Fabric Duct Makes Expo Hall’s Roof Design Possible

PITTSBURGH, PA — Pittsburgh’s great tradition of suspension bridges is paid homage by internationally known architect Rafael Vinoly’s sloping suspended cable roof design for the Sports and Exposition Authority’s (SEA’s) new $354 million David L. Lawrence Convention Center.

While the stainless steel and glass crown made it possible for Rafael Vinoly Architects PC (New York, NY) and architectural partner HNTB (Kansas City, MO) to design what is believed to be the nation’s largest column-less exhibit hall, the roof’s perpetual flexing presented HVAC designers with a very difficult challenge of effectively distributing heating and cooling throughout the 250,000-square-foot space.

This photo taken during the construction phase shows the hoops that hold the fabric duct and lighting.

FLEXIBILITY NEEDED

Because snow loads can flex the roof as much as three feet, ceiling-hung metal HVAC air ducts would not have been possible because of their rigidity. Instead, the project specified polyester-based fabric air dispersion, manufactured by DuctSox (Dubuque, IA), which not only floats with the roof’s random flexing, but is also saving the project an estimated $250,000 when compared to other duct materials, according to John L. Patten II, C.I.P.E., 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 duct we have now.”

DuctSox says that the David L. Lawrence Convention Center is the first major U.S. convention facility to use fabric duct, a milestone for the product category, which has been in use for over 30 years in Europe and is now gaining momentum in this country due to its light weight, easy cleaning characteristics, ease of installation, and other advantages, states the company.

When Phase III of the project is completed next year, the total exhibit space will have two-dozen 115-foot lengths of DuctSox’s 32-inch-diameter Dura-Tex High-Throw duct. Each duct run, which is supplied by a series of Trane (Tyler, TX) air handlers, begins and ends at approximately 24 feet high while curving to a 46-foot elevation in the middle, emulating the sloped contour of the roof cables.

Mechanical contractor Limbach Company, Pittsburgh, PA, installed the fabric duct 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 help eliminate any fabric deflation during off-peak operation. Burt Hill Kosar Rittelmann specified a translucent duct fabric that would help disseminate light.

One of the first uses of fabric duct for a U.S. expo hall is at Pittsburgh's new column-less David L. Lawrence Convention Center.

NO REGISTERS REQUIRED

Metal duct also would have required hundreds of registers. Instead of registers, DuctSox CAD-engineered hundreds of patterned perforations that run the entire lengths of the convention center’s ductwork. The perforations range from 1/2- to 1-1/4-inch in diameter, with placements depending upon the height of the duct. At the 46-foot level, the holes are largest and are arranged mostly at the bottom of each duct run to maximize air throw in the draft-free air distribution design.

Disregarding the roof flex, metal duct also would have necessitated heavy insulation to eliminate condensation, especially since the convention center’s air conditioning is delivered at an unconventionally cool 34 degrees F.

Using fabric vs. metal also saved natural resources and provided a more maintenance efficient material, which complements the convention center’s “green” mandate, says DuctSox.

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While the roof’s sloped shape has quickly made it the convention center’s signature feature, Burt Hill Kosar Rittelmann has used the roof to respond to climatic and site ecological concerns by the SEA. The roof shape encourages natural cross ventilation and draws fresh air currents from the nearby Allegheny River. The cooling system also uses the roof to cascade water and reduce the cooling load.

The polyester HVAC duct flexes as the roof bows from snow loads and is said to be reducing project costs by an estimated $250,000 compared to metal duct.

The targeted 34 degree air delivery minimized ductwork and fan capacity, thus reducing energy consumption. An underground aquifer, sometimes referred to as Pittsburgh’s fourth river, is used as a partial condenser medium, reducing the required number of cooling towers on the project.

Chilled water is supplied by third-party source, Noresco (Westborough, MA), which built a $7 million, 6,000-ton chilled water plant for the 1.5 million-square-foot convention center.

The complex’s air quality, temperature, humidity, and other HVAC parameters are monitored and controlled with a building automation system from Alerton Technologies (Redmond, WA).

Phase I (80,000 square feet) of exhibition space opened last February and has already been used for the Home and Garden Show, RV Show, and Auto Show. All 250,000 square feet of exhibition space, plus another 100,000 square feet of meeting rooms and additional basement space — the latter of which includes 24 additional lengths of installed fabric duct — is scheduled for completion next year.

Publication date: 10/21/2002

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