Fabric duct is one of the fastest-growing segments of the HVAC air-distribution market, representing more than 5 percent of open-architecture-ductwork specification.
Fabric duct is 90-percent lighter and 40- to 60-percent faster to install than metal duct. This, combined with the fact metal prices have increased over the last year, makes fabric duct a value-engineered alternative to metal duct. Additionally, it offers a more streamlined look and is easy to maintain inside and out.
Despite the inroads fabric duct has made, many engineers are unaware of perhaps its greatest attribute: diversity of air dispersion. Fabric duct is capable of more-even air distribution than most other systems, mainly because air can flow through its pores, as well as linear vents running its entire length. This article illustrates five types of air dispersion possible with fabric duct.
LOW THROW WITH POROSITY
Description: Displacement-style diffusion by which air is dispersed through the fabric's porous weave. Porosities range from 6 to 30 cfm per square foot of fabric area at a static pressure of 0.5 in. wg.
Applications: Typically, food processing, although it is being developed for other applications where gentle airflow is preferred. Specialty applications have included duct runs inside of large paint-booth plenums to quiet turbulence.
Comments: Used almost exclusively to distribute cooling. It is not functional for heating because heat would not flow fully into a space from an overhead position.
Description: Non-porous fabric duct with linear array(s) of 1- to 5-in.-diameter orifices and the ability to distribute air up to 90 ft at conventional static pressure.
Applications: High-ceiling areas, such as industrial facilities, athletic buildings, indoor water parks, natatoriums, gymnasiums, and lobbies.
Comments: With factory engineering and 100-percent custom manufacturing, designers can select orifice size, quantity, and orientation (direction) for the precise delivery of air. Throw distances are longer at lower volume than with conventional diffusers, resulting in high entrainment ratios. This produces consistent throws between heating and cooling, as well as uniform temperature distribution.
COMFORT FLOW WITH POROSITY
Description: Combines porosity and linear vents for even air distribution. Linear vents are sized from 5 to 90 cfm per linear foot and can be positioned anywhere on the circumference of a duct.
Applications: Just about any imaginable, particularly open-architecture ceilings.
Comments: Throws range from 4 to 70 ft. As with high-throw ducts, custom design and manufacturing allows designers to select the size, length, quantity, and orientation of vents to optimize airflow performance. The vents disperse low volumes of air at high velocities, ensuring heated or cooled air mixes quickly. Mesh vents may require routine maintenance.
SURFACE MOUNT — DIRECTED FLOW
Description: Air is dispersed from a diffuser via pores and vents. One-, two-, three-, and four-way throws are possible.
Applications: Critical environments, including laboratories and medical facilities.
Comments: Fabric-faced diffusers are available with either a fabric or a metal back pan or can be used with an existing back pan. Supported in a metal frame, the fabric protrudes 6 to 9 in. into an occupied space. Highly porous fabrics and specific vent sizing enable uniform dispersement of airflow.
SURFACE MOUNT — RADIAL FLOW
Description: Air is dispersed evenly though a highly porous fabric panel suspended from the ceiling. The airflow pattern is downward and outward.
Applications: Critical environments, such as laboratories and medical facilities.
Comments: Fabric-faced diffusers are available with either a fabric or a metal back pan or can be used with an existing back pan. Supported in a metal frame, the fabric protrudes 6 to 9 in. into an occupied space.
As director of innovation and new-product development for DuctSox Corp., Nick Paschke specializes in the use of textiles in air-dispersion systems. Listed as inventor on at least seven U.S. and international patents, he holds a bachelor's degree in mechanical engineering from the University of Wisconsin-Platteville.
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