23 28 13: Commercial – Kitchen Hoods
The science of commercial kitchen ventilation includes both exhausting air as well as providing replacement air within the cooking area. Whether a restaurant is a small free-standing site or a large institutional kitchen, managing and balancing airflow is a complex issue.
It is a challenge to properly ventilate commercial kitchens, as they must moving large volumes of air through ductwork and equipment placement in very restricted spaces.
Overall design, construction, installation coördination, and maintenance are required to get greatest performance and an energy-efficient air balance from the system.
provides the information and drawings to Illustrate the elements of construction and installation of commercial kitchen ventilation systems.
The information is intended to encourage standardization in installations and to call attention to the proper segregation of responsibilities of those involved with food service design and installation.
A Typical System
A typical kitchen ventilation system includes an exhaust hood or canopy, duct-work, fan system, and a means of providing adequate make-up air. The entire system must combine a fire-safe assembly within the building.
Exhaust hoods and canopies capture heat and contaminants in the air by means of filters, extraction baffles (cartridges), and water mist systems. There are many style variations of hoods with canopy styles—a large box with and open bottom—being the most common.
Styles choice is based on the type of oven and the expected contaminates to be removed. While there are several styles of hoods, all fall within two major categories:
- Type I hoods carry a listing label and are manufactured and installed according to the manufacturer’s and listing agencies’ requirements. They are designed to handle grease and include a number of integrated components within the hood.
- Type II hoods are used in the collection of steam, vapor, heat, and odors—but not grease. The two sub-classifications of Type II hoods are condensate and heat/fume.
Exhaust ductwork provides the means to transfer contaminated air, cooking heat, and grease vapors from the hood to the fan.
- Ducts accumulate combustible grease and should be constructed from 16- steel or 18-Gage stainless steel as per code requirements.
- The ducts must me securely supported by non-combustible duct bracing and supports designed to carry the gravity and seismic loads as per code requirements, no fasteners should penetrate the duct.
- The duct is often run inside a shaft enclosure and that enclosure is typically constructed of gypsum board, plaster, concrete, or ceramic tiles and must be an approved continuous fire-rated enclosure.
Exhaust fans move the heat and contaminated air out of the building. All exhaust fan components must be accessible or have removable access panels for cleaning and inspection and must be designed to contain and drain any excess grease.
There are three major types of exhaust fans:
- Upblast fans are typically aluminum centrifugal designed for roof mounting directly on top of the exhaust stack.
- Utility fans are normally roof-mounted with the inlet and outlet 90 degrees from each other and are typically used where high-static pressure losses exist.
- Inline fans are typically in the interior duct and are used where exterior fan mounting is impractical.
In order for the exhaust system to work properly, make-up air is required to replace air equal to the amount removed. Make-up air can be provided via an independent system or in combination with the building’s HVAC system.
Kitchen Ventilation Concepts
To better understand why a kitchen ventilation system needs to be designed and constructed in a very specific way, the principles behind air movement must be understood.
Buildings are required to adhere to indoor air quality regulations and, depending upon the jurisdiction, sometimes exhaust air quality regulations.
The food service industry must meet higher air quality regulations than standard building exhausts due to the type of contaminated air produced by cooking food.
Exhaust air is the starting point in restaurant kitchen ventilation design. Exhaust air is the air that is contaminated by smoke and grease-laden vapor (aerosols) created by the cooking source.
This air must be removed from the building in a way that complies with local codes and ordinances.
Make-up or, supply air must be provided in about equal amounts to replace the kitchen air being exhausted. Typically, outside air is supplied through a designed make-up air system.
Most health codes require that an amount of fresh outside air be included in any replacement air calculation to aid in indoor air quality requirements.
The Kitchen Ventilation Team
The safety and design requirements of both commercial kitchen exhaust and makeup air systems must that a group of key players have enough knowledge of the subject to coördinate the entire process from design to operation.
The following overview provides a brief description of each team member with a vested interest in the process and suggests criteria necessary to design and install a comprehensive and balanced system that offers efficient operating costs, climatic controls, and satisfies building and fire regulations.
An owner/facility manager needs to understand the interdependence of each piece of the kitchen system to recognize the value of having a complete and properly integrated system that will give a productive and comfortable work environment that is also cost-effective.
The architect is responsible for the commercial restaurant’s design including fire-resistive walls, floor-to-ceiling assemblies, roof-ceiling assemblies, and the protection of openings as well as the horizontal and vertical smoke barriers.
In consideration for fire protection, the architects first must decide the overall function of the structure and the type of occupancy of its spaces.
The architect is also responsible to design right spaces within the building that are required to be separated by fire-resistive assemblies with protected openings, as in the local building code.
The architect will communicate and coöperate with the authority having jurisdiction at the building site and comply with any special conditions of fire protection design required by that authority.
Contractors must have access to and be able to use manuals and design rules to fully comply with design goals and specifications established by the kitchen ventilation system designer.
Local code authorities must be capable of judging adequacy and comparability in the installation of commercial kitchen ventilation systems and its components and assemblies.
The most critical aspects of a code official’s job are fire and safety issues. However, understanding the “standards of practice” that quality contractors strive to make is also important.
The engineer or system designer is responsible for knowing where ducts, pipes, and other conduits pass through required fire-rated separations or smoke barriers.
Duct penetrations must be shown on the mechanical plans and designed with an proper protection method. Use of standard symbols is highly recommended.
International Mechanical Code (IMC) and the National Fire Protection Association Standard # 96 Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations (NFPA #96), NFPA 17A and 90A, all state that the designer must show on the plans the location and mounting details of all automatic fire doors, dampers, access panels, and other fire protection means incorporated into both the exhaust and supply systems.
To coördinate all requirements, designers must have all necessary information on barrier locations, occupancy assignments, protection planning, rating, and identification of compartments and structural components.
Drawings must show fire and smoke dampers and heat stops. The engineer/designer should specify the hourly rating and type of damper and requirements for access doors.
Specific framing requirements of openings should be provided in the architectural and structural drawings submitted for building permits.
Thickness and type of fire resistive material may vary by jurisdiction. There should be coördination in advance with local authorities to verify the acceptance of the methods and equipment proposed for use.
RELEVANT CODES AND STANDARDS
Local codes are generally adopted from either the International Mechanical Code (IMC) or the National Fire Protection Association Standard # 96 Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations (NFPA #96) or a combination of the two with particular local issues of concern included.
In many major cities, local codes are written and published by local building officials; however, such codes are often based on one of the national codes before mentioned.
Certain government agencies such as the General Services Administration (GSA), the Department of Health and Human Services (HHS), Housing and Urban Development (HUD), and the U.S. Army Corps of Engineers have specific standards or codes that must be accommodated in construction performed for these agencies.
In some instances, the insurance companies that underwrite the building have recommendations or standards from the American Insurance Association (AIA).
Planners and designers need to find and consult the local authority having jurisdiction and local governing codes prior to designing a kitchen ventilation system.
Consideration must be given to both the building and fire codes.
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