The notion that selecting the right hood and optimizing kitchen ventilation design can have a major impact on energy savings in commercial kitchen operations is nothing new. However, after decades of research and highly vocal education by engineers, the industry has finally responded with new technologies, standards, design improvements and best practices that make it easier and more affordable to reach higher levels of hood performance and efficiency than ever before.
In other words, the light at the end of the tunnel for ventilation has finally begun to show.
Ventilation systems represent an intricate web of stainless steel exhaust hoods, exhaust fans, makeup air units, grease removal apparatuses, fire suppression systems and controls. Throw in demand-controlled fans, infrared and temperature sensors, side panels, flanges and backwall supply, and things get even more complicated.
So it's no surprise that many operators have been so slow to adopt some of the more modern advances and technologies in the ventilation field. But things are beginning to change as energy costs and the pressure to reduce carbon emissions both continue to rise. As rebates, education and better technical support reduce the barriers to entry, more operators now embrace the benefits of energy-efficient ventilation systems. These systems demonstrate the highest level of capture with as little energy usage as possible.
Demand-Controlled Kitchen Ventilation
Demand-controlled kitchen ventilation (DCKV) has finally started to take off as operators realize the detrimental effects running the hood 24/7 can have on their energy bills.
"It's going to be the future of the industry," says Rich Swierczyna, senior engineer and commercial kitchen ventilation manager at Fisher-Nickel Inc., a San Ramon, Calif.-based division of Frontier Energy Inc. "While there is still a cost barrier for mom-and-pop restaurants, many hotels and institutions see great value in demand-controlled ventilation." Some larger chain restaurants also acknowledge the business case for the technology.
And, the return on investment — once on the slow side — continues to accelerate; DCKV systems can lead to energy savings of up to 60 percent. Analyze those systems in cities and regions with extreme weather swings like Chicago or Miami, and the savings only continue to climb, according to Swierczyna.
According to the EPA, manufacturers can increase the responsiveness of their systems through one of four methods: placing the temperature sensor closer to the cooking appliance; providing an optical sensor to detect effluent; using an infrared sensor to detect temperature changes remotely rather than waiting for the heat or effluent to waft up; and directly communicating with the cooking appliances.
In the past two years, the number of DCKV systems with multiple temperature sensors (for placement closer to the cooking appliances) and remote sensors has increased. That led to further energy savings in some installations with highly variable cooking loads, which allows for significantly decreased fan speeds during idle periods.
Integrating DCKV with energy management systems that can remotely monitor the system's operation can even more dramatically improve performance and energy savings, although hood manufacturers and EMS providers still seem to work independently of each other.
At least one hood manufacturer offers an integrated system, but many others remain in stand-alone operations, which poses an ongoing challenge to DCKV adoption in the market. "It's become a political issue, but we're hoping in the near future that these two technologies will be eventually integrated," says Swierczyna.
After seeing the benefits of an integrated EMS and ventilation system, Red Robin Gourmet Burgers and Brews continues to roll out new energy management systems across its 449 corporate-owned restaurants in the U.S. and Canada. The project is on track for completion by early 2017.
Energy management systems underwent significant testing in select Red Robin restaurants prior to the system-wide rollout that began in May 2016, according to a statement released by the chain. The end result will give Red Robin increased ability to control HVAC set points and exterior lighting, as well as monitor both HVAC and water heater performance and efficiency in its restaurants. The new systems will also provide Red Robin with visibility into HVAC unit performance and streamline the maintenance process.
In other positive news, the number of incentive programs and rebates for DCKV continue to grow. And, Swierczyna notes, "these incentives are slowly popping up outside of California across the country in 18 states and 2 provinces including Washington, Illinois, Wisconsin, Michigan, Pennsylvania, New York, Georgia, Texas and also in Canada, where more energy companies are getting involved and promoting DCKV."
