Fabric duct helps save high school $380,000, no sweat
KSA's John Kluber, P.E., vice president, and Donald Ware, P.E., chief engineer, searched for a solution to ductwork sweating because of the significant savings at stake. Averaged at $3/cfm, Kluber's low temperature supply strategy reduced air volume by 100,000 cfm and saved $300,000 in equipment costs, not to mention the additional future operating costs of downsized equipment.
Instead of increasing the expense of additional ductwork insulation to prevent sweating, fabric duct was specified since it naturally prevents condensation from developing on the fabric surface. Kluber specified DuctSox fabric ductwork in the 430,000-sq-ft high school's 20,000-sq-ft cafeteria, the 38,000-sq-ft field house, the 13,000-sq-ft natatorium, and 3,800 sq ft of open architecture administrative offices.
According to Bill Beukema, president of construction operations of the project's primary HVAC contractor, Amber Mechanical, using fabric duct also saved an additional $80,000 in labor/installation costs. Because sheet metal material prices have skyrocketed over 40% in the last year vs. fabric costs, Beukema suspects more even money was saved in material costs.
"We saw labor generally cut in half on rooms requiring fabric duct, versus installing metal duct," Beukema said. "If metal duct requires a four-man crew, fabric duct required a two-man crew."
An excitement firstThe cafeteria's expansive 20,000-sq-ft skylight design was possible partly due to the lightness and flexibility of the four 30-in. white fabric duct runs that hang arched and parallel to the room's barrel-shaped ceiling contour. The Kluber design included a 70-in. fabric plenum visibly positioned in a corridor that supplies the four arched ducts over the adjacent cafeteria. This plenum included a custom 3 o'clock and 9 o'clock cable suspension system to accommodate the duct's 45-degree-angle take-off connections that meet the plenum at the typical hanging positions of 10 o'clock and 2 o'clock.
The absence of protruding metal duct registers and the aesthetics of the material also added to the futuristic appearance of the cafeteria design. "I've worked on hundreds of projects," said Kluber, "and this is the first time I've seen architects get excited about ductwork."
Fabric duct also eliminated possible problems with natatorium air distribution as well, such as using expensive aluminum or galvanized metal with special paint, periodic maintenance, insulation, and all the other considerations associated with pool environment ductwork, according to Kluber. The natatorium has a perimeter air distribution system of custom blue, 26-in.-dia. fabric duct supplied by a 33,000-cfm Des Champs Laboratories combination dehumidifier and air-to-air heat exchanger. The duct is hung with an anodized aluminum H-track suspension system with corrosion-proof #316 stainless steel cable drops.
The field house was particularly challenging in air distribution because of its size, high ceiling, and a 20-ft-high, 25-ft-wide running track around its perimeter. Kluber designed a perimeter fabric duct distribution system above the running track's inner edge, however, each 25-ft section has its own custom factory engineered S-vents that vary in placement and diameter as to the needed air throw requirements.
While cost saving was the main impetus for fabric duct, the noticeable difference in airflow quality and aesthetics is an added benefit. "Some people think fabric duct is that shiny, cheap-looking stuff you see in industrial applications, but today's technology gives it a high-end, sophisticated look, and the sleek linear vents provide a much more even airflow than metal duct and registers," said Kluber. Adds architect, Ed Skahan, President, KSA: "Finally, ductwork actually adds aesthetics to a space."
Steaming toward savingsDownsizing air-handling equipment was just one of many strategic equipment cost reductions Kluber exercised through innovative design. For example, he specified two 600-ton steam absorbers by York instead of conventional chillers and saved an additional $114,000 in equipment costs. "Many engineers perceive steam as an antiquated technology, however, steam absorbers are about half the cost of refrigerant chillers," said Kluber. "It's a proven workhorse technology and there's no worry about refrigerants."
All air handlers by Ventrol Air Handling Systems included $125,000 worth of heat-recovery coils by Heat Pipe Technology. Heat recovery equipment will reduce future operational costs. The investment was offset by reducing the necessary boiler requirement by 300 hp, which equals approximately $150,000 resulting in an additional savings of $25,000.
The temperatures are controlled by the BAS, which is an integration of Tridium front end graphics with Honeywell software and hardware from temperature control contractor Control Solutions Inc.
All of these innovative cost reductions were a result of value engineering by city planners to meet the school's strict budget. Typical mechanical costs for schools average $18/sq ft nationally. After value engineering the design, KSA brought the mechanical costs down to $10/sq ft without compromising IAQ and comfort.ES