Mechanical engineer, Alan Wilson, P.E., principal, at the mechanical/electrical consulting engineering firm, Bechard & Associates, San Diego specified the fabric duct for heating and air conditioning air distribution in the twin 12,400-square foot and 11,000-square-foot gymnasiums. The gyms are the focal point of the new 65,000-square-foot Semper Fit Fieldhouse at the California Marine Corps base, Camp Pendleton, the nation’s largest Marine Corps Base.

Even though Wilson specified fabric duct to fulfill the request for value engineering the project, government engineers who were previously unfamiliar with the technology accepted the specification, but contingent on smoke test results. “I think everybody (contractors, Marine engineers, consulting engineers, and architects attending the test) were really quite surprised at the smoke test result,” said Philip Lucas, T.B.E., vice president of San Diego Air Balance, Escondido, CA, which performed the smoke test. “Not only did the air drop down to the government’s required six foot level from the 50-foot ceiling, but the airflow was more evenly dispersed than metal duct and registers. The airflow in the duct seemed to be engineered perfectly,” said Lucas, who has performed a couple of dozen smoke tests over his 25-year career.

“We’re pleased with the system that was designed and put in place and it’s been working fine for almost a year without problem,” added Bill Shatzer, project engineer, Camp Pendleton, U.S. Marine Corps.

Wilson, who had specified fabric duct in previous projects, used a straightforward design of a running one 32-inch-diameter, 90-foot-long run parallel to the ceiling trusses for both the 11,000-square-foot and the 12,400-square-foot gyms. Manufactured by DuctSox™Corp., Dubuque, Iowa, the “Marine blue” TufTex fabric duct was factory engineered with 2.5” diameter High-Throw Series orifices at 4 o’clock and 8 o’clock. The orifice size was determined to yield adequate throw while the quantity of orifices was calculated to provide equal pressure and air dispersion along the entire length.

Supplying the fabric duct is a sheet metal plenum fabricated by the project’s mechanical contractor, A.O. Reed & Co., San Diego. The plenum has a series of volume dampers that distribute the 34,000-cfm and 30,000-cfm of air of each gym equally into each fabric duct run.

Wilson saved the Marines approximately 15-percent in labor and materials versus specifying spiral metal duct and registers. Because it is 90-percent lighter than metal duct, fabric duct also saved the project in construction material costs because the tube joist/metal deck roof of the concrete block-style building didn’t have as large of a weight load to support.

While the Marines’ prescriptive approach to a gymnasium was a heat-vent system with unit heaters and large wall louvers for exhaust and outside air, Wilson and A.O Reed’s approach offered the much needed benefit of air conditioning while only raising the project cost 3 to 5 percent. “The exhaust louvers required for the proposed system were quite costly. The design-build team proposed the upgraded air conditioning system with fabric supply distribution ductwork. This creative alternative provided them with air conditioning and improved indoor air quality with only a slighter higher cost,” said Wilson.

While the smoke test was the proof the Marine engineers needed, both Wilson and A. O. Reed assumed risk by installing the system before approval. “We were very confident of the system’s performance because of our past experiences with fabric duct. DuctSox’s product literature and application guidelines were a helpful tool during the design phase. Working with A.O. Reed assured that the installation would be faultless,” Wilson said.