| Instead of the original specification of 80-inch-diameter metal duct—which also would have impeded forklift mobility under the 26 to 35-foot-high sloped roof—the consortium saved Star Precision approximately $500,000 mostly in ductwork installation labor, duct materials, and less expensive HVAC support equipment by using fabric duct manufactured by DuctSox, Dubuque, IA.
Besides labor and material, additional cost savings are realized because the fabric duct is 90-percent lighter than its metal counterpart. The industrial grade TufTex™ white fabric reduced the need for secondary framing to accommodate the heavier roof load anticipated with metal duct, according to Bakel.
Aside from cost however, the fabric lends an aesthetic appearance as well as better air dispersion than metal duct. Each pair of duct runs have factory-engineered linear mesh vents installed lengthwise at 6, 7 and 8-o’clock and 4, 5, and 6 o’clock to cover every inch of the factory floor.
“With any type of ductwork we were concerned with uneven air dispersion around our manufacturing and fabricating equipment because temperature changes can change tolerances and affect quality control,” said Hayes, who added that temperature variances produced unpredictable machinery tolerances at Star Precision’s former location.
Adds Bakel: “If we put in the originally specified 32 registers with the metal duct, which would have been approximately 10,000 cfm/register which is pretty drafty—it could blow your hat off.”
Machine tolerances, plus worker comfort, were top considerations because Star Precision’s former plant had little air flow from eight ductless evaporative coolers that simply blew conditioned air through the back wall. “Workers were either too cool or too hot because the conditioned air was either drafty or stratified from a poor exhaust design,” added Hayes.
AC&H’s design/build concept keeps the plant at a cool 78°F even though heat generation surpasses 120°F from each of Star Precision’s 30 metal machines consisting of brakes, punch presses, laser cutters, water jet cutters, and other machinery.
The main production floor’s HVAC design uses a myriad of strategically placed ceiling and wall fans to eliminate collected hot air at the roof level and exhaust enough air to produce a positive building pressure. Ceiling exhausts are thermostatically controlled to remove heat, however the wall fans have sheet metal duct drops 18-inches off the floor to eliminate air stratification and pull air from the 20-foot-high fabric duct. “The abandoned original design called for all roof-mounted exhaust fans that when combined with the weight of the sheet metal duct might have surpassed the ceiling load bearing specification,” added Roger Bakel, AC/H Professional’s head estimator, who distributed the fan weight more evenly with wall installations.
“Everybody that looks at what we’ve done with this HVAC design just can’t believe the indoor air quality we’ve achieved, mainly because they’ve never heard of fabric duct,” said Roger Bakel. This is really a perfect product for gymnasiums, indoor pools, warehouses and industrial plants like this one.” |