by Nick Kaufmann, Director of Manufacturing and Engineering — Fabric ductwork innovation has exploded the last decade to offer air dispersion solutions to today’s facility HVAC air comfort and efficiency challenges.
Three decades ago DuctSox fabric duct systems began rather meagerly with straight runs from HVAC air handlers in industrial applications, such as food processing and warehousing.
In contrast, today’s new DuctSox products have become strategic product specifications both in new construction and retrofit applications in industries such as retail stores, data centers, offices with underfloor air distribution (UFAD), athletic venues, restaurants, laboratories, agricultural growing rooms and other facilities.
Solving Under Floor Air Distribution Temperature Challenges
The trend in office ventilation the last decade has been toward UFAD where cabling, piping, utilities and HVAC ventilation is concealed below raised floors, but also easily accessed through floor panels for reconfiguration, additions or retrofits. DuctSox has helped improve this category in terms of temperature control and fan energy conservation with its UnderFloorSox (UFSox) innovation.
The typical 12 to 18-inch-high raised floor creates a convenient plenum to distribute air. Conditioned air typically pressurizes the plenum from building supply trunk line ductwork or variable air volume (VAV) boxes. The pressurized plenum forces conditioned air up into the occupied space through adjustable floor diffusers that can be incorporated into any 2 x 2-foot floor panel. Office workers can adjust the floor diffuser closest to their work space for personal temperature control.
UFAD’s greatest challenge is thermal decay at the perimeter, especially near solar gain sources, such as windows or exterior walls. Getting air to the perimeter is sometimes a pressurization challenge that facility managers try to alleviate by raising the space temperature, which in turn, makes inner spaces too cold near the building core. Increasing fan speeds on variable speed designs is also very inefficient. Temperature swings from the perimeter to the inner areas near the building core can vary as much as 10-degrees when UFAD doesn’t operate as designed.
UFSox, which is typically 12 to18-inch-diameter fabric duct lengths factory-modeled and designed for UFAD systems, connect to the plenum’s metal supply ductwork to deliver air where it’s most needed (see Illustration 1).
In perimeter thermal decay incidences, for example, air can be dispersed directly near floor diffusers where there are employee air comfort complaints. The flexible UFSox can easily be reconfigured and routed around the inherent myriad of cabling, piping, vertical floor supports and other concealed obstacles commonly found in UFAD systems.
Eliminating Fabric Duct Roll-Out Noise, Wrinkling and Sagging
Fabric duct’s advantages over metal duct/register systems:
- 90-percent lighter than metal, which can result in lighter weight structural steel in facilities for an overall building construction savings. Light weight also promotes more employee safety especially with high ceilings.• Linear vent air dispersion distributes air more evenly than metal register/diffusers every five to 10 feet for better energy efficiently. Linear air dispersion (and porosity, if used) provides better air comfort with less drafts.
- 40 to 60-percent faster and less expensive to install in labor.
- More streamlined and aesthetic than metal.
- Easily cleaned with quick disassembly and commercial laundering.
- Many times less expensive than metal in material costs.
- Available in multiple colors and doesn’t require painting or coatings.
- Easy to work around existing obstacles in remodeling applications.
- Can’t get dented from errant objects in athletic facilities.
Furthermore, fabric duct’s superior airflow makes it more energy efficient than metal duct/register systems, according to a 10-month-long study performed by the Iowa State University’s Mechanical Engineering Dept. Thermal Comparison Between Ceiling Diffusers and Fabric Ductwork Diffusers for Green Buildings proved fabric duct has a 24.5-percent efficiency differential, because it heats rooms faster and more uniformly to satisfy temperature set points versus metal duct/diffusers. This results in reduced mechanical equipment runtime, thus saving energy in the process. The study is available free at www.ductsox.com/IA-STATE-Thermal-Comparison.
Fabric duct has gained significant market share in the open architectural ceiling market the last 10 years due to its many advantages over metal duct. Fabric duct installs faster, is more energy-efficient (see a thermal comparison), and disperses air more evenly with linear vents, while also offering improvements in aesthetics, colors and streamlined design over spiral round metal duct and registers, the latter which tend to create drafts.
Fabric duct’s only challenge–a sagging or deflated appearance during air handler idle periods–has been remedied with SkeleCore, DuctSox’s innovative cylindrical in-duct tensioning systems for new construction or retrofits.
Instead of a deflated appearance, SkeleCore systems give fabric duct an inflated appearance free of wrinkling, sagging and roll-out popping sounds regardless of air handler operation. It also significantly increases the life of the system, whereas DuctSox offers up to a 20-year warranty
The SkeleCore product line comes in a good, better, best approach of support hoops, tensioning baskets and premium cylindrical tensioning frameworks.
