Quiet fabric duct saves weight, installation cost for manufacturer
That was the strange hand dealt to consulting engineer Scott Henriques, PE, project manager; and Nora McCawley, senior hvac designer, of Shooshanian Engineering, Boston, and mechanical contractor Victory Heating & Air Conditioning. The project for EMC Corp., a data storage manufacturer, normally would call for ceiling-hung, metal duct for its 50,000-sq.-ft. Milford, Mass. Building that was being converted into a media solutions/software development laboratory with accompanying offices. However, the estimated tens of thousands of dollars in structural support needed for the 18-foot high metal deck roof would have ballooned the budget.
An additional challenge was the mandatory quiet, low decibel air flow stipulated by Mark Flanagan and mark Urbanek, EMC’s project manager and director of construction services, respectively. The techniques involved with the particular software development and application work performed in the lab called for the quietest conditions possible.
Shooshanian’s design solved the load bearing and noise attenuation problems by specifying a fabric duct air distribution system manufactured by FabricAir Inc., Louisville, Ky. Fabric ductwork is 90% lighter and requires considerably less installation labor than metal duct. Fabric duct, which is factory engineered for air flow permeability through the polyester-based material, is the quietest ductwork type in the hvac industry and has been used previously in many recording studios, theaters, and other sound sensitive applications.
Henriques was also asked to adapt 16 used Trane and Carrier air handlers totaling some 180,000 cfm from another EMC property. EMC either had to use this existing equipment or wait 20 to 30 weeks for computer room precision ac. “The air handlers aren’t redundant equipment, but we figured in some over capacity to allow for equipment failure or routine maintenance shutdowns,” Henriques said.
Henriques was able to specify some new equipment, however; namely three new air-cooled 130-ton Carrier chillers, which supply the air handlers.
The six, 100-foot long duct runs begin with a specification of 32 cfm/linear foot and end with 250 cfm/liner foot. The lab’s 30-in. dia system consists of 4,300-sq.-ft. of fabric, giving an average air diffusion velocity of 16 ft/min. “Because of the way the return air was set up, we wanted to dump more air out into the far reaches of the space to provide for good air movement,” said Henriques, who also specified the duct color to match EMC’s corporate blue.
For Victory Heating & Air Conditioning, Bellinham, Mass., everything had to be mounted to the floor, including return lines, plenums, and metal supply ductwork that supplies the fabric duct.