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Kitchen Ventilation System Maintenance and Safety

Many operators learn the hard way that their kitchen ventilation system is set up inefficiently. The costs can be significant. Consider finding out that your hood system was designed poorly from the get-go when all you wanted was a contractor to fix it when it stopped working.

This is often the case. The typical independent operator installs a hood system, cleans it as often as local codes require, and does not otherwise think about the hood until something is not operating correctly.

Ventilation System Anatomy

Equipment nomenclature is important to understanding your system and having productive conversations with consultants, contractors, and repair technicians. Here is a rundown of the three primary components of your kitchen's ventilation system.

The Hood The kitchen hood collects and removes grease, vapors, and other volatile compounds produced during the cooking process by broilers, fryers, griddles, ovens, and ranges. Today, hoods have controls or sensors that allow operators to adjust the suction power of the hood, often depending on the number of appliances in use; thus, conserving energy. The hood connects to a ductwork system, which carries vapors out of the kitchen.

In this article, we look at the basics of kitchen hood maintenance, as well as tips on kitchen ventilation design to optimize efficiency. The savings can mean hundreds of dollars or more every month.

There are two types of commercial kitchen hoods. Type 1 hoods, sometimes called "grease hoods", are installed above appliances that produce grease. These hoods must be cleaned regularly to prevent grease fires, and are subject to NFPA 96, Ventilation Control and Fire Protection of Commercial Cooking Operations standards from the National Fire Protection Association.

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NFPA 96 Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations

Type 2 hoods are also called "condensate hoods". They are installed to serve appliances that do not produce grease. Type 2 hoods do not need to comply with NFPA 96. It is vital to understand which style of hood your concept has, so you can follow the appropriate guidelines.

States and municipalities set their own standards regarding hood size and performance. These tend to dictate the performance of the hood in terms of how many cubic feet of air flow are exhausted per minute (CFM). In the past, a higher CFM number was desirable. That said, Terry Brumback, president of Brumback Restaurant Equipment, Inc in Decatur, Alabama, explains that these days, hoods are more efficient so CFM numbers tend to be lower. "A highly efficient hood will take out less air."

Ductwork. Ductwork removes air sucked up by the kitchen hood and carries it outside. There are ductless hoods, also known as recirculating hoods. These do not vent air outside using ducts and external exhaust fans. Instead, they capture the smoke and grease using filters, then recirculate the air back into the kitchen.

Richard Young, director of Outreach at Frontier Energy Food Service Technology Center in San Ramon, California does not recommend ventless hoods for the typical restaurant cookline unless there is no other choice. They do not remove heat from the kitchen and they require more maintenance.

Operators may have another missed opportunity with ductwork, says Brumback. The ductwork commonly used in restaurants is square. However, there is a newer type of ductwork that is rounded. Rounded ductwork creates less friction inside, so it is more efficient. It is laser tested to ensure there are no leaks and comes with a 10-year warranty, Brumback notes. Choosing rounded ductwork in a new build or when replacing faulty ductwork can save money.

Fans. Fans propel the air taken in by the hood through the ductwork system. Fans also provide make-up air (MUA), which is fresh air that makes up for the contaminated air removed by the hood system. Fans benefit from routine maintenance to keep them in good working order. When maintenance is skipped, components such as belts and bearings may fail prematurely.

Making a Good Choice

Often with the help of expert consultants and contractors, startup operators can design their kitchen ventilation system from start to finish to conserve energy and save money. The design process typically consists of several steps:

1. Developing the kitchen layout including what appliances go where and the classification of appliances as heavy, medium, or light duty
2. Determining the ideal appliance layout for ventilation purposes, taking best practices into account
3. Selecting the type of hood, size, style, and features
4. Calculating the right airflow rate for exhaust, considering the appliance load and hood style, such as wall-mounted versus back shelf
5. Determining makeup air (MUA) strategy and location of diffusers

Designers consider the concept, menu, and location of appliances. A broiler creates more grease and vapor than a griddle. A burger concept that uses a broiler to cook patties will produce more exhaust than a burger concept that uses a griddle for their burgers. Placing the broiler in the center of the line, directly under the hood, is more efficient than putting that same broiler at one end of the line, where it is near the end of the hood system. Positioning of an appliance can have an impact of up to 30 percent on vapor capture and containment.

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Selecting & Sizing Exhaust Hoods Improving Commercial Kitchen Ventilation (CKV) System Performance Design Guides

Some appliances send out a burst of air when opened or closed. Think of convection ovens or steam kettles. A hood with a large overhang will easily capture the rush of air these appliances create, while one with a smaller footprint may miss some of the surge. The factors add up to a big difference in air quality, energy use, and operational cost.