The “good” approach or the SkeleCore Internal Hoop System (IHS) incorporates internal 360-degree metal hoops every five feet that maintain duct roundness. The hoops, which are supported by vertical cables tied into a horizontal cable suspension or U-track run, hold the fabric ductwork open and taut, regardless of air handler run times.
The “better” or SkeleCore Pull-Tight approach is a combination of tensioning baskets and internal hoops. It’s suspended from either a cable or track suspension system. The tensioning locks, which connect the tensioning baskets to the suspension system, tighten and lock the fabric externally into a taut, smooth appearance.
The “best” or premium method is the SkeleCore Full Tensioning System (FTS), which are 360-degree cylindrical supports attached to a central skeletal spine with a tensioning ratchet device. Instead of just internal hoops, the six-foot-long, tensioning spine’s adjustment nut is ratcheted during on-site installation to spread the front and back support hoops apart, which holds the material taut. It is the most aesthetic method, because it’s nearly a near guarantee from wrinkling and sagging associated with fabric duct systems without in-duct tensioning systems (see Illustration 2).
This method also includes large 50 to 84-inch-diameters to accommodate huge spaces such as arenas.
Cooling Data Center Equipment Energy-Efficiently
The most creative challenges facing data center HVAC today are keeping electronic equipment cool and doing it efficiently. Cooling is not the problem, as engineers can specify as many tons of computer room air conditioning (CRAC) as needed. The challenge lies in dispersing the cooling effectively and efficiently to equipment rack areas critical in preventing overheating failures.
Conventional overhead metal ductwork tends to dump air through registers unevenly, poorly directed or with too much velocity. Excessive velocity causes turbulence that can limit the equipment’s internal fans to draw air in where it’s needed. It can also disrupt exhaust out the back of equipment or cause inefficient turbulence to the return air back to CRACs.
To solve these challenges, DuctSox engineering designed DataSox, a round, overhead and porous fabric HVAC duct system that distributes large amounts of air down into data center cold aisles, but with low 400-FPM velocities that don’t upset critical equipment intake and exhaust or room return air containment balances (see Illustration 3).
It also offers the flexibility of directional spot cooling capabilities with adjustable nozzles for high wattage servers. The nozzles, combined with an internal duct baffle system, allow for onsite testing and air balancing for optimum performance not previously available to the data center industry.
DataSox outperforms conventional data center air distribution methods. Its factory-engineering offers displacement delivery that doesn’t entrain warm air from the hot aisle, resulting in a 3°F to 5°F lower cold aisle temperature, but with up to a 20 to 40-percent less CRAC flow rates, especially when complemented with variable frequency drive (VFD) equipment. Using DataSox helps achieve lower power usage effectiveness (PUE) levels, which makes it a perfect sustainability product for green construction projects.
DataSox is a combination of three DuctSox specialty products:
- Stat-X™ occupies the top portion of the round duct. The white permeable specialty fabric has built-in anti-static qualities from its electro static dissipative (ESD) yarn that is specifically designed for electric-sensitive environments such as data centers. It also disperses a small 2.5-CFM/ft2 of airflow which makes up about 1-percent of the DataSox’s total porosity.
- Custom Porosity Fabric occupies the bottom portion of the round duct to evenly disperse a large, volume of air downward toward equipment rack facades, but without drafts. Each system has a specialized custom porosity volume that allows the air to be distributed in a displacement ventilation manner.
- Adjustable Nozzles positioned in rows along the duct’s length at the optimum angles. These allow for volume when pin pointing at higher wattage servers. The 360-degree rotatable hemispherical diffusers secured inside a two-inch-diameter (33-CFM, 1/2-inch w.g.) or three-inch-diameter (83-CFM, 1/2-inch w.g.) grommet are designed to snap into the laser-cut orifices. The matching white hemispheres can rotate into 10 different notched airflow angle settings including up, down, right or left, as well as completely open or closed. The nozzles also have an anti-condensation design to eliminate concerns of moisture formation on the material.
The fabric duct industry continues to innovate. Critical environments such as laboratories or commercial kitchens are now employing special fabric HVAC ventilation diffusion that makes them more efficient and effective. Furthermore, the world’s first fabric duct sound attenuator was recently introduced by DuctSox to minimize HVAC mechanical equipment noise reverberation through ductwork in sound sensitive environments, such as offices and schools (see Illustration 4).
The future looks bright for fabric duct as it steadily gains market share from metal duct in open architectural ceiling designs.
About DuctSox and the Author
Nick Kaufmann, LEED® AP, is director of manufacturing and engineering for DuctSox Corp., (www.ductsox.com), a Peosta, Iowa-based manufacturer of fabric ductwork/accessories that markets its products globally through HVAC/R manufacturer’s representatives. Kaufmann is a 21-year veteran of the HVAC/R industry. He can be reached at email@example.com or 1-866-DUCTSOX.