Foodservice Equipment Reports
Special Features Ventilation & Custom Fab

Anatomy Of A Hood

Back in 2006, the Foodservice Consultants Society Int’l. published a white paper, “Commercial Kitchen Ventilation ‘Best Practice’ Design and Specification Guidelines,” that is relevant today. In one section, the document states that the appropriate exhaust rate—meaning a hood is operating the way it should to clear effluent from a cook line and maintain air quality and balance in the space—always depends on:

• The type, energy source and use of the cooking equipment below the hood.
• The position of the cooking equipment below the hood.
• The style and geometry of the hood itself.
• How the makeup air—conditioned or otherwise—is introduced into the kitchen.

While the “American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Handbook—HVAC Applications” establishes minimum ranges for CKV exhaust rates, ASHRAE Standard 90.1, “Energy Standard for Buildings Except Low-Rise Buildings,” establishes maximum exhaust-rate recommendations, which are being adopted into state building codes, including California’s last July. The maximums fall within the ranges in the handbook, but below the high end of those ranges. When it comes to energy efficiency, California often is considered a harbinger of codes to come. The first question everyone needs to ask when engineering and installing a CKV system is, “What is the maximum amount of air I can take out of this space?” The design and engineering of the CKV system needs to be considered first, not last, in the design process, and these systems need to be designed very well.

Following are some of the basic dos and don’ts of good CKV-system design (Type I hoods):

• Makeup air: Introduce makeup air gently and slowly, allowing the thermal plume of the cooking equipment to rise into the hood undisturbed. Makeup air from perforated linear plenums outside of the hood perimeter or transfer air are preferred. 

• Sizing: Make sure the hood is sized to have adequate overhang on all open sides and the capture area is large enough to contain all of the effluents produced from the equipment below, including equipment that involves opening a door.

• Construction: Look for hoods engineered with angles, curves, deflectors and/or flanges to contain, direct and capture effluent. Ductwork on Type I hoods needs to be liquid-tight. 

• Fire-suppression system: Your fire-suppression system should be code-compliant UL 300-listed, checked and double-checked.

• Demand-controlled kitchen ventilation: DCKV is the most effective way to increase the energy efficiency of your CKV system. 

• Back gap: The gap between the back of equipment and the wall benefits from being minimized or capped as the air might be pulled up through the gap and disrupt draw efficiency. Enclosing or minimizing the open area between the back of the cooking equipment and the hood wall can increase hood performance.

• Equipment placement: Heaviest-duty equipment (charbroilers, wok ranges) go in the center of the cook line under the hood; lighter-duty equipment (steamers, fryers) go on the ends. 

• Minimize plume disruption: Ceiling diffusers, especially four-ways, nearby doors, stand fans and makeup air introduced at too-high a velocity, will decrease hood performance.

• Filters: Filters should be accessible, easy to change and easy to clean. UV options are helping to decrease grease buildup in exhaust ducts. 

• End panels: Small and large end panels can increase a hood’s capture-and-containment efficiency.

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