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Fabric diffusers give commercial kitchens an air makeover.
Restaurants and other commercial food service operations face a common challenge: adequately ventilating cooking areas that can create a lot of grease, heat and smoke. Four-way metal diffusers typically used in commercial kitchens produce high air velocities that flow across the cooking exhaust hood, reducing its ability to capture and vent these cooking byproducts. Without adequate capture, the grease and smoke get blown around, causing indoor air quality and sanitation issues, as well as higher energy and maintenance costs.
This was the issue for the Bridges Restaurant & Bar, San Francisco-area upscale restaurant. According to executive chef and restaurant investor Kevin Gin, cooking odors were wafting into the dining area, affecting patrons, and drafts from the air conditioning supply over the cooking area were prematurely cooling hot entrees. In other areas of the kitchen, employees were uncomfortably hot. In addition, grease was not able to exhaust properly and was depositing on walls, cabinets and appliances, costing time and money to clean and maintain.
Facing an expensive retrofit of the large HVAC system, it was recommended instead to replace the metal diffusers with a custom textile air dispersion system designed specifically for kitchens. The product called KitchenSox™ was developed by DuctSox, a textile HVAC ductwork manufacturer in Peosta, Iowa. KitchenSox is based on a product it had developed for critical laboratory environments where laser equipment and sensitive research projects necessitate controlled airflow and temperature. Product manager Nick Paschke says the company had been researching food service solutions for commercial kitchens based on the success of LabSox, which is used in some of the most sensitive labs in the country and increasingly requested by lab researchers.
“Labs and kitchen markets have similar performance requirements in that they require large volumes of air and desire minimum drafting. They also want easily cleanable products and antimicrobial treatments for sanitation purposes. The flexible fabric also enables easy launder-based cleaning,” says Paschke.
Food service solution
Approximately 40–60 percent of restaurants are not ventilating properly in their kitchens, according to engineers at the Food Service Technology Center (FSTC) in San Ramon, Calif., a commercial food service equipment performance test lab. Prompted by this challenge, FSTC tested different solutions, including KitchenSox, in a typical kitchen ventilation design where a metal diffuser was pushing smoke out from under the kitchen hood. It found that KitchenSox fabric ceiling diffusers mitigated high velocities and turbulence from the HVAC system versus four-way ceiling diffusers that caused well-performing hoods to spill smoke from cooking.
“This is a common problem in the food service industry,” says Rich Swierczyna, FSTC senior engineer and lab manager. [But] “The fabric diffuser slows the airflow down and allows the kitchen hood to exhaust properly.”
The slowdown of the airflow, a result of the fabric’s factory-engineered porosity, is a significant amount—50 to 250 feet/min. (fpm) versus velocities as high as 700 fpm typical of the four-way diffusers, FSTC reported.
At Bridges Restaurant, the installed fabric diffuser evenly disperses air through the fabric at a rate of 85 fpm, compared to the estimated 500 fpm of the previous metal diffuser. The system was easy to install and replaced only the kitchen’s lone conventional three-by-three-foot supply box and four metal diffusers. For Gin, the cost was less than 10 percent of the approximate $20,000 estimated for new make-up air equipment, which may not have even remedied the actual drafting problem: ventilation. “Had they gone in with a system and pushed more air, they would have made a big problem worse,” Paschke says.
Instead, the new air dispersion system improved the exhaust hood’s capture performance and not only eliminated the grease buildup, odors and air temperature problems, but contributed to the kitchen’s overall energy savings and green mission, says Gin. The fabric diffuser is also easy to remove and launder, eliminating the high cost of cleaning and maintaining metal ductwork, and has an antimicrobial agent to enhance sanitation.
While cost savings are significant for retro-fitted systems like the one at Bridges, new construction customers might see neutral cost savings, depending on the configurations they’re considering, according to Paschke. Still, the performance gains in properly dispersing airflow with less draft near the hood has long-term cost-saving implications.
Bridges is now also testing a new micro-perforated fabric by DuctSox called DT200 that promises to reduce maintenance requirements due to larger outlets and less secondary filtration by the fabric in the kitchen. All DuctSox fabrics meet the NFPA 90A building code for fire retardancy for ventilation systems, and additional performance requirements detailed in the newly established UL2518 for textile air-dispersion products.
Breakthroughs
DuctSox is working with a number of restaurant groups and design teams on projects from the local level to national restaurant chains. Typically, capture of airborne cooking byproducts is a function of the hood only. Beyond improved capture, research confirms that proper air-supply dispersion with fabric can maintain capture with less exhaust airflow, reducing the energy required to temper make-up air. These benefits may be applicable to new or existing facilities.
“One of the biggest breakthroughs for us has been within the fabric, as we have worked with suppliers to expand available air permeability,” Paschke says. “When evaluating airflow dispersion through a fabric duct system, a key component of the system is how much airflow passes through the fabric itself.”
For critical environments, such as labs and kitchens, the need to deliver large volumes of air with little or no air movement requires a high porosity material, he explains. Applications that require significant air movement, such as pools and gymnasiums, often require a nonporous material. The ability to offer tighter and looser weaves to meet the porosity needs of different environments has been key for the company’s ability to provide premium performance to customers.
“We used to only be able to move so much airflow through the fabric,” he says. “We’ve developed new weaves so we have much higher air velocity in a controlled manner. We’ve been able to develop these individual diffusers, allowing that product to be used more consistently in labs and kitchens where it is very airflow sensitive.”
These fabrics have also been used in a wide range of applications from displacement air dispersion strategies in commercial spaces, data centers, gun ranges and patient care areas.
Growing in popularity
While DuctSox specialty products group has focused on critical environments, fabric use has been growing in many commercial, and industrial open-ceiling applications. To promote the flexible solution, DuctSox is targeting architects and HVAC engineers with its line of SkeleCore™ internal lightweight metal framework and new Fabric Tensioning System (FTS).
This system maintains an inflated appearance even after the air handling unit is off, which avoids inflating and deflating that can cause fabric fatigue and the disruptive “popping” sound associated with air-handler equipment start-up. It is also more aesthetically appealing and architects are more apt to accept or recommend fabric ductwork with this option. The system is suited for use in dining rooms, too, because it can maintain a perfect, clean shape. “With the FTS system, more architects are moving towards it at a pretty good pace,” says Paschke. “With less inflation impact stress on the fabric system, it also improves the warranty—up to 20 years.”
With improved technology, more facilities are considering fabric, and textile air systems are being applied in thousands of facilities around the world.