Fabric Air Distribution Duct
Pavesi and Associates, Inc. has over 21 years of experience designing Fabric Air Distribution Duct systems for the Industrial, Commercial and Institutional markets throughout the United States, Canada, Mexico and South America.
The air distribution duct fabricated from polyethylene or polyester flame retardant fabric material is an extremely cost effective alternate to metal duct for the transfer and/or diffusion of unheated, heated, cooled, dehumidified and humidified air.
Other names commonly associated with fabric air distribution duct include air sock, fabric air duct, flexible air duct, fabric air diffuser, fabri-jet duct, poly FR tubes and sock duct.
Fabric air distribution ducts are available in 6" - 120" diameters and any length (length determined by fan capacity). A standard duct comes with a full-rounded end cap and a hem at 12:00 o'clock with grommets or snap hooks spaced 6' apart to support the duct.
Fabric air distribution ducts can be unpunched and open both ends (transfer only) or punched with holes on one side, both sides, above horizontal, below horizontal or any combination thereof.
Fabric air distribution ducts can be custom punched to meet the specific needs of the application, i.e. low, medium or high velocity. Permeable polyester FR fabric is available in several porosities for draft free and minimal velocity applications.
Discharge velocity and throw can be varied based on static pressure, hole diameter, hole spacing and the number of holes. Individual duct design will be determined by the specific application. Small diameter holes are used where low velocity and throw are desired. Similarly, large diameter holes are used where high air velocity, throw and air mixing are required. Hole diameter can vary from 1/4" to 6" (or larger) as required.
A fabric air distribution duct system could be one duct or multiple ducts complete with branches, elbows, tees, offsets and/or reductions. Other options include full circumference zippers to facilitate the installation of long ducts and multiple duct systems; zippers in the end cap for clean-out and bleed/diffusion; two-point suspension system with hems at 3:00 and 9:00 o'clock to eliminate/minimize duct droop when the air handler is not operating; and mounting hardware kits.
An extra hem can be affixed at the 6:00 o'clock position to enable the end user to rotate the duct 180° for summer and winter operation - 2:00 and 10:00 o'clock (winter mode) becomes 4:00 and 8:00 o'clock (summer mode) when rotated 180°.
In applications where the end user wants to blow the air up in the winter and down in the summer but doesn't want to rotate the duct 180°, we have the BIFLEX duct. The BIFLEX duct has an internal bladder or baffle (1/2 the duct circumference) sewn into the duct at 3:00 and 9:00 o'clock along the full length and two sets of custom punched air distribution holes - one set above and one set below horizontal. The bladder allows the end user to blow air up in the winter mode and down in the summer mode without rotating the tube.
In the Summer Mode, entering air forces the inner bladder or baffle up against the "outer skin" on the upper half of the fabric duct thereby sealing off the air distribution holes punched above horizontal.
In the Winter Mode, entering air forces the inner bladder or baffle down against the "outer skin" on the bottom half of the fabric duct thereby sealing off the air distribution holes punched below horizontal.
Polyethylene FR material used in most Industrial applications is fabricated from woven HDPE rip stop material, coated for non-permeability and suitable for temperatures up to 150° - 160°F. Polyester FR material is used in many upscale Commercial and higher temperature Industrial applications (up to 350°F). Silicone coated, fiberglass and other materials are available for applications up to 1000°F.
For maximum performance and longevity, air entering the fabric duct should fill the full diameter. A mechanical air straightening apparatus and/or a section of metal duct (discharge extension) is recommended to be installed at the discharge of the supply air source to eliminate System Effect and straighten the air before it enters the duct.
As a rule of thumb, fabric ducts are sized based on an entering air velocity of 2000-2400 FPM for most applications and 1400-1800 FPM for low and medium velocity applications.
In applications where specific ceiling to floor clearances must be maintained and/or where there are impairments at the ceiling that can't be easily relocated, i.e. trusses, equipment, sprinklers, lights, gas lines ... etc., smaller diameter ducts, and/or multiple ducts can be used.
Fabric ducts can also be used to laterally transfer excess heat or cooler air to other areas of a facility and as a summer ventilation system.