San Francisco Restaurant Solves Cooking Hood Draft Challenges with Cloth HVAC Diffuser Retrofit

Bridges Restaurant & Bar, Danville, California, was facing seemingly intractable performance problems with its kitchen ventilation system and was willing to spend more than $20,000 on a new rooftop fresh air system.

Instead of reaching outside through the dual exhaust hood, smoke and food odors invaded portions of the 300-square-foot dining area, leading to complaints from guests sitting at tables near the kitchen.

The 24-year-old independent Bridges is best known in the San Francisco area for its casually elegant restaurants and as a famous setting for actor Robin Williams' comedic multiple costume changes in the Hollywood film “Mrs. Doubtfire.” According to Kevin Gin, executive chef and member of the restaurant's investor consortium, due to its upscale image and popularity, the annoying cooking smells in the dining area were detrimental to the business and detracted from the overall guest experience.

Additionally, drafts from the existing fresh air HVAC system sucked in smoke and grease that should have been contained in the hood and deposited it on the diffuser, walls, ceilings and other kitchen surfaces, resulting in an annual maintenance expense of over $1,000 US dollars required and cleaning supplies.

In addition to odor intrusion and maintenance costs, air conditioning drafts over the food preparation area resulted in prepared hot entrees being cooled prematurely, while employees in other kitchen areas were uncomfortably hot.

Find a cost-effective solution
A major HVAC retrofit expense seemed imminent until an arranged meeting between Gin and an HVAC ventilation product manager who was attending a dinner hosted by Bridges to mark the 25th anniversary of the nearby Food Service Technology Center (FSTC), one in San Ramon, California-based commercial foodservice equipment testing laboratory funded by Pacific Gas & Electric. Nick Paschke, product manager for fabric HVAC duct manufacturer DuctSox Corp., Peosta, Iowa, recommended a custom fabric air distribution system designed specifically for kitchens. The ceiling unit distributes the air flow evenly, parallel and in front of the kitchen extractor hood. The fabric diffuser is an easy-to-install replacement for metal air distribution diffusers that often cause kitchen hood overflow.

Instead of replacing the 5,000 cfm fresh air equipment, only the kitchen's single conventional 3' x 3' utility box and four metal diffusers were replaced. The diffusers were located above the food prep line to distribute air throughout the 1,000 square foot kitchen and were replaced with two D-shaped KitchenSox fabric diffusers measuring 8 feet long and 28 inches in diameter. Instead of the metal diffuser's estimated 500 feet per minute airflow, which caused turbulence and interruptions in the range hood's capture, the air is distributed gently and evenly through the fabric throughout the kitchen area at a significantly slower rate of 85 feet per minute . Without the previous high-velocity airflow and resulting turbulence, the dual exhaust range hood now efficiently meets its design standards, trapping smoke, grease particles and cooking odors without causing overflow.

CulinAire Systems, El Dorado Hills, Calif., a foodservice ventilation company specializing in on-demand ventilation controls and engineered kitchen ventilation equipment, fabricated the sheet metal plenum and metal/fabric adapters that feed the 16-foot-long fabric ducts. The fabric duct system and metal accessories were installed by CulinAire overnight without interrupting kitchen operations.

Without the draft, there is no longer any excess air smoke, grease buildup and dirt that the return air system once sucked onto diffusers, kitchen walls, ceilings and cabinets, speeding up daily cleaning and hygiene routines.

Gin also plans to do an annual cleaning, as the fabric diffuser can be disassembled by kitchen staff in minutes and cleaned in the laundry, a process that would take several days with an outside contractor using a metal system.

Green mission accomplished
By improving air distribution and preventing hot air from overflowing from the hood into the kitchen, significant energy savings are achieved, complementing Bridges' green mission, which is strategically marketed to its customers. Gin said it is difficult to accurately determine the energy savings of the new system because FSTC continually uses Bridges as a beta testing site for new technologies. However, Gin estimated that Bridges' recent conservation efforts saved the restaurant more than 20 percent in energy costs and quickly paid off the investment.

For example, FSTC monitors the results of the Bridges Intelli-Hood variable speed controller, manufactured by Melink Corp., Milford, Ohio, which won the prestigious AHR Innovation Award in the ventilation category at the 2012 AHR Expo was awarded in Chicago.

Other eco-friendly devices include:
· A 96% efficient Cyclone Xi water heater from AO Smith, Ashland City, Tennessee;
· Variable temperature control for more efficient operation of walk-in refrigerators from E-Control Systems, Sherman Oaks, California;
· High-temperature/reduced water kitchen and bar dishwashers from Hobart Corp., Troy, Ohio;
· A lighting conversion from standard lamps to compact fluorescent lamps;
· The highest efficiency appliances available today in deep fryers, convection ovens and ice cream makers from Vulcan-Hart Co., Baltimore, Maryland; the Garland Group, Freeland, Pennsylvania; and Manitowoc Ice Inc., Manitowoc, Wis.; respectively.

Bridges' HVAC ventilation challenges were completely solved with fabric diffusers, which cost less than ten percent of the approximately $20,000 for a new fresh air system. In addition, the energy savings and lower maintenance costs allow the air distribution system to pay for itself in less than a year. “This is really a common problem (insufficient draft in the extractor hood). I think a lot of restaurants are suffering from this and don’t realize there’s an easy, cost-effective solution,” Gin said. “We previously thought replacing the HVAC system would improve our kitchen ventilation challenges, but now we realize it likely would not have solved the actual ventilation problem that fabric ducts solved.”