Commercial Kitchen Exhaust Hoods

A Guide to Commercial Kitchen Ventilation: Commercial Kitchen Exhaust Hood Placement and Capture Efficiency.

This article focuses on the hood design and their placement, capture, and containment. The hood system U.L. 710 listing only provides the minimum installation requirements based on fire safety requirements. There is significantly more involved when designing for energy optimization and excellent indoor environmental quality. From a code perspective, commercial kitchen exhaust hoods are the first line of defense to protect against a possible fire. Because of their significant impact on energy costs, care should be taken to select a system that also provides the most energy efficiency.

Hood design and placement, factors that influence the choice and type of exhaust hoods:

  • Different types of cooking equipment generate varying amounts of heat, grease, and smoke. The selection of the appliances is left to the food service consultant or Chefs based on the cooking requirements of the venue. Notably, the load generated by the appliances directly correlates with the amount of exhaust required to remove the load. The amount of exhaust is a function of the efficiency of the hood. Appliances generate both radiant heat and convective heat. It is the convective heat, the transfer of heat energy to the air, that we must calculate. This plume also contains grease particulates, vapors, and smoke.
  • Hood designs come in a variety of configurations; the most common are:
    • Canopy, (wall or double island)
    • V bank (single island, grease filters in a V arrangement in the middle)
    • Back shelf (popular with quick service restaurants)
    • Pizza oven (specifically design to be closed coupled with the oven)
    • Hybrid (combination of a canopy and backshelf)
    • Dishwasher (Type II, not for use with grease-laden vapors)
  • The physical size of the exhaust hood is a function of where the hood is placed in the space and the overhang required to “cover” the appliances. U.L. 710 test results identify the minimum overhangs mandated by the listing but may not sufficiently provide coverage for “real world” applications. Many manufacturers have software that calculates this overhang.
    • End overhangs are typically 6” to 12” for wall canopies. The heavier duty appliance, such as a charbroiler on or near the end of a line, would dictate greater overhang.
    • Ovens, lighter duty appliances can be satisfied with a 6” overhang.
    • Front overhang should not be neglected. A minimum of 12” and more commonly 18” or more especially when combi ovens are used to account for the door opening.
    • For island hoods, the starting point is 12” overhang, as the hood is open on all sides.
    • Back shelf hoods typically have some form of end panel integrated into the hood design, so standard overhang requirements do not apply.

What is capture and containment efficiency and how does it impact the design?

The exhaust hoods are put through a series of capture and containment tests. The test set up uses thermal imaging and space temperature sensors to determine the point of full capture containment. The use of thermal imaging allows you to visualize convective heat that is not visible to the naked eye. A combination of typical appliances are used. A combination of ovens, fryers, charbroilers and griddles are set up in varying configurations to test the hood’s ability to remove the load generated. This test is a more realistic one to demonstrate the effectiveness of exhaust hood, but even with these results, the manufacturer should be consulted to determine the proper exhaust rates for the given appliance load.

Look for the next articles where we will be covering
• Grease filters and their effectiveness
• Balanced make up air

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