Green Tip: Specifying Energy-Efficient Ventilation

Though ventilation may not seem that interesting a topic on the surface, this is precisely the area of the kitchen that has seen the most technological advancements in terms of energy efficiency and design.

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Although there have been many small, intricate improvements to the physical design of commercial kitchen hoods, adding up to some big utility cost savings, the overarching technologies have vastly improved in two areas that relate to energy efficiency: first, integration of the kitchen ventilation system with the appliances positioned underneath the hood, and, second, integration of the kitchen ventilation with the design of the space and the building's HVAC system.

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This is according to Don Fisher, co-owner of Fisher-Nickel Inc. and operator of the PG&E Food Service Technology Center in San Ramon, Calif. Much of the reason why the industry did not experience marked improvement in this area until just the last few years has to do with cost.

"Variable-speed exhaust, or demand-controlled ventilation as it's also called, is a concept that was introduced 15 years ago, but it wasn't embraced that quickly because of the cost factor," Fisher says. "Demand ventilation is finally here to stay, and we're going to see it used more and more."

A well-engineered hood system can save 30 percent to 40 percent more energy than standard models, according to Eric Norman, FCSI, vice president of MVP Services. "It doesn't have to be the most expensive system, but [select] a demand-control model where the manufacturer has at least taken some steps to lower airflows based upon what's underneath the hood," he says.

Integration with Hood Appliances Temperature-Sensing Demand Ventilation

When functioning well, demand ventilation works in perfect sync with the equipment underneath the hood. Foodservice operators can choose from a few different types of demand ventilation, including those units controlled by temperature or CO2 sensors, infrared technology or computers, according to Fisher.

When using temperature-sensing demand ventilation, the system adjusts the amount of air it removes in concert with the level of cooking occurring underneath the hood. While growing in popularity, it's still not a perfect system, Fisher says. "There's a lag — if you put a burger on the broiler, the temperature often won't change fast enough for the hood to notice food is cooking."

Infrared-Sensor Demand Ventilation

Though typically more expensive than other options, infrared-sensor demand ventilation is one step up from temperature-controlled ventilation. "Infrared sensors can actually 'see' the smoke or steam being generated by a cooking process," Fisher says. Universities, healthcare facilities, institutions and large chains with big budgets and more energy to preserve tend to be the predominant consumers of this technology.

"Running a variable speed is technically a no-brainer, but the hurdles are the costs associated with more advanced models," Fisher says.

Still, according to Norman, payback can happen quickly with energy-efficient hood investments. "Even with the cost of a high-end ventilation system, the return on investment is very quick," he says. "If you have a hotel and you're running your hood for 18 hours a day, think of the costs associated with that."

Foodservice operators can recoup the money they spend on purchasing demand ventilation systems thanks to the savings they could realize on the amount of treated air not having to be exhausted constantly. "A return on investment could happen in as fast as 12 to 16 months, and then the hood will last another 10 years," says Norman. "After the initial return, now you're saving money every day because of that high-end system you put in."

Hoods and Kitchen Design

Positioning equipment underneath the hood in a strategic manner can also help improve energy efficiency, according to Norman. "For instance, using one piece of equipment like a combi oven can take the place of two other pieces and lower the linear cost of the hood, sometimes by at least three feet," he says. "At $1,400 per linear foot, that cost can really add up quick. It also reduces the amount of treated air being exhausted out of the space." Reducing hood size is just as important a consideration as selecting the right hoods when improving energy efficiency in ventilation, Norman adds.

Many operators opt for proximity hoods as opposed to the basic canopy-style hoods, Fisher says. Proximity hoods, also called backshelf hoods, hang lower over the cooking equipment unlike traditional wall-canopy hoods, allowing for lower exhaust flow rates and a physically smaller hood.

"As people try to squeeze more energy savings out of the kitchen, they're designing a hood for a given piece of equipment or series, like a fryer battery," Fisher says.

Proximity hoods allow for more flexibility in their design as it relates to the equipment underneath. Some new models act like a hybrid between a proximity and canopy hood: They mount to the wall but extend lower over the appliance to capture more air.

Selecting More Efficient Appliances

In addition to selecting energy-efficient hood systems, selecting energy-efficient equipment to function in tandem will help the hood work to its optimum energy efficiency level, Fisher says.

For example, California legislators have been considering a new rule that would increase the stringency of the requirements for grease removal and smoke control, according to Fisher. That means a forced change out of under-fired charbroilers.

According to research by the University of California, under-fired charbroilers account for 82 percent of pollutants generated by restaurants. The focus of proposed rules for newly installed under-fired charbroilers would be to reduce emissions from high-production restaurants using this equipment, either by requiring an expansion of the grill surface area or the use of certain — certified — hoods.

In some cases, Fisher says, it would be less expensive for a restaurant to purchase a more efficient griddle than to replace or expand upon a costly hood system, or possibly purchase a specific, certified model required by the state. "That equipment is expensive, and it's not been perfected yet," Fisher says. "It could be easier to change the griddle and to change the process a little to control the smoke."

Smart Kitchen Technology

One step further, high-tech demand ventilation and hood technology work in perfect sync with a computer system monitoring the kitchen 24/7.

Norman's team installed a smart kitchen technology system at Kendall College in Chicago during a major renovation of the main dining room's kitchen. "I can log on the website, and see in real time what hoods are on, what speed they're at, what equipment is underneath them, and how hard that equipment is working from any remote computer at any time of day," Norman says. "There's even a screen on the wall where we put the real-time data showing the hood system and how it is running compared to a conventional hood system to demonstrate the energy savings to the students."

While the hoods themselves use a mixture of temperature and infrared sensors, the ability to monitor the system helps the operator add another layer of control in case there is a misreading of the equipment. "If it's five in the morning and you're baking something, the hood will run at minimal speed because only one piece is running and the whole kitchen doesn't need to be exhausted," Norman says. "That right there is huge in energy efficiency because the system is [operating] based on what's running underneath the hood rather than running on full blast."

Integration with the Building Makeup Air

Aside from improvements to the actual hood structures themselves and positioning of the equipment underneath, designers are also increasingly looking to integrate hood technology with the rest of the building's HVAC system, according to Fisher. What started among LEED projects has trickled into basic, good hood design.

These systems use fresh outdoor air twice, once in the dining room and then bringing that treated air into the kitchen as a contribution to makeup air, Fisher explains. "That allows you to significantly downsize the dedicated makeup air in the kitchen. Instead of a 6,000 cfm exhaust system, we can make that a 4,000 cfm system by using proximity hoods, and then go one step further to take 2,000 cfm of the air from the dining room as transfer air."

A good makeup air system can lower energy costs by as much as 35 percent, adds Norman. "The balance between makeup air and exhaust hood is very important."

Heat Recovery Technology

A newer technology, heat-recovery systems are just beginning to gain some traction in the industry, Fisher says. The potential to take heat out of exhaust air and use it to preheat incoming air is just another way to improve the efficiency of kitchen ventilation. "Believe it or not, one manufacturer had a similar system, they called an air-to-air heat exchange 10 years ago, but it didn't catch on."

Just last year at the National Restaurant Association show, Fisher says, he saw the technology being introduced in the marketplace again. What started in the dishroom is making its way over to the cookline. It's also another example of improving integration between hoods and the surrounding environment.

"A lot of the energy-intensive heat in foodservice is thrown out," Fisher says. "Kitchens of the future will have ways to capture wasted energy streams. I see more of the heat recovery happening with dishwashers moving into kitchen ventilation in the next few years."

Ventless Design

Ventless cooking remains a gray area, in Fisher's opinion. Conventional ventilation, compared to ventless setups, is not all that expensive, he says. "With a ventless hood, 100 percent of the heat is put into the surrounding space, and unless you're using recirculating hood systems like in stadiums or arenas, they don't always work effectively," he says. A ventless setup in a stadium might be a viable solution as opposed to working in 50 feet of ductwork, but this doesn't always translate to other kitchen and foodservice production setups.

Making Ventilation a Priority

Kitchen ventilation works in extremes: The worse the system is, the worse the energy drainage you'll have; the better the system, the better your energy efficiency — and these differences in efficiency are significant. The trick is to select the right hood for the budget, cooking capacity and ventilation needs, making sure the system is carefully integrated and aligned with both the equipment underneath it and the surrounding environment, including the building's HVAC system.

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