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Changing The Rules: Exhaust-Energy Limits

Times sure have changed for kitchen-exhaust regulations. Not all that long ago, safety and air quality were the only goals driving exhaust standards. The main idea was to ensure kitchen hoods could move a sufficient volume of air, so minimum rates were prescribed.

Numerous code bodies got involved in setting exhaust standards, which often but not always were based on numbers developed by the American Society of Heating, Refrigerating and Air-Conditioning Engineers. ANSI/ASHRAE Standard 154, “Ventilation for Commercial Cooking Operations,” for years has included, among other things, minimum exhaust rates for unlisted hoods. 

ASHRAE 90.1-2010 Sets Restrictions

The general state of affairs worked, more or less, and refinements in hood design and technology improved efficiencies. Underwriters Laboratories came along with UL 710, “Standard for Exhaust Hoods for Commercial Cooking Equipment.” UL 710 covers a multitude of criteria, including evaluating hoods for minimum exhaust flow required for capture and containment. ASHRAE 154 traditionally listed minimum cfm requirements to ensure “enough” airflow to capture and contain effluent. If a hood is tested against UL 710 and achieves capture and containment at a lower exhaust volume than the ASHRAE 154 minimum, it not only meets but exceeds ASHRAE 154 and is considered listed.

Fast forward to 2010, when a major update of ANSI/ASHRAE/IES Standard 90.1, “Energy Standard for Buildings Except Low-Rise Residential Buildings,” took effect. The updated regulation established several new requirements for kitchen exhaust in general as well as setting maximum exhaust rates specifically for kitchens with total exhaust of 5,000 cfm or more, thus changing the whole ball game. 

ASHRAE 90.1 gradually has built momentum over the past five years, and according to the U.S. Department of Energy, at last count 22 states plus the District of Columbia have adopted ASHRAE 90.1-2010 or higher energy standards for new construction. Existing buildings undergoing substantial renovations have to meet current state requirements. (In other words, they could be grandfathered or made to meet prevailing standards, depending on the state. You can see an updated list at energycodes.gov/adoption/states.) With four of the top five most populous states—California, Florida, Illinois and New York—already on board, more than a quarter of the market has switched to ASHRAE 90.1.

California, the most populous state with roughly 12% of the entire U.S. population, followed, with its updated Title 24, “Building Energy Efficiency Standards for Residential and Non-Residential Buildings,” effective Jan. 1, 2014. Title 24, as its name suggests, is comprehensive like ASHRAE 90.1, covering everything from windows and HVAC to lighting and more. Title 24’s latest version varies in some details, but where commercial kitchens are concerned, it essentially adopts ASHRAE 90.1’s kitchen exhaust requirements. 

Whether or not the new regulations are earthshaking depends on who and where you are. A lot of the major kitchen designers, especially those with projects on the West Coast, have been designing to higher efficiencies and lower exhaust rates for years anyway. Programs such as the U.S. Green Building Council’s Leadership in Energy & Environmental Design, California’s earlier Title 24 requirements and energy costs in general have raised awareness of energy efficiency and the role of lower exhaust rates.

“The new Title 24 probably is not a big deal for our office that I know of,” says Mike Dyekman, FCSI, Technical Manager at Webb Foodservice Design, Tustin, Calif. “Maybe it is at some other places, but we’ve always been on the front lines of mechanical engineering on these [hoods]. The thing that changed with Title 24 was that it [formalized] these requirements. 

“We always use engineered, listed hoods. We haven’t used a non-engineered hood since the early 1990s. Unlisted hoods just don’t do what we need them to do,” he says. Additionally, Webb designers have been incorporating all of the energy-reduction techniques available since they’ve been in business. “We couldn’t bring in untempered air, so the better design idea has been to remove as little air as possible,” which makes it easy to meet ASHRAE 90.1.

“We’ve been doing demand-controlled kitchen ventilation too, anyway, because of LEED. We probably have DCKV on 50% of our projects.” Dyekman says much of his work is in colleges, universities, K-12 schools and healthcare facilities. 

Min An, FCSI, Project Director at Ricca Design Studios’ San Diego office, echoes Dyekman and notes information coordination is important. “We get to work very early with mechanical engineers,” she says. “We coordinate early, so we don’t have addendums and cost overruns. If we don’t connect early on, we see more fans than needed installed or supply fans that don’t match what we specified. Communicating with the ME from the start helps avoid those issues.”

For others, though, the updated ASHRAE 90.1 has shaken the status quo. In the November 2014 issue of ASHRAE Journal, Don Fisher, Founder, and Rich Swierczyna, Senior Engineer at Fisher-Nickel Inc., which runs the Pacific Gas & Electric Food Service Technology Center, San Ramon, Calif., wrote an in-depth story laying out the changes and explaining their rationales. 

Among the key points:

Replacement Air Dos And Don’ts 

The first significant update for kitchen exhaust requirements