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Variable Speed Comes To The (Kitchen) 'Hood
THE PROBLEM
Most commercial kitchen hoods operate at 100 percent capacity even during
idle periods when ventilation systems can safely be turned down. Because hoods
and
associated exhaust and makeup-air fans are among the largest consumers of
electricity in a commercial kitchen, the annual cost of wasted energy can amount
to thousands
of dollars per hood.
THE SOLUTION
A new technology that reduces ventilation rates during slow periods makes
it possible for restaurants and institutions to significantly reduce
the amount
of wasted energy. Lower fan speeds also means less noise. The concept
calls for control of kitchen ventilation-fan speed based on the amount of heat,
smoke,
and steam released by cooking. Using this approach, Melink Corporation
of Milford, Ohio, has developed a variable-speed kitchen exhaust-control
system
called the
Intelli-Hood that cuts energy consumption by between 40 and 70 percent
compared to traditional hoods (Figure 1).
The Intelli-Hood demand ventilation control (DVC) system incorporates
sensors and a microprocessor into kitchen hoods. The system monitors
cooking activity
and adjusts fan speeds accordingly. With annual fan-energy savings
of $1,500 to $10,000 per hood, plus additional savings of 15 to 40 percent
from reduced
building heating and cooling losses, the Intelli-Hood can pay for itself
in as little as one year. Annual energy savings can top 60,000 kilowatt-hours,
which
translates to reductions of up to roughly 45 tons of carbon dioxide
(CO2) per hood.
FEATURES AND BENEFITS
The Food Service Technology Center, an independent research organization
in San Ramon, California, that tests the efficiencies of a number
of commercial cooking
technologies, tested the Intelli-Hood in 2006. The Center found
that the system provided significant energy and monetary savings at all
of the test
sites. Savings
were also found in field demonstrations at a number of California
colleges, including the University of California (UC) at Santa Barbara,
UC Berkeley,
Butte College,
and Sacramento City College. DVC-equipped hoods are also compact
and easy to install, and they improve the work environment.
By optimizing fan speed, the Intelli-Hood reduces energy consumption
of fans by as much as 70 percent during idle periods. And because
a lot of
air from
the heating and air conditioning systems is sucked up through
kitchen hoods, HVAC
system energy consumption also drops by 20 to 30 percent. This
translates to savings of thousands of dollars per year per hood and
a rapid
payback (Table
1). Also, if the makeup air comes from the dining room, these
systems can further reduce HVAC costs by increasing building circulation
for free cooling
or heating
when outdoor conditions are appropriate.
The Intelli-Hood can also help to ensure optimum indoor air quality
by monitoring the CO2 levels in the make-up air stream. The
exhaust fan
speed can be increased
to 100 percent if the indoor CO2 levels exceed a pre-determined
threshold. For example, in facilities where makeup air comes
from the dining
room, the Intelli-Hood
can detect and moderate CO2 levels in the dining area.
The Intelli-Hood system takes up very little space and can
be unobtrusively incorporated into virtually any standard
commercial kitchen ventilation
hood (Figure 2).
The system can be set up in a few hours by a trained technician
and requires little maintenance.
Exhaust hood fans in commercial kitchens can be quite noisy,
which can lead to miscommunication, a higher risk of
accident, and lower
employee
productivity.
By reducing fan speed, the Intelli-Hood reduces fan noise
by up to 90 percent during idle times - creating a safer
and more
productive
working
environment.
The sensors in the Intelli-Hood system monitor the temperature
of kitchen exhaust air and sound an alarm or shut off
cooking appliances if the
temperature gets
too high.
DVC systems are effective in most commercial or institutional
kitchens, including restaurants, dormitories, hospitals,
hotels, cafeterias,
and banquet facilities.
The system can be incorporated into existing kitchens
or included in new construction. Energy savings depend
on
the fan-motor
loads at full
speed,
the variability of
the kitchen operation, and the number of operating
hours per year. Cost-effectiveness increases proportionally
to the size
of the
ventilation system, number
of operating hours, and airflow rates. The payback
period
is usually between one and four
years in new construction and two and six years for
retrofits. Some utilities offer incentives for restaurants
that
adopt this technology,
further
reducing the payback period.
For more information on this project, visit the California
Energy Commission at www.energy.ca.gov/research/buildings.
More PIER
Technical Briefs
can be found at www.energy.ca.gov/research/techbriefs.html.
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