The perpetual flexing of the roof of the nation's largest column-less exhibit hall presented hvac designers with a nearly impossible challenge.

Claimed to be the first fabric hvac duct for a U.S. expo hall is DuctSox at Pittsburgh's new column-less David Lawrence Convention Center.
Pittsburgh's great tradition of suspension bridges is paid homage by internationally known architect Rafael Vinoly's sloping suspended cable roof design for the Pittsburgh Sports and Exposition Authority's (SEA) new $354 million David L. Lawrence Convention Center.

While the soaring stainless steel and glass crown made it possible for Rafael Vinoly Architects PC, and architectural project partner HNTB, to design the nation's largest column-less exhibit hall, the roof's perpetual flexing presented hvac designers with a nearly impossible challenge of effectively distributing heating and cooling throughout the 250,000-sq.-ft. space.

Because snow, rain and wind loads can flex the roof as much as three feet, ceiling-hung metal hvac ducts would have been impossible because of their rigidity. Instead, the project specified polyester-based fabric air dispersion, manufactured by DuctSox, Dubuque, Iowa, which not only floats with the roof's random flexing, but also saves the project an estimated $250,000 versus other duct materials, according to John Patten II, CIPE, principal at the project's mechanical/electrical/plumbing consulting engineering firm, Burt Hill Kosar Rittelmann Associates, Butler, Pa. "We could have used double walled spiral metal duct," recalls Patten, "however that would have necessitated hundreds of expansion joints (to accommodate the flexing) which would have been costly and much less attractive than the sloped, continuous runs of DuctSox we have now."

The fact that the David L. Lawrence Convention Center is the first major convention facility to ever use fabric duct is a milestone for the category. Fabric duct has been popular in Europe for more than 30 years and is now gaining momentum in the U.S. due to its superior air dispersion qualities, light weight, easy cleaning characteristics, ease of installation, and other advantages. When Phase III is completed next year, the total exhibit space will have two dozen 115-foot lengths of 32-in. dia., air permeable DuraTex High-Throw DuctSox. Each duct run, which is supplied by a series of Trane Co., Tyler, Texas, air handlers, begins and ends at approximately 24 feet high and then bows to a 46-ft. elevation in the middle while emulating the contoured slope of the roof.

Mechanical contractor Limbach Co. installed the DuctSox in pairs that run through a series of specially fabricated metal hoop hangers that not only hold light trusses between each duct pair to cut lighting glare, but also eliminate any fabric deflation during off-peak operation. Burt Hill specified a translucent duct fabric that would help disseminate light.

Instead of registers, the DuraTex fabric has factory-engineered permeability to distribute up to 15% of the airflow through the material. The remaining 85% of the air distribution is through hundreds of CAD-engineered perforations that run the entire lengths of the convention center's ductwork.