Can't Stand the Heat? Check Your Kitchen Ventilation Systems

Food service facilities use far more energy per square foot of building space than the typical commercial building. The kitchen ventilation system, while critical to food service operations, is a key contributor to that high energy use. These systems remove heat, smoke, grease and carbon monoxide, as well as steam from cooking and dish washing.

A poorly maintained ventilation system not only wastes energy, it reduces safety, as well as worker comfort and productivity. Understanding how a kitchen ventilation system works is important when taking steps to increase energy efficiency and improve system performance. For handling kitchen effluents, a basic ventilation system consists of a hood or canopy, ductwork and a fan.

The Hood

The hood captures the plume of heated air that rises from the cooking surface. A key component is the grease filtering system, typically based on one or more of the following technologies:

• Mesh filters consist of layers of metal mesh, which trap grease and contaminant particles as air is drawn through. They're not effective at removing high levels of grease, and require frequent cleaning.
• Baffle filters separate grease from an air stream by changing air speed and direction. They're more efficient than mesh filters and can be cleaned in dishwashing machines.
• Cartridge filters are suitable for moderate to heavy grease environments. These stainless steel filters can be cleaned in commercial kitchen dishwashers.
• Water wash cleans the cartridges in an automatic internal washing cycle. They require a direct hot water supply and are typically costly to install.
• Continuous water mist is very effective because it uses a continuous mist of cold water sprayed into the extraction system. Fats are emulsified and dropped into a collection trough.
• Ultraviolet integrates ultraviolet lights into the hood. The light breaks down grease molecules into smaller compounds of carbon dioxide and water vapor, which are removed by the exhaust airflow.

The Exhaust Fan

The three types of exhaust fans typically found in commercial kitchens are:

1. Upblast fans are aluminum mushroom-shaped fans commonly seen on restaurant roofs. They're designed to emit kitchen exhaust away from the roof. Direct-drive fans, which have no drive belt to wear out, can save energy by running at variable speeds.
2. Utility sets are roof-mounted units made from steel capable of handling large volumes of air as well as high temperatures. They're easy to clean, reducing maintenance costs and increasing equipment life.
3. Inline are axial fans and although rarely used in food service settings, have some application in minimal grease environments.

Ductwork

Ductwork for cooking exhaust systems is typically made of stainless steel. It should be liquid tight, designed with easy access for cleaning and routed vertically to the roof as much as possible with minimal turns.

Improving Kitchen Ventilation Efficiency

These simple steps will save energy and help maintain a safe and comfortable kitchen environment:

• Ventilation systems work less efficiently with too much or too little makeup air; make sure you have the right amount. Integrate your kitchen ventilation units with the HVAC system, bringing in air from adjacent work or serving areas.
• Minimize makeup air velocity near the canopy or hood; it should be no more than 75 feet per minute.
• If you have a variety of cooking appliances or a variable schedule, consider using exhaust fans with adjustable speed controls.
• Arrange cooking appliances based on how much effluent they produce. Specify ventilation rates accordingly. Position heavy effluent producers, such as char broilers, in the center of a hood section.
• Ensure that access panels are properly installed and sealed, and that ductwork is accessible for cleaning.

With these measures, you help keep your kitchen environment safe, comfortable and productive.