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One of the fastest-growing trends in indoor pool ventilation is fabric air dispersion, or ductwork, as an alternative to conventional metal.

Since the emergence of supply/return ventilation decades ago, metal ductwork particularly the spiral variety with registers every 10 to 15 feet became the indoor pool ventilation standard.

In the last 10 years, however, fabric air dispersion has proven to be a less expensive technology that offers reduced maintenance and a more profitable bottom line.

Fabric has many advantages over metal duct and, in a natatorium?s hostile environment of humidity and pool chemicals, the edge is anti-corrosion. Reasons vary, but metal most likely will corrode despite stellar efforts of galvanizing or using stainless steel, aluminum and chemical coatings. Contrary to popular belief, low-grade stainless steel also will corrode.

High-grade stainless steel will fare better; however, it?s at least twice the cost of fabric duct. Galvanized metal will corrode as well. That?s why engineers specify double-wall models with insulation, which carries a significantly higher materials cost to fabric duct. Galvanized also must have toxic epoxy coatings applied, which doesn?t comply with the 21st century trend of using environmentally friendly materials. Aluminum may not rust, but pitting and nonaesthetic patina spotting is a guarantee.

Metal duct corrodes because of poor water chemistry, insufficient dehumidification, or both. Chloramine buildup due to poor water chemistry attacks metal and other materials. Even the most chemically well-kept pools have chloramine buildup that is subject to periodic air purges.

Mechanical dehumidification is nearly a standard for all new natatoriums today. But hundreds, maybe thousands, of existing facilities still rely on inefficient methods such as supply/exhaust or just conventional air conditioning, which cannot adequately remove high 80 percent to 90 percent relative humidity loads that attack metal.

Unlike metal duct, fabric?s synthetic polyester woven construction isn?t affected by humidity or chemicals, and it doesn?t attract corrosion-causing condensation. An additional guarantee is factory-engineered permeability, which allows approximately 15 percent of the air to flow through the fabric. Thus, condensation or dust can?t settle on the fabric.

Metal and fabric air dispersion systems have optional antimicrobial treatments. That?s extremely important considering current indoor air quality issues.

Fabric air dispersion is almost always a cheaper installation material vs. metal, especially in light of the double-wall construction, insulation and coatings that must be added to fight corrosion.

Installation labor savings typically are 40 percent to 60 percent vs. metal. Reduced labor is one reason fabric duct can earn Leadership in Energy and Environmental Design (LEED) credits on buildings applying for LEED accreditation. Using fewer natural resources (metal) also leads to credits.

There are hidden benefits that won?t appear on a cost analysis sheet. Fabric is 90 percent lighter than its metal duct counterparts, which creates less of a roof load on a facility and reduces the amount of structural steel needed.

Many misconceptions about fabric air dispersion systems exist, such as balancing, air-throw capacity and durability.

Metal duct is balanced through registers with throttled openings and/or diverters within the duct itself. A fabric air dispersion system has a linear diffuser that can?t be adjusted on site, but accessories such as an airflow device are easily zippered into a duct run to balance the air. Also, fabric systems can be factory-engineered to provide airflow differences throughout the duct run.

Metal duct registers throw air farther, but fabric air dispersion systems tests have proven air throws of up to 100 feet, which is considerably higher than most natatorium ceilings.

It varies by manufacturer, but most commercial or premium grade fabric ducts carry 10-year warranties. Hundreds of applications have surpassed 20 years without durability problems.