As suggested above, operators can lean on consultants to advise the ideal setup and adhere to local regulations. When selecting a commercial kitchen hood, Brumback recommends operators look for NFPA (National Fire Protection Association) and UL (Underwriters Laboratory) certification. UL is a not-for-profit organization whose goals are to establish, maintain, and operate laboratories for the investigation of materials, devices, products, equipment, constructions, methods, and systems with respect to hazards affecting life and property.

These standards indicate the hood is high-quality and energy-efficient. Exhaust fans and MUA fans will also have UL stickers and energy-efficient ratings. The most efficient of these will have Energy Star ratings, too, he notes.

The most efficient hoods include a variable frequency control system that reduces energy consumption and saves money. "This allows the motors to ramp up or slow down based on the number of appliances that are operating under the hood. If you are only using one or two appliances, your exhaust fans will run at a slower rate," Brumback explains. There is more information on how these save money in the section on money-saving tips below. Another useful feature is a prep mode, which draws a minimal amount of air when prep cooks are working.

Maintenance

States and municipalities provide guidelines regarding commercial kitchen hood maintenance, hood size, and other topics. So do insurance companies. Operators should check what their state and insurance company require, then factor that information into their planned hood maintenance schedule.

Typically, operators will need to have the hood steam cleaned every six months, or as often as their location's codes require. Heat from the steam will loosen caked-on grease more effectively than a chemical cleaning. The hood filters can be run through the dishwasher, as often as every few days.

Alongside cleaning the hood at the frequency indicated by municipal guidelines, Brumback recommends a preventative maintenance program to keep the system in good working order.

"Have an HVAC technician go up on a regular basis and look at the fans on top of the building," he says. The technician will check the belts for signs of wear and tear, tighten belts to the correct tension, and advise operators if replacement is recommended. They will grease the bearings so the system operates as it should. "When we see hood fan failures, it's generally in the belt and bearings," Brumback says. "If we do not maintain those bearings, they dry out. Not only does the bearing go out, it causes damage to the shaft which causes us to replace the fan completely."

When properly maintained, Brumback says, fans will operate for a long time. Problems arise when maintenance is neglected. This can be an issue when restaurant operators inherit a kitchen ventilation system that a previous owner did not properly maintain, and must pay to fix issues that could have been prevented with proper maintenance.

Brumback says it can be difficult to find an HVAC technician with the skill set to make complex repairs. As a result of the skills gap, operators may find themselves replacing a component of the ventilation system for something that "would've been considered minor damage 20 years ago," he says.

With routine maintenance, the hood system will last a long time. Ductwork tends to have a shorter life span, particularly if it is the older, welded kind. Frequently, the welds begin to fall apart. Grease gets into the system and clogs the airflow. Eventually, the ductwork needs to be replaced, he says. It is generally not practical or cost-effective to try to repair, especially when replacement with the rounded style can save money.

Lastly, hood systems will need to be inspected by the fire department. For Type 1 hoods, NFPA 96 requires two inspections per year of kitchen hood fire suppression systems. These inspections make sure the system will cut off gas or electricity and put out a fire if there were to be a fire. The inspection is a lengthy process that can impact the restaurant operation, but it must be completed.

Money Saving Tips

An inefficient exhaust hood costs your operation money. How much money depends on several factors including whether your ventilation system is appropriately sized for your kitchen setup, whether your ventilation system is spilling heat and smoke into the kitchen, what type of equipment is beneath the ventilation hood, and environmental factors, including your restaurant's location and the exterior temperature.

"You go in the kitchen and it is loud. There is a lot of air moving. Something that loud is a sign you are using a lot of energy," Young says. Every exhaust hood has an exhaust fan pulling air out of the building and another makeup air (MUA) fan replacing that air as well as a heating system and a cooling system. For operators interested in the energy efficiency of kitchen hood systems, it is important to pay attention to every part of those systems.

Young suggests that operators reduce the number of cubic feet of air moving through the kitchen by optimizing exhaust systems. It takes energy and money to move every cubic foot of air up the ductwork, and replace it with MUA. "Because a kitchen ventilation system is once through, there is no recirculation. You pump it in, it goes across and it is sucked out very quickly," he says.

The good news is, there are three highly effective ways to optimize exhaust systems and reduce moving air that do not cost a lot of money. That is where Young recommends operators start. If appliances are installed against a wall, push appliances as close to the wall as possible. This reduces the space behind appliances, allowing the hood to better "capture and contain" vapors. It also gives the hood a bigger front overhang, so it can more effectively suck up contaminated air.

If possible, you can seal the gap between the appliances and the rear wall using a shelf or ledge.

A simple yet surprisingly effective tactic is to use side panels or skirts on the end of the hood. Side panels increase the airflow across the front edge of the hood while also reducing turbulence and cross drafts at the sides of the hood. The side panels do not necessarily need to be that large. Your hood's manufacturer can recommend appropriately sized panels.

