Textile HVAC duct might be manufactured to ship airflow efficiency equal to its metal duct counterpart, however with higher outcomes.
Fabric duct is typically utilized in long aesthetic runs with few offsetting variances. However, few engineers and contractors are conscious that elbows, Ts, Ys, reducers and any unconventional radius or angle wanted for a challenge may be custom-manufactured in textile equally as efficient and value-effective as metallic. Literally, almost anything that can be fabricated from spherical metallic duct can be made in fabric duct.
For example, the new $133 million, 275,000-square-foot Irving Convention Center in Irving, Texas, incorporates fabric ductwork with more fittings, offsets and different variances than most different services within the U.S. The exposition space features more than 1,200 linear toes of permeated textile duct with excessive-throw orifices to achieve the ground space 50 ft under.
It was a difficult design-build venture for the mechanical contractor Dynaten of Fort Value, Texas, and undertaking supervisor Chuck Gamble. Utility piping, electrical and structural steel presented myriad obstructions to circumvent. Nevertheless Dynaten didn’t hesitate specifying with textile duct fitting diameters of twenty-two, 40, forty four, 64 and 76 inches. Additional challenges arose when Dynaten had to return to the CAD 3-D drawing board a number of occasions as the mission made several building structural changes during building. Thus, the venture totaled greater than 24 elbows of various diameters, 14 offsets and a myriad of textile-to-textile adaptors to reroute ductwork whereas minimizing static strain will increase.
Incidentally, friction loss in textile is considerably less at 0.01 versus metal’s zero.1 water gain per a hundred ft. In lots of projects, this permits using smaller fan motor horsepower in equipment specifications, which in turn potentially reduces operational prices and expensive sizes. Nonetheless, when a project’s unique steel duct specification is transformed to fabric duct for causes resembling worth engineering, tools dimension doesn’t usually change. Tools downsizing is just possible when textile duct is specified from the beginning stages of design. That’s why engineers ought to at all times consult with a textile duct producer from a project’s starting design levels.
The ICC fitting radiuses went properly beyond normal ninety and 45 degrees. To keep away from structural elements, some elbows required 5-degree, 15-diploma, forty three-diploma and another unconventional angles.
Like metal duct, fabric duct begins off as a flat sample and is available in a five-gore elbow design as an alternative of a mitered elbow, the latter which induces more static pressure resulting in a decreased effectivity. Not all fabric duct manufacturers offer a 5-gore elbow.
From Dynaten’s design, the specified textile porosity and vents were chosen after assuring the airflow would be sufficient for the applying. Factory engineers oversee the design course of, nonetheless the mission mechanical engineer chooses diameters as a place to begin and OKs parameters resembling inlet velocities, vent placement, complete cubic feet per minute of the run, variety of vents, duct sizes and other specifications.
At ICC, the textile duct was designed for prime throws of about 50 toes. The excessive throws required onerous rubber grommets in 2- and three-inch diameters with various spacing depending on every specific area’s airflow requirements, which resulted in dozens of orifices per run. Some engineers are skeptical about high-throw textile duct versus standard metallic duct/register systems, but fabric has an equal capability to throw up to 150 ft with satisfactory static pressures.
Moreover, the tightly spaced orifices supply a extra evenly distributed airflow than metallic registers every 10 to 20 toes.
The factory’s CAD system digitally directs the slicing technique of the material to precise dimensions. It’s then sewn collectively along with any specified accessories akin to cable suspension attachments or zippers to adjoin sections.
Textile fittings can emulate almost any metallic fitting configuration. The greatest distinction between steel and textile manufacturers is the previous welds and the latter sews utilizing manually-operated industrial sewing tools. Every textile duct element and fitting is bagged separately with figuring out numbers and diagrams that describe its exact position in the general air-distribution network. Because of the project’s complexity, Gamble first laid out the ICC model on Dynaten’s warehouse floor earlier than set up.
While textile and metal manufacturers have equal design capabilities, textile duct gives many extra benefits. For example, installation labor costs are sometimes 20 p.c to 60 percent less than spiral metal duct in most tasks. On the ICC for instance, hanging the 76-inch-diameter trunk strains required about the identical quantity of installation time because the project’s 22-inch branches. That advantage would positively not hold true for hanging comparable sizes of steel. Thus, the hours required to install the ICC’s textile duct was estimated as 50 % less than metal, leading to tens of thousands of dollars in savings for Texas taxpayers.
Each 22-, forty- and forty four-inch-diameter duct run on the ICC is suspended by only two wall anchors that assist a horizontal suspension cable. Metallic duct, which is 90 percent heavier than textile duct, would have required a whole lot of ceiling anchors and vertical threaded rod ties.
The bigger sixty four- and 76-inch-diameter textile duct sizes required triple horizontal suspension cables per run. Metal ductwork would have required dozens extra ceiling anchors for vertical supports.
The lightness of textile duct also promotes ease of installation and particularly increases job safety. Hanging a limp, 76-inch-diameter textile elbow onto a suspension cable is comparable to threading a shower curtain by means of a rod. Conversely, hanging a steel elbow requires significantly more manpower, heavier tools and rigging maneuverability.
One other advantage is the ICC textile ductwork minimizes condensation, which is a possible drawback in Dallashot and humid summers. The fabric duct has a built-in anti-microbial agent to forestall biological growths from harboring contained in the duct runs and fittings. Conversely, single-wall metal sometimes collects condensation that drops on occupants under. Insulated duct minimizes condensation on the exterior surfaces but is more expensive. The insulation can also be doubtless to collect dust, mold, mildew and different contaminants.
Insulation in steel duct can also be designed to cut back heat gain.
Phil Sloan is the inside sales supervisor/engineer at DuctSox Corp. in Peosta, Iowa, he oversees all textile HVAC duct tasks from design by manufacturing. Sloan holds a bachelor of science degree in engineering from Loras School in Dubuque, Iowa.