bottom and three tubes from the saucer to the dome and the underside of the roof membrane. Wind pressure draws air out of the saucer and from under the membrane, pulling the membrane tight against the substrate. “The pressure being created under the membrane is lower than the uplifting pressure of the wind over the roof. The result is a low-pressure condition that prevents the uplift and detachment of the roof membrane,” said Jim Jones, associate professor of architecture at Virginia Tech.

The Johnsons took their idea to Virginia’s Center for Innovative Technology, which referred them to Jones. “Their concept was a tube-shaped vent that would rotate to catch the wind,” Jones said.

Jones saw that keeping up with changing wind direction could be a problem and decided to investigate whether the Venturi concept could be applied to an omni-directional design “so it wouldn’t matter which way the wind came from.”

Jones and graduate student Elizabeth Grant started exploring the geometry of a pyramidal base with an inverted pyramid on top. They presented that idea to Demetri Telionis, the Frank Maher Professor of Engineering Science and Mechanics, an aerodynamics expert, who suggested a similar but rounded shape – the dome and saucer. “Once we decided on the geometry, the fine tuning became Grant’s thesis. She created a model with an adjustable distance between the dome and bowl and began wind-tunnel tests.”

Grant was already an experienced architect and designer whose credentials included affiliation with the Roof Consultants Institute. She made the project her master’s degree research with the other members of the design team as her thesis advisers.

The team designed and built several prototypes and tested them in Virginia Tech’s stability wind tunnel, where winds can reach 150 miles an hour, and in the NASA full-scale wind tunnel at Langley Air Force Base. These tests demonstrated the ability of the vent to generate low pressure that could be used to counter the uplifting forces from high winds.

UL testing is scheduled for June. Meanwhile, hardware and software are being developed to provide real-time monitoring of the vent.

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