If MUA vents are located close to the hood, so that they blow air across its face, the resulting pressure drop can stop the hood from operating properly. Moving MUA vents away from the hood or changing the style of vent to one with less velocity will save energy, which saves money. Young suggests turning three-way diffusers around so they face away from the hood, or swapping out finned diffusers for perforated ones.

Operators who are designing the restaurant from scratch can factor ventilation into the kitchen design, to develop an optimized exhaust system that saves money. They can place MUA diffusers far away from the hood. They can order a deeper hood with a bigger overhang, which is proven to capture more air than a shallower hood. And, they can install side panels at the same time as the hood. Playing around with the layout of kitchen appliances can help. It is more efficient to place heavy-duty appliances under the center of the hood rather than at the edge. Light-duty appliances can be placed near the edge.

If you have tried these steps already and are looking to increase your savings, consider what is known as demand-controlled kitchen ventilation, or DCKV. Traditional fan systems operate at a set speed regardless of the number of appliances in use. DCKV systems adjust the exhaust rate based on the number of appliances in use and amount of cooking. During a busy shift, the fan operates at 100 percent. When the cooking load is lighter, the fan operates at a lower speed.

Most DCKV systems have sensors installed at several points underneath the hood. These sensors detect smoke or measure appliance or duct temperatures to determine how fast to run the fan. Variable frequency drives ramp up or dial down the fan speed as needed.

Young compares the conventional hood design to running the heat in a home on full blast all day long. "You turn the switch and it runs full tilt whether you are cooking or not. It makes no sense," he says. Some operators wind up leaving their hood on all the time because they do not know how much it costs. DCKV considers the cook line, time of day, and level of cooking activity to operate the hood at the lowest level needed for proper ventilation. When only prep cooks are working, energy usage is minimal. During a shift when the cook line is in full swing, energy usage will be higher. Energy costs come down because you pay for only what is needed, rather than paying for 100 percent of output when less is needed.

DCKV can be retrofitted on existing hoods, but it is often expensive. Factor in the new installation, wiring, and variable speed fans, and the price point to retrofit often does not make sense, says Young. For this reason, he recommends DCVK for new installations. While DCKV is not ideal in every situation (Young mentions a concept with a large broiler as a primary cooking tool as one ill-suited to the technology), on average, it cuts hood energy usage in half.

Operators fortunate enough to live in a state that offers rebates can save money on energy-efficient improvements and see a return on investment sooner. California offers a rebate of $600 per horsepower for commercial kitchen upgrades, Young notes.

At present, rebates are available in the following states:

• California
• Illinois
• Indiana
• Massachusetts
• Michigan
• Nevada
• New Hampshire
• New York
• North Carolina
• Pennsylvania
• Rhode Island
• South Carolina
• Washington

"If your utility is not part of the Instant Rebates program, you may still qualify for other foodservice rebates so be sure to ask. These are public dollars specifically set aside to help operators design better kitchens," Young advises.

When restaurants use a lot of MUA, the cost of running hoods goes up. Finding ways to lower the cost of MUA can save money. In many cases, Young says, it can be more efficient to use air-conditioned air from the dining room as part of the MUA formula.

This may sound counter-intuitive to an operator, so Young illustrates with an example. Dining spaces often have fresh air requirements for customers so large that "surplus fresh air" is left over. If this extra air is not used as MUA, it gets recirculated and then removed to adhere to the fresh air guidelines.

"Instead of pushing the nice air out the roof, I let it transfer into my kitchen and be used as part of my MUA supply," Young explains. Chilled air that would otherwise be vented outside is instead used as MUA, reducing the size of the MUA unit needed for the kitchen.

When chilled air is used as MUA, it is known as transfer air. "Typically transfer air is a good technique because it is using already cooled and recirculated air and pumping it into a place that is hot and has not great MUA," Young adds. Transfer air would not work for concepts that lack dine-in space, such as a drive-thru only restaurant.

Survey Says

Operators might consider an energy survey to understand where there may be ventilation issues costing them extra money. Restaurant operators in Pacific Gas & Electric (PG&E) territory, which extends from northern California to Santa Barbara, can take advantage of a free energy sur- vey program run through PG&E.

SoCal Gas and Edison provide a similar service; however, their assessments may be less thorough, says Young. Operators in other states can download a do-it-yourself energy survey tool from the California Energy Wise website and run their own energy survey.

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California Energy Wise: Evaluating Current Equipment and Systems On-Site Energy Surveys

While a self-assessment will not be as robust, it can provide insight into energy leaks. Tackling leaks one at a time will help operators save energy and money. Return-on-investment calculators on the California Energy Wise website help operators understand the break-even point of investing in these improvements.