Commercial Kitchen Ventilation Lab
Size the exhaust for a commercial kitchen hood from its type, length and cooking duty, then the grease duct, make-up air and the cooling load of that make-up air in Gulf summer. Checks the wet chemical suppression interfaces and the grease duct rules, and shows what demand control ventilation saves over a service day.
How to use: pick the hood type and the heaviest cooking under it, enter the hood length and the outdoor design. Tap i for help.
1. Inputs
2. Kitchen ventilation
Section through hood and duct, a 3D kitchen and the exhaust over a service day with and without demand control.
3. Checks
Suppression and fire interfaces
4. Airflows and sizes
5. How it works
Exhaust rate
Type I grease hoods are sized per metre of hood length from the hood style and the heaviest cooking under it (IMC 507 and ASHRAE 154). An island canopy needs more air than a wall canopy because there is no wall to guide the plume. Heavy duty appliances such as char broilers and woks need much more than ovens.
Grease duct
NFPA 96 sets a minimum of 2.54 m/s (500 fpm) to keep grease moving, and designers often use 7 to 9 m/s. The duct is liquid tight and welded (1.37 mm carbon steel or 1.09 mm stainless), slopes back to the hood or a grease reservoir, has cleanout doors at every change of direction and runs in a fire rated shaft to the roof. Discharge at least about 1 m above the roof and well away from fresh air intakes.
Make-up air
About 80 to 90% of the exhaust is supplied as make-up air near the hood, and the rest transfers from the dining area so the kitchen stays slightly negative. In Dubai summer that outdoor air carries a large latent load, so make-up air units with chilled water or DX coils are often bigger than the space cooling.
Suppression
A UL 300 wet chemical system protects the hood, plenum, duct entry and appliances. When it discharges it shuts the gas valve and the power to cooking appliances under the hood, stops the make-up air and signals the fire alarm. Exhaust fans normally keep running to clear smoke unless the system listing says otherwise.
Concept sizing tool. Final airflows come from the listed hood maker, and the suppression design from the listed system installer and the local Civil Defence or fire engineer.