Fan Hoods, Demand-Side Ventilation Yield Energy Savings for Restaurant
Oct 1, 2008 12:00 PM
In most commercial kitchens, exhaust fans run at a constant speed throughout the day, regardless of load. This not only wastes fan energy, it increases heating and cooling load, as exhausted air must be made up with conditioned fresh air. In Print Works Bistro, part of Proximity Hotel, the first hotel in the world to be certified Platinum under the U.S. Green Building Council's Leadership in Energy and Environmental Design (LEED) Green Building Rating System (Page 20), Intelli-Hood controls from Melink keep energy consumption down by matching fan speed with the amount of smoke/vapor present over the cooktop.
The controls are installed on five hoods manufactured by Captive-Aire — four powered by a single exhaust fan for the main cooking island and a wall-mounted unit and fan servicing a stand-alone baking station.
LOAD MATCHING
With the Intelli-Hood controls, Print Works' exhaust fans operate only when and as much as needed. Cooks simply press the hoods' light and fan switches upon opening the kitchen. A built-in processor signals to variable-speed drives to start the exhaust fans at a preset minimum — between 10 and 50 percent. This speed increases with heat and effluent (smoke and vapor) from the cooktop. (Temperature sensors are installed in the hoods, as are optic sensors that use infrared light to sense effluent.) As smoke clears, the fans automatically slow down, reducing energy use and the need for makeup air.
Beyond turning the system on and off, the cooks need only to worry about wiping clean the optic-sensor lenses once a month and the temperature sensors every quarter. A built-in air-purge system maintains a positive pressure inside of the optic-sensor housings, which effectively keeps smoke and grease from collecting there.
EXTENDING THE SAVINGS
Joe Millikan, PE, LEED AP, president of Superior Mechanical Inc., took the kitchen ventilation savings a step further by installing modulating outdoor-air dampers on the makeup-air unit atop the restaurant. He designed the dampers to operate in response to changes in carbon-dioxide level in the kitchen. So, as exhaust from the kitchen decreases, the outdoor-air dampers modulate closed, decreasing the amount of make-up air in the space, but still maintaining a positive pressure.
With the Intelli-Hood controls and demand-side-ventilation design, the restaurant's energy consumption is half of what it would be otherwise. Furthermore, the inclusion of the Intelli-Hood controls contributed to the earning of LEED's “Innovation in Design” credit.
“This type of design is more effective than an ERV (energy-recovery ventilator) in applications like this, where you have load that goes way up and down,” Millikan said. “To me, this is the single most innovative thing I've seen for a restaurant application. I bet we saved as much with this kitchen ventilation system as we did with the high-efficiency chillers used to cool the hotel and restaurant.”
