Air dispersion superiority with linear vents
Besides condensation, fabric can outperform metal diffusers in air dispersion performance. A fabric duct’s construction is unique in that it incorporates a variety of factory-designed, integrated vents (or nozzles) that span the duct length in a linear fashion and are specified at no extra charge. The linear design allows for a uniform dispersion of the mechanical system’s dry, conditioned air across windows, ceilings, and walls to prevent condensation.
In contrast, natatorium metal duct is typically round spiral duct with registers installed at intervals along the duct. Not only do those metal registers distribute uneven air streams that are stronger near each register and weaker between them, but the subsequent drafts may cause a chilling effect on swimmers. Metal duct does have linear dispersion capabilities with slot diffusers, but those options are more costly than fabric ducts’ laser-cut linear vents. Metal slot diffusers can be cost-prohibitive because a typical natatorium perimeter ventilation configuration requires multiple linear vents aimed at dedicated targets, such as ceilings, walls, windows, and the pool surface.
Fabric duct is easily manufactured with multiple linear vents and orifice diameters engineered to provide the desired throws specified by the consulting engineer. For example, a duct run with the wall on the right side might have the following linear vent configuration and percentage of distribution dictated by orifice diameter: 10 o’clock for the ceiling (30 per cent); 2 o’clock and 5 o’clock for the upper and lower wall or windows (60 per cent combined), respectively; and the 7:30 mark for the pool surface (10 per cent). Each vent is individually designed to achieve the desired throws necessary. For instance, a maximum velocity of 9.1 metre/minute (30 FPM) is recommended across the pool surface, but vents covering the ceiling may need much higher velocities and longer throws. On-site installation of four linear configurations of corrosion-resistant aluminum slot diffusers which need to be individually balanced will increase project costs. Fabric duct is factory-designed and balanced when it arrives on site.
Fabric duct helps value-engineer a $48 million aquatic centre
Metal is often misconceived as less expensive than fabric. Length for length, metal may indeed be less expensive; however, in the end, the required extras drive up the price. Fabric duct is factory-designed as a complete system with all the extras, such as suspension hardware and dispersion vents. Metal duct is rarely priced to include all the extras, such
as suspension hardware, boots, registers, insulation, and corrosion protection in natatoriums.
Another consideration is fabric duct installs 40 to 70 per cent faster than metal. For example, the recently constructed 8400-m2 (90,000-sf) Aquatic Center at Mylan Park in Morgantown, W.Va., saved upwards of $55,000 because its mechanical contractor, A. Durer Inc. (ADI), Morgantown, value-engineered the ventilation to fabric duct from the originally specified polyvinyl chloride (PVC) coated metal duct. The multi-million dollar facility, which combines a separate competitive swimming/diving pool and community pool under one roof, is one of the most state-of-the-art indoor aquatic facilities in the state (see illustration A).
Fabric duct decreased labour costs and reduced trade stacking, because it was installed 60 per cent faster than metal duct. As a result, it shaved six to eight weeks off the ductwork installation. Further, the ability to fast-track allowed other trades to complete their work sooner than would have been possible. The fabric duct’s single-point anodized aluminum suspension system serving the Olympic-size competition pool and six-lane diving well was installed in just 10 days. Afterward, only five days were needed to hang the 300 m (980 ft) of fabric ductwork, consisting of 2.4 m (8-ft) diameter headers and branches ranging from 1220 to 1420 mm (48 to 56 in.). The 568,000 L (150,000-gal) community pool’s suspension system and 110 m (360 ft) of perimeter air dispersion was installed in less than a week.
The white fabric duct also eliminated additional costs for field-applied anti-corrosion coatings and paint to match the interior white décor scheme.
Fabric duct’s design flexibility helped solve the challenge of fitting the originally specified large diameter spiral ductwork through truss openings to create clean sightlines for spectators. The centre-positioned 2.4-m (8-ft) diameter trunk line runs between the trusses with smaller diameter branches to fit through open web truss members. The result was an esthetically pleasing layout with minimal cost changes.
