Welding Smoke Removed by Air Curtains
“We hit two birds [energy savings and IAQ] with one stone [air curtain technology],” said Michael Coleman, president of Coleman Tool.
The company, a welding, machining, and metal fabrication company that specializes in replacement parts for waste disposal vehicles, wanted air curtains for its new 60,000-square-foot plant, built by design-build company Design 2 Construct (D2C), Jackson, Wis. An in-house mechanical engineering team, which performed much of the building’s mechanical engineering requirements with D2C, specified air curtains for two 16- by 16-foot and one 12- by 12-foot overhead doors.
One CFA and two CFC model air curtains, manufactured by Berner International, New Castle, Pa., retain heat while the doors are open. The building now maintains a 60°F plant wintertime temperature generated purely from the waste heat of its industrial welding process.
This is a sharp contrast to its former building, which didn’t have air curtains; it used supplemental heaters, kept the shipping doors open more frequently, and used exhaust fans to expel welding smoke - and wintertime heat was exhausted too. The new building incurs no supplemental winter heating costs, significantly reduces heat loss during open-door periods, and recirculates heated air through the air curtains, all of which contributes to the company’s ongoing green and environmental-consciousness mission, according to Paul Bugner, head of maintenance.
The air curtains are activated manually or with a limit switch triggered by a door opening. They help maintain the temperature because they eliminate outdoor air infiltration. Air curtain technology draws interior air from the facility and discharges it through field-adjustable (±20°) linear nozzles to produce a nonturbulent airstream that meets the floor approximately at the threshold of the door opening.
Temperature differences and prevailing wind conditions cause the majority of air exchange and resulting minimal energy loss across the opening. An air curtain can contain approximately 70-80 percent of that air and return it to the space. Because the air curtain discharges at velocities generally in the range from 3,000 to 6,500 fpm, the strong air stream shield prevents outside air and insect infiltration.
To continually protect the door opening from these exter- ior forces, Berner factory-engineers these air curtains for size, air volume flow rate, airstream velocity, and discharge nozzle uniformity, which is critical to air curtain performance. These aerodynamic performances are certified by the Air Movement & Control Association (AMCA) International, a not-for-profit association that ensures accuracy in the specification claims of air curtains, fans, blowers, and other air-movement devices.
FILTERING WELDING SMOKEWhile Coleman Tool was racking up impressive energy savings figures with air curtains, the lack of air infiltration and cross-ventilation during the winter had affected IAQ. To control smoke and other airborne contaminants generated by its welding bays and four robotic welding stations, mechanical engineers specified 14 Industrial Maid air filter walls that surround the 15,000-square-foot welding area.
Despite the efficacy of the air cleaners, an estimated 20 percent of the smoke still rose up and out of the welding area, creating a haze throughout the plant. Energy savings were important, but not at the expense of IAQ.
One solution proposed adding tens of thousands of dollars worth of rooftop makeup air equipment to recirculate heated air. Instead, Bugner theorized that the air curtains might serve a dual duty as air cleaners as well as energy savers. The 16-foot height above the doorways was a strategic position to help the air curtains draw in the haze.
Some air curtain manufacturers offer options for conventional filtration add-ons; Bugner felt heavy industrial welding smoke would need a filter holder designed for quick and frequent replacements to keep labor expenses in check. Also, most conventional fiber filters carry a MERV rating of 1 to 6; welding smoke and particulates would need at least a MERV-8 filter - the same rating as the filters used in the welding area air cleaners.
“We designed a filter holder we could manufacture ourselves, that required only 10 minutes or less to replace, was aesthetic, didn’t affect the air curtains’ airflow, and would use inexpensive, off-the-shelf filters,” said Michael Coleman, who has since applied for patents on the filter design, to market it to industrial air curtain users needing heavy-duty filtration.
FINE TUNING THE FILTRATIONBugner experimented with different combinations of inexpensive filter media and filter holder styles to further drive down maintenance costs. Since a 24- by 24-inch filter is a standard off-the-shelf size, the steel filter holder was fabricated to allow eight pleated fiber filters for the two 16-foot-wide air curtains (six for the 12-foot-wide air curtain) to be slid into either end in 10 minutes or less.
The filter holder’s metal fabrication, a Coleman Tool specialty, was designed with light weight and rigidity, but also featured an attractive safety grille that prevented larger items, such as hands or other accidental contacts, from entering the filter portion.
The IAQ results have been significant. The haze is gone, the production floor’s air smells fresher, and the plant’s chronic asthma sufferers notice significant breathing improvements, according to Bugner.
“In our case, we had to have air curtains to save energy, so the fact they also boost IAQ is a bonus that carries virtually little additional cost,” Bugner said. “Anyone who thinks they have a clean environment should put up an air curtain with a filter. They’ll find out the air isn’t as clean as they thought.”
Publication date: 11/15/2010