Fabric Ductwork Design and Installation
When the company’s mechanical design team, led by mechanical engineer Ed Briner, took on the new printing plant project, its application of value engineering was able to cut the $1.7-million budget for hvac and plumbing by $300,000. The largest percentage of the savings came from an air distribution strategy specified by Briner and suggested by the project’s mechanical contractor, G.R. Sponaugle & Sons Inc., Harrisburg, PA.
FEWER AIR HANDLERSFor example, instead of using five air-handling units to cut down on long, labor-intensive duct runs, the design team decided to use three large air handlers in the printing production and shipping/receiving areas. This choice didn’t increase air distribution installation costs, however, because polyester fabric duct was substituted for metal duct.
Typically, this type of design for production and warehousing in a 107,000-sq-ft prefabricated metal building that’s slated for light industrial and office use might use between eight to 10 air handlers in the 10,000 cfm range.
Because the fabric duct, made by FabricAir, Inc., Louisville, KY, is estimated to reduce installation costs by up to 60% compared to metal duct, Briner cut the number of air handlers to six larger modular air-handling units from The Trane Company, Tyler, TX. These units still supply the needed total of 60,000 cfm to the production floor, shipping/receiving, and warehousing, but it’s handled with more than 2,000 linear feet of FabricAir’s Perfo® duct, ranging from 30 to 36 in. dia.
Unlike metal duct where the number of supply registers increases cost, each length of the fabric duct has hundreds of pre-engineered holes designed to evenly disperse a draft-free airflow.
“A state-of-the-art hvac system like this could easily cost in the $14 to $16 per square foot range, but we got costs down to the $12 per square foot level,” said Briner.
Sponaugle, a 42-year-old mechanical/electrical contractor and one of Pennsylvania’s largest with 250 employees, is known for supplying progressive solutions on projects. While the GANCOM plant was Gannett Fleming’s first major experience with fabric duct, Sponaugle has suggested and used it on more than 20 projects.
“Sponaugle likes to look at opportunities to create solutions or think outside the box,” said Frank Bonnevier, design/build manager for the contracting firm, “and fabric ductwork is one of the many tools we use to accomplish that.”
When invited to give creative input into the GANCOM design, Bonnevier’s department saw a “Cadillac” ductwork design calling for a high ratio of pounds of metal duct per tons of air conditioning. There were also questions as to whether condensation control by means of insulation in the proposed metal duct was worth the extra material costs since the ductwork was destined for an open environment versus an enclosed ceiling.
FABRIC DUCT SAVESSponaugle’s fabric duct suggestion solved both problems. Fabric duct’s installation and material costs would save 40% to 60% vs. the cost of metal duct. Plus, the fabric duct’s permeable surface prevents condensation.
To supply the duct, Briner specified custom-made air handlers with double walls, two-stage filtration, hot water coil, humidifier, chilled water coil, outside air mixing box, and reheat coil. Each air handler, which is connected to a chilled water loop supplied by a 270-ton Trane chiller, has an economizer cycle and provides a minimum of 15% outside air.
The air handlers and fabric duct are designed to provide a 70Â¿ to 72Â¿F temperature and 40% relative humidity. This indoor air environment is controlled by a BACnet-compliant building automation system from Automated Logic Co., Kennesaw, GA.
“GANCOM’s high-speed printing machines can produce many pages per minute, so if equipment jams because the paper has absorbed too much moisture, or if static electricity from low humidity has caused a problem, then profits are reduced,” Briner said.
The building also uses a space pressurization system to provide ventilation air and maintain indoor air quality, preventing production and storage area vapors and odors from infiltrating the positive-pressured offices.
To supply hot water to the air handlers, Gannett Fleming specified two 1,400-Mbh, flexible water-tube boilers manufactured by Bryan Boilers, Peru, IN. For humidification, the air handlers are supplied by a 1,400-lb/hr packaged steam boiler from Fulton Boiler Works, Pulaski, NY.
For more information on fabric ductwork, visit www.ips-ventilation.com.
Publication date: 09/24/2001