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Commercial Kitchen Ventilation Exhaust Hoods


©2015 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 57, no. 11, November 2015

By Don Fisher, P.Eng., Member ASHRAE; Rich Swierczyna, Associate Member ASHRAE; Angelo Karas

About the Authors
Don Fisher, P.Eng., is principal of Fisher Consultants, LLC, Danville, Calif., which provides technical and management consulting services to the PG&E Food Service Technology Center (FSTC) in San Ramon, Calif. Rich Swierczyna, senior engineer at Fisher-Nickel, Inc., San Ramon, Calif., manages testing at the Commercial Kitchen Ventilation Laboratory and Angelo Karas is a senior lab technician at the PG&E Food Service Technology Center in San Ramon, Calif.

The science of commercial kitchen ventilation (CKV) continues to evolve at a rapid pace, driven by ASHRAE research projects, an expanding line of high-performance and innovative products, and ongoing testing by various organizations and research facilities. All of this information, along with the results of a California Energy Commission-funded makeup air research project, is leading to updates of the national codes (ASHRAE Standard 154, NFPA 96, UMC, ASHRAE/IES Standard 90.1 and California Title 24) and fundamentally changing the way CKV systems are designed and operated (e.g., application of demand-controlled kitchen ventilation).

ASHRAE’s comprehensive 39-page Handbook—HVAC Applications chapter on kitchen ventilation is a dramatic improvement over the two paragraphs in the Handbook that existed when the authors began their careers in kitchen ventilation. However, there are still many details associated with the installation of exhaust hoods, makeup air systems, and appliance layout that are overlooked (or not recognized for their importance) within the design and specifications for CKV systems. This article focuses on CKV system attributes and installation best practices that have been identified and/or quantified through public-domain research (as referenced above).

“Hot air rises!” This introductory sentence to a design guide series coordinated by the authors states the obvious. So why then does the thermal plume off cooking equipment sometimes rise and stay within the hood reservoir, while at other times it fills the kitchen with smoke, grease, and heat? Research sponsored by ASHRAE has provided intriguing insights into this question. In addition to the more obvious “it depends on the amount of exhaust air” factor, research has demonstrated that hood style, construction features and installation configurations, makeup air introduction, as well as the positioning of appliances beneath the hood had a dramatic influence on the ability of the hood to capture and contain.

By making what might appear to the design engineer, installing contractor or kitchen manager to be subtle changes, a surprisingly wide range in the exhaust rates required for complete capture and containment (C&C) of cooking effluent can result due to appliance position and/or hood installation details and configuration. Within the real world of commercial food service, this explains why an identical exhaust hood installed over virtually the same appliance line performs successfully in one kitchen and fails in another.

However, as stated, such attributes (often outside the direct responsibility of the hood manufacturer) are often neglected within the CKV design specifications (e.g., end panels, appliance placement, overhang, space behind appliances, size of hood, etc.). The key to optimizing CKV performance is in the design details.


Hood Factor: Capture and Containment

First, the design exhaust rate that is the foundation for capture and containment (C&C) depends on the hood style and construction features. Driven in part by standardized test methods and their application by third-party laboratories, many aerodynamic features have been integrated into the design of leading brands of listed hoods (e.g., flanges or lips along the hood’s lower edge, air jets, filter position and size, elimination of filter shelf, etc.). Wall-mounted canopy hoods, island (single or double) canopy hoods, and proximity (backshelf, pass-over, or eyebrow) hoods all have different capture areas and are mounted at different heights and horizontal positions relative to the cooking equipment (Figure 1).

 Commercial Kitchen Ventilation Exhaust Hoods - Figure 1

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