Situated over cook lines, ventilation systems remove cooking heat, effluent and odors.
Type I ventilation systems are grease rated for positioning over grease-producing appliances, including ranges, griddles, fryers and charbroilers. Type II or B units, also called vapor hoods, are designated to handle heat and steam over dishwashers and some oven types.
Size and shape of these units depend on the equipment. Low proximity style hoods sit closer to appliances. Typical uses for these hoods include quick service restaurants with fryer banks or kitchens with low ceilings. The design of island style hoods makes them suitable for placement in the middle of the room.
Filtering options or grease removal devices
depend on the ventilation process, the system’s design and the level of grease extraction necessary. These range from low-tech baffle systems to high-efficiency extractors. Utilizing more filters can help control grease buildup.
Pollution control systems remove smoke, grease and odors before these reach the airstream. The two types include a filter style unit that utilizes carbon and an electrostatic reciprocator or ESP. The latter charges particles as they go through the unit and collects them, while using carbon for odor removal. Filtered units cost half as much up front and twice as much to operate and the opposite is true for ESP units, which also have an automated wash system so filters don’t need replacing.
Ventilation systems come equipped with exhaust fans that can mount either on the facility’s roof, which is most common, or an outside side wall. Belt or direct drive fans are available, although direct drive has become more common, as it doesn’t include a belt that can be prone to breaking. For this reason, direct drive requires less maintenance and has a reduced risk of downtime.
When unbalanced or poorly designed kitchen exhaust systems can allow heat and smoke to spill into the kitchen, it negatively impacts air quality, back-of-the-house temperatures and utility bills. This also compromises cooking equipment. Ventilation systems’ make-up air units prohibit negative pressure in the back of house, improving air quality. The load generated by cooking units will determine how much make-up or replacement air is needed to balance the environment.
In addition, the air velocity around the hood needs to be minimized, or the ventilation system may be compromised. Four types of systems can accomplish this: one system brings in untempered air from outside into the kitchen; another brings in outside air and heats it; a system is available that brings in outside air and cools it and another both heats and cools outside air, depending on the temperature needed. DOAS or Dedicated Outside Air Systems also are available that provide complete temperature and humidity control of makeup air.
Ventilation systems’ fire suppression equipment and controls typically incorporate tanks of chemical agents that are activated mechanically to contain or extinguish fires. Newer systems have unlimited water supplies for this purpose. When a sensor at the duct connection gets to a certain temperature, this fire suppression system is electronically activated. Also, bigger hoods with more overhang and end panels can help contain fires.
Demand control kitchen ventilation or DCKV automatically varies the ventilation system operation to accommodate peak and down periods. This is accomplished with heat only, where sensors or optics measure the heat differences between the hood and the room. DCKV also can react to both the heat and exhaust, which typically results in a quicker reaction time.
It’s important to check regulations, as some state codes require DCKV if there are 5,000 CFMs (cubic feet of air per minute) of exhaust or more. Although these systems can be costly, the return on investment with energy savings is generally under two years.
When choosing a ventilation hood, operators should weigh a number of factors.
“Type 1 is required per code for
any equipment that reaches over 400 degrees F and produces grease laden vapors,” says Brent D. Hall, principel, vice president, Clevenger Associates, Puyallup, Wash.
Energy efficiency and local codes represent two key factors when choosing a ventilation system. “For example, in Seattle if you have a Type 1 hood and over 2500 CFMs of exhaust air, per code you have to run a demand control ventilation system,” says Hall. “With these systems, fans ramp up and down in speed so hoods don’t operate at full force when they don’t need to. Thermostats up in the hood detect temperatures coming off cooking equipment and determine how fast fans need to run. These systems are becoming code across the nation for energy savings.”
An exhaust fan auto start feature may represent another good investment for some operators. “Sensors inside hoods detect temperatures over 90 degrees and hood fans automatically turn on; these won’t turn off unless the temperature goes below 90 degrees for more than 15 minutes,” says Hall. “This is mandated in many locations, but may become a uniform mechanical code.”
Operators can choose from different types of control panels, with the sophisticated types costing significantly more. “However, these will be needed for those running multiple hoods to one exhaust fan, which can get pretty complex,” says Hall. “It can be difficult hooking up to ventilation system components provided by different suppliers. This requires more coordination between kitchen consultants and mechanical engineers.”
Some accessories can help reduce air volumes, including wing walls or panels. “Forty-five degree 2-foot-by-2-foot or 3-foot-by-3-foot panels help aid in catching air and lower air volume, but these also can hinder accessibility to the unit and bring down air volume slightly when needing to make code,” says Hall.
A growing number of larger cities, such as New York and Los Angeles, now require pollution control units as part of ventilation systems. “This component pulls grease and odor out of the air,” says Hall. “It scrubs air coming out of exhaust ducts, as well.”
Cleaning & Maintenance Considerations
Kevin McCaw, field supervisor, Hawkins Commercial Appliance Service, Englewood, Colo., says ventilation hood space is at a premium in today’s commercial kitchens.
“In many places, it’s not feasible to put in a hood,” he says. “For new kitchens, mechanical chases need to be created and run ventilation through floors.”
Ventilation needs professional cleaning every six months at minimum, and fire systems should be inspected at least annually. “The hood has visible filters that should be removed and run through a dish machine once a week,” says McCaw. “Cleaning depends on how much grease is in the air and hours of operation, but we recommend weekly for hood filters and every six months for hood cleaning as standard.”
Professional ventilation cleaners have access to each corner and bend of the ducts. It is not recommended operators take it upon themselves to clean out these areas with pressure washers. “This has resulted in many service calls for us, but it’s not a bad idea to wipe down hood interiors occasionally,” says McCaw, who adds that, because there are not many moving parts, ventilation systems can last as long as 60 years, with roof fans lasting 7 to 10 years on average.
If the ventilation system is not operating or there is a noticeable vibration, a service technician should be called. “Fans get out of balance if they’re dirty and shake themselves,” says McCaw. “If there is a big vibration when hoods are turned on, or there is excessive noise, it’s time for service.”
Also, if it feels like there is a wind tunnel in the kitchen, this is a sign the makeup air system isn’t working. It causes air pressure and sometimes a sewer gas smell because negative air is being pulled in,” says McCaw. “Makeup air is just as important as having the hood running.”