New Standards for Commercial Kitchens
Some new standards for commercial kitchen ventilation have helped improve the capability and the case for adopting more energy-efficient technologies and models, including DCKV.
According to David Zabrowski, general manager at the PG&E Food Service Technology Center (PG&E FSTC), the ASTM Committee F26 on Food Service Equipment is working with the ASHRAE Standard Project Committee 154 (Ventilation for Commercial Cooking Operations) on commissioning a procedure for DCKV systems. ASHRAE 154 was recently updated to include heat load calculations for different types of hooded and unhooded commercial foodservice equipment based upon recently completed studies (Revised Heat Gain Rates from Typical Commercial Cooking Appliances from RP-1362 and Countertop Commercial Appliance Emissions from RP-1631).
The ASTM kitchen ventilation subcommittee F26.07 is reviewing the following standards: F2800 Specification for Recirculating Hood System for Cooking Appliances, F1704 Test Method for Capture and Containment Performance of Commercial Kitchen Exhaust Systems, and F2975 Test Method for Measuring the Field Performance for Commercial Kitchen Ventilation Systems.
The other major item was a recent adoption by UL of a revised requirement under UL 921, which requires the testing of ventless dishwashers in accordance with the requirements in ASTM F2474, Standard Test Method for Heat Gain to Space of Commercial Kitchen Ventilation/Appliance Systems. This requires testing in place of a previously used alternate calculation method, according to Zabrowski. ASTM, NAFEM and UL have formed a joint task group to explore the requirement more fully and to develop a test protocol and/or an acceptable alternate calculation method that effectively accounts for heat load to space for ventless dishwasher designs.
"Commissioning of demand-controlled systems will find its way into standards and codes pretty soon to ensure they are operating correctly after they are installed," says Swierczyna. Testing ensures these systems can still capture smoke when operating at high speed and then at lower speeds.
Designing and Configuring the Hood
While choosing more advanced hoods can help save energy, foodservice operators and designers have many design configurations to consider that will improve performance of any hood. It's also important to consider which equipment pieces fit with which hoods, and how much hood a foodservice operation actually needs in order to do more with less and make it easier to service the equipment. Research shows that specific construction features and installation configurations, as well as makeup air introduction, can all have a dramatic impact on the hood's ability to capture and contain smoke and grease. Manufacturers have responded by incorporating some of these features into new products.
"The shape of hoods are changing," Swierczyna says. "There are many new designs, including ones with multifaceted front edges to better streamline how the air is pulled into the hood and help them operate at lower air flow rates. Some hoods now attach to back walls to make sure the cooking plume gets to the filter easier." One manufacturer has added little air jets along the perimeter of the sides and front to extend the lower edge of the hood.
These designs are extensions of side and end panels that ventilation engineers have fought for years to include in standard hood specifications.
Side and end panels or skirts can dramatically reduce the exhaust rate of a wall, double-island or single-island canopy hood by improving capture of the replacement air drawn across the front of the equipment, according to the PG&E Food Service Technology Center. Testing has shown that these panels can encourage an energy reduction of 30 percent.
Engineers continue to encourage specification of side panels on kitchen exhaust hoods as standard, rather than best practice. Even very small side panels can improve exhaust hood performance, according to the PG&E FSTC.
In addition, many aerodynamic features have been integrated into the design of leading brands of listed hoods, including flanges or lips along the hood's lower edge, air jets, resized filters, eliminated filter shelves, wall-mounted canopy hoods, and backshelf, pass-over or eyebrow hoods that can be mounted at different heights and horizontal positions relative to the cooking equipment.
According to the PG&E FSTC's design guides, developed in part by Southern California Edison, a single-island canopy hood requires more exhaust than a wall-mounted canopy hood, and a wall-mounted canopy hood requires more exhaust than a proximity (backshelf) hood.
The fundamental steps in the design of a CKV system include: 1) establish location and "duty" classifications of appliances including menu effects, and determine preferred appliance layout for optimum exhaust ventilation; 2) select hood type, style, and features; 3) size exhaust airflow rate; and 4) select makeup air strategy, size airflow and layout diffusers.
Laboratory testing of different combinations of appliances has demonstrated that minimum capture and containment rates vary significantly due to appliance type and position under the hood. For example, a heavy-duty appliance at the end of a hood is more prone to spillage than the same appliance located in the middle of the hood.
Optimizing makeup air is another important factor in designing a hood installation for maximum performance and efficiency, according to a design guide published by the California Energy Commission and the PG&E FSTC. Use of air curtains, front-face air supply, backwall supply (rear discharge), perforated perimeter supply and four-way ceiling diffusers can all introduce makeup air in proper ways with the right implementation.
In addition, integrating kitchen exhaust systems with building HVAC units can also help operators achieve optimum performance and energy efficiency, as can optimizing the position of equipment underneath the hood. Overhang and rear gap are important parts of that determination. According to a fourth design guide published by the PG&E FSTC, an increase in overhang will significantly improve the ability of a wall-canopy hood to capture and contain cooking plume.
"Something as simple as pushing appliances to the back wall can save as much as 40 percent on air flow rate," says Swierczyna.
A large overhang is also beneficial for appliances that create plume surges when doors or lids are opened, such as convection and combination ovens, steam kettles, compartment steamers and pressure fryers. Specifying a deeper hood (for example, 5 feet versus 4 feet) will directly increase overhang, provided appliances are situated as far back as possible in the hood. This is an effective solution for the oven or combination oven and its "door-opening" challenge.
Other Emerging Technologies
Heat-recovery devices have started to appear on the horizon in the form of emerging commercial kitchen ventilation technologies beyond demand control.
Some manufacturers are testing systems that can actually grab heat released from the exhaust duct — not just from other appliances — which can then be used to preheat water for water heaters, according to Swierczyna.
Swierczyna and other engineers continue to test other systems that can preheat the air that comes into the restaurant or operation for makeup air heating. By recovering heat with copper tubes from a fryer flue, for example, and moving it to a coil in a makeup air unit and blowing outside air over the warm or hot copper tubes, it warms up the makeup air to prevent the gas or electric furnace from working as hard to maintain the thermostat's set point temperature.
A third heat-recovery technology captures the steam and plume released from dishwashers through a similar coil system. "Before you open the door, you would wait 30 seconds while cold water runs through the coil, picking up heat from that plume," Swierczyna says. "That water goes back and heats the cold water coming into the dishwasher so you're able to preheat that water without having to hook up directly to a hot water line anymore. By using all of that plume through a heat recovery system, you can go with a smaller hood or no hood at all in the dishroom."
Though ventless is becoming more popular in certain situations, there are still issues, according to Swierczyna. "In small spaces, ventless equipment can create an increase in heat and humidity," he says.
Depending on use, ventilation systems have an average lifespan of between 15 and 20 years, but there are a number of signs it might be time to replace them.
The most obvious sign is grease building up that can't be removed through professional cleaning. In addition, excessive airflow, caused by an outdated system or poor design, can hamper performance and increase HVAC costs.
Menu changes might also call for a new hood configuration — or even a downgrade — because certain foods release more smoke and grease than others.
To keep hoods in working order, professionally clean the hood and duct twice a year, and clean the grease filters and the capture area at least weekly, depending on the application, according to most manufacturer guidelines. Less efficient grease extractors will need cleaning more often.
Operators should also thoroughly clean the makeup air unit's aluminum mesh filters every six months and replace disposable makeup air filters monthly. Inspect the exhaust fan and belt biannually. And depending on local code requirements, inspect fire suppression systems at least twice a year.
Ventilation poses some of the greatest complexities, considerations and code requirements in commercial kitchens, but instead of stopping the conversation and movement toward greater efficiencies, it should inspire it.