Understanding your extraction system is crucial to running a commercial kitchen effectively. Heat, grease, steam and combustion gases are constantly produced in a commercial kitchen. Knowing how your extraction system deals with these factors will enable you to get the best from your equipment and highlight any potential problems before they become serious issues.
The Canopy Hood Captures Fumes First
Capture Velocity – How High Does Your Hood Need to Be?
The canopy hood is positioned directly above the cooking equipment in your kitchen. The function of the canopy hood is to capture all of the fumes produced by cooking before they spread to other areas of the kitchen. The contaminated air is drawn upwards by the extraction fan at a specific speed, referred to as the capture velocity. Typical capture velocities for commercial kitchens are between 0.25m/s and 0.5m/s at the hood face. This ensures that all of the rising fumes are drawn into the extraction system before they have a chance to drift off sideways.
What a Grease Filter Does
The air that is extracted through your kitchen extraction system passes through grease filters, typically baffle style aluminium panels. The baffle arrangement within the grease filter causes the air to take a number of sharp turns, which enables the grease droplets to be caught on the surface of the filter. The grease that is extracted from your cooking is caught within the grease filter, thus preventing it from travelling down the ductwork and causing a potential fire hazard.
How Ductwork Carries Air Out
The cleaned air is then carried through the ductwork made of steel, to be discharged outside of the building. The ductwork must be properly sealed, sized, and routed with as few bends as possible to maintain resistance and ensure proper airflow. A system that has been poorly routed can quickly lose performance due to friction in the ductwork.
Why Make-Up Air Matters
When a fan extracts a cubic meter of air it must be replaced by fresh air otherwise the kitchen will be drawn into negative pressure. This will have several effects, the doors may be very difficult to open, the flames from cooking equipment could be disturbed and most importantly the hood’s capture efficiency will be affected. This can be achieved by installing a make-up air unit, which could supply fresh, tempered air into the kitchen at a rate that matches the extraction from the hood.
Matching Fan Speed to Cooking Load
The extraction fans are generally variable-speed to ensure that the amount of air being extracted is sufficient to remove all the fumes from the kitchen, but also to keep the running costs as low as possible. This allows the fan to be increased in speed when required (e.g. when all grills and fryers are in full use) and decreased when not required (e.g. late at night when only microwaves etc are in use).
Keep Filters Clean
Blocked grease filters cause reduced ventilation and pose fire risk. Cleaning of grease filters should be done on a weekly basis for very busy commercial kitchens, however for less busy commercial kitchens with grease filters it may be suitable to clean every 2 weeks. For Commercial Kitchen Extraction see https://www.targetcatering.co.uk/kitchen-extraction/commercial-kitchen-extraction. The health and safety requirements for catering environments outline the commercial kitchen ventilation standards required.
A good extraction system will keep your kitchen safe, comfortable and comply with health and safety regulations.