A Commercial Kitchen Ventilation Primer for Startups

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A commercial kitchen ventilation (CKV) system should remove the excess heat to provide a comfortable working environment for your kitchen staff. More than that, the system removes humidity, grease, particulates and other cooking byproducts from the kitchen environment. While doing all this, it must maintain a balance of airflow within itself, and with the rest of the restaurant. And finally, it also serves as an integral component for kitchen fire detection and suppression.

Robert N. Rossier

Mom used to have a saying: "If you can't take the heat, get out of the kitchen." She wasn't talking about cooking, per se, or kitchens either for that matter, but in the restaurant business, it seems to apply more often than not. All too often the kitchen environment is heated, and with heat, unhappy workers, flared tempers and general chaos, confusion will follow.

But a hot kitchen environment is more trouble than all that. High temperatures mean that chillers, refrigerators and freezers must work overtime to keep things cool, and that takes additional cold, hard cash in the form of utility

bills. As studies show, high temperatures also take a toll on employee productivity, and that can cost a pretty penny, as well. If you can't take the heat in your kitchen, you could take my mother's advice and just get out. Better yet, maybe it's time to see what's going on with the ventilation system.

CKV Basics

kitchen fire detection and suppression.

While these basic requirements may seem simple enough, the design of an effective and efficient CKV system is anything but simple. First, the system must comply with a range of design codes imposed by state and local building authorities, health departments, fire marshals, insurance companies and even OSHA. Next, the demands imposed on the CKV system fluctuate with daily cooking demands, and with daily and seasonal climate changes.

The take-home message here is that designing a compliant CKV system, or modifying one, is not something a restaurant owner should tackle alone, but rather should involve a CKV design professional. The responsibility for maintaining the system, however, and ensuring its cost-efficient and safe operation falls squarely on the shoulders of the restaurant operator. And that requires a fundamental knowledge of how the system works.

The CKV system has several key components. First are the ventilation hoods that draw heat, steam, grease and smoke away from cooking devices and other equipment. All or part of this air is filtered to remove grease and other particles, and is then ducted to an outlet on an exterior wall or the rooftop. The hoods that collect grease and smoke are equipped with fire suppression systems to limit the danger of grease fires. Finally, fresh air to replace that which is removed is brought into the building through a dedicated ducting

system, via the central HVAC system, or by some combination of both.

Ventilation Hood Basics

The most basic component of a CKV system is the ventilation hood, also known in some parts as a canopy. These come in a variety of styles and designs to accommodate a variety of needs. First, ventilation hoods and the ductwork that services them are classified according to the types of demands they service. Those that serve components such as deep-fat fryers and grills that produce smoke and grease are classified as Type I.

Type I hoods must be water-tight to contain that smoke and grease, and are equipped with a built-in fire suppression system. Those designed primarily for the removal of waste heat and moisture (steam) are classified as Type II hoods, and don't require the sealed design or fire suppression system.

State and municipal building and fire codes define the requirements for kitchen ventilation in general, as well as specific requirements for ventilation hoods. Ventilation hoods may be required for a variety of kitchen appliances, including stoves, ovens, steam kettles and grills. They may also be required for items such as ware washers that pump a plume of hot, humid air into the workplace. In general, the codes will require a specified airflow in

cubic feet per minute (CFM) based on considerations as the type of appliance, the area of the hood, or the linear feet of hood base.

Cooking appliances are generally classified by the amount of heat, smoke, steam and contaminants they produce, as well as the "thermal plumes" they exhibit. The thermal plume refers to the shape and characteristics of a turbulent cloud of heat, steam, smoke and contaminants rising off the surface of the cooking surface. Cooking appliances are classified as light-, medium-, heavy-, and extraheavy-duty, depending on the thermal plume characteristics and overall quantity of heat, smoke and grease emitted.

An important thing to remember is that codes vary from one location to another. An appliance that requires a ventilation hood in one state, municipality, or specific setting may not require that hood in another location or setting.

Hood Designs

One of the more common hood designs is called a baffle or filter hood; however, these are becoming disfavored. Baffles were designed for fire suppression, not grease trapping. This "primitive" design draws low-velocity air through a short series of baffles or filters.

Although simple, these hoods aren't too effective, typically removing only 30 percent to 35 percent of the grease entrained in the airstream. In addition, they can be difficult to keep clean, and may not meet existing codes.

More common in many restaurant applications requiring a Type I hood is the centrifugal extractor hood. Unlike the simple baffle hood, the centrifugal extractor hood draws air at a substantially higher velocity, pulling it through a more tortured array of baffles and filters where both grease and particulates impinge due to their mass and high velocity. Efficiency

for extractor hoods generally runs about 60 percent.

Centrifugal extractor hoods come in two basic varieties: wet and dry. The wet extractors, or "water wash" systems, incorporate a sophisticated array of

spray nozzles that inject a mixture of water and detergent at predetermined times to suppress fires and provide some filter cleaning.

The most efficient hoods on the market, in terms of removing grease, are "two-stage filtration" types. These incorporate a centrifugal extractor followed by a filter, which uses reagents to absorb fine grease particles. These can remove 80-85 percent of the grease from the smoke.

Regardless of the design, all hoods must draw air from the kitchen, and fresh air to take its place comes from elsewhere. Generally, this "makeup air" (referred to as MUA in the trade) comes from outside, and conditioning it to the appropriate temperature and humidity level is an expensive proposition. Better hood systems and improved CKV design strategies have been developed to minimize the required MUA, and thus keep costs in line.

Research sponsored by the California Energy Commission reveals that back wall supply (aka "rear discharge") hoods can effectively accommodate a much greater proportion of outside makeup air, up to 60 percent of the required exhaust flow.

Vent Hood Fire Suppression

Building codes now require most restaurants to install in the hoods over cooking equipment (Type I ventilation hoods) fire suppression systems. Generally, these systems are integral with the hoods they serve. Two primary types of suppression systems are commonly used: dry chemical and inert gas. Dry chemical systems douse the fire with an extinguishing agent (typically sodium bicarbonate), which combines with the grease to form soap. Once the fire is out, the residue is readily washed away. Inert gas systems

usually employ carbon dioxide (CO2) to effectively cut off the oxygen supply and smother the fire. Although CO2 is generally considered nontoxic, all personnel should still be evacuated in the event of a fire.

Makeup Air Systems

They say that what goes up must come down, and while that may be true of

temperatures, the only way to make the CKV system work is to ensure that what goes out also comes in. To this end, it is essential that the system includes a well-conceived makeup air system, and that's the next major element of the CKV design.

Makeup air systems come in two distinct varieties -- conventional and short cycle -- and most commercial kitchens use a combination of both. The short cycle systems include the above-mentioned hoods, such as compensating hoods and air-curtain designs that draw some amount of makeup air directly from outside and then discharge it back into the hood service area.

While some MUA systems might simply allow fresh makeup air to enter from an open window or a louvered vent, a more common arrangement is to provide makeup air to the kitchen area through a system of fans, ductwork and filters. Most conventional systems provide conditioned air from a dedicated system or via the central HVAC system. Exactly how and where that air is distributed can have a marked effect on the operation and efficiency of the overall CKV system.

Makeup air can be distributed via a number of strategies, including the use of a variety of different ceiling diffusers, slot diffusers, floor- or wall-mounted displacement diffusers, and direct transfer of air from other areas within the building. However, proper design is essential to ensure appropriate airflow patterns. Crosscurrents that disrupt the airflow into hoods can markedly reduce their effectiveness. Cold air blasting in at the wrong place

might not only interfere with the food prep processes, but could unintentionally chill foods intended to be served hot. A poor makeup air design can not only cause annoyance and discomfort, but it can end up costing money as well.

If a substantial flow of cold makeup air is required, one effective strategy is to bring it in over the icemaker, where it reduces energy demands and minimizes condensation. Locating diffusers in areas such as compressor racks can help resolve problems in hot spots.

Various design codes may determine the general design of the MUA system, if not some important details. For example, state and municipal building codes may require that the makeup air be heated or cooled to within 10 degrees of room temperature. Often such systems will integrate with the central HVAC system, or will incorporate dedicated cooling and a direct-fired gas heater to cool and warm the incoming air. To keep energy costs in line, many systems now incorporate air-to-air heat exchangers, which transfer heat energy between the exhaust and makeup air.

One highly effective strategy is to transfer air from the dining area to the kitchen. Codes require a substantial amount of conditioned air be provided in the dining area, so rather than discharge it outside, many designs now take advantage of it in the kitchen. In fact, sources at the Fisher-Nickel Inc., Food Service Technology Center recommend transferring up to 60 percent of the kitchen's makeup air requirement from the dining area, if required and available.

Improving Efficiency

Since it costs money to condition air brought into a building, a goal in kitchen efficiency is to minimize the amount of makeup air required. This means limiting the amount of heat, humidity and smoke produced in the kitchen, and using effective, efficient ventilation hoods. Obviously, any effort made to reduce the head load in the kitchen, such as through the use of refrigerators/freezers with remote (outside or rooftop) compressors, or high-efficiency cooking equipment, will help achieve this goal. However, other strategies can also be applied to the problem.

When designing a kitchen, or installing new appliances, it often pays to select a "listed" or "approved" ventilation hood, since these can usually be operated at a lower exhaust air flow rate while still capturing and

containing heat and contaminants. Lower exhaust rates means lesser MUA requirements, ant that translates to fewer dollars. Other strategies such as the use of side panels, angles, flanges and deflectors can greatly

improve the capture and containment efficiency of a ventilation hood, thus minimizing the required exhaust flow, and associated MUA requirement.

Another strategy is to go high-tech. A relatively new entrant in the CKV world is called the "smart vent hood," which incorporates microprocessor-controlled variable- speed fans.

These systems use measurements from photoelectric smoke and heat detectors to

determine the proper ventilation rates. One such hood is the Intelli-Hood™, but retrofit technology for existing ventilation systems is also available. Sources at Florida Light and Power suggest that such systems can significantly reduce energy costs in commercial kitchens, often with a one- to two-year payback period.

CKV System Maintenance

Maintaining the CKV system is not something to be overlooked. One of the most common causes of fires in restaurants is improperly maintained (i.e., not properly cleaned) ventilation hoods and exhaust ducts. To avoid grease fires, it is critical that hoods and ducts be regularly cleaned, and that grease accumulations in grease extractors be removed at least daily.

Another technology that's being used to extract grease is ultraviolet (UV) lighting; however, its efficacy is for this purpose debated. The theory is that UV light initiates a chemical reaction that alters grease and grease vapors. To mitigate the risk of vent hood and exhaust duct fires, make certain that periodic inspection of all fire detection and suppression system components is part of the general maintenance procedures. A faulty or failed system can spell untold trouble if an incident should occur.

Remember that air filters in the MUA system must also be regularly inspected, and cleaned or replaced. Not only can clogged filters reduce the makeup airflow and cause problems with the ventilation exhaust hoods, but they can also spell trouble in the form of burned out fan motors.

Proper maintenance also means keeping an eye on the operation of the ventilation hoods. But remember, just because an exhaust hood is drawing air doesn't mean it is working properly. If the hood can't draw enough air, the result may be a smoky, hazy kitchen. If insufficient makeup air is available via the supply system, reduced pressure in the kitchen could draw excess cold air from the dining room or other transfer areas, putting greater demands on the HVAC system.

Don't Let Your Guests Sense That the Back of the House is 'Fuming'

If an exhaust system isn't operating properly, the result could be a pressure increase that drives fumes and odors into the dining room -- not good for customers or business in general. In addition, if the exhaust system isn't functioning properly, that means the kitchen is going to heat up. And if you're like me, sometimes you just can't stand the heat in the kitchen.

- Restaurant Startup & Growth

Grease Filter and Exhaust Duct Cleaning

Perhaps one of the most often-neglected maintenance tasks in any kitchen setting is proper cleaning of the grease filters. This task should be performed on a weekly or monthly basis, depending on the type of restaurant, and the amount and types of food prepared. Grease buildup is a serious safety hazard, and is a leading cause of kitchen fires.

Modern CKV filters are either 16" x 16" or 16" x 20," which allows them to be washed in a commercial dishwasher. Even the best filters are less than 100 percent efficient, and some of the grease will find its way into the exhaust ducts where it can accumulate to dangerous levels over time, causing fire and health hazards as the grease becomes a breeding ground for mold and bacteria. If you don't have the expertise or staff to periodically clean and maintain the

ductwork, it may be one of those jobs best farmed out to a contractor or professional duct cleaning services for periodic inspection and maintenance.

Initial Sources

UpYourStack.com, an information resource serving the commercial kitchen ventilation (CKV) industry, identifies 13 categories of CKV equipment, including hoods with dampers, hoods without dampers, ductless hoods, grease filters, prefabricated grease duct enclosures, fans, hood and duct accessories, grease collection systems, fire extinguisher

systems, controls, utility distribution systems, and pollution control systems. While an exhaustive (no pun intended) list of every supplier is especially prone to omissions and errors, given the complexity and scope of CKV equipment, below is a substantial list of suppliers and Web addresses. As always, if you believe your company is not properly represented in a list of suppliers, please notify the editor at rsg.editor@spc-mag.com.

For more information on CKV systems, visit the Fisher-Nickel, Inc. Food Service Technology Center at www.fishnick.com and The American Society of Heating, Refrigerating and Air-Conditioning Engineers at www.ashrae.org.

Commercial Kitchen Ventilation Suppliers

Acme Engineering & Manufacturing Corp.

www.acmefan.com

Amerex Corporation

www.amerex-fire.com

American Coolair Corp.

www.coolair.com

American Hood Systems Inc.

www.americanhood.com

Ansul Incorporated

www.ansul.com

Avtec Products, DI Foodservice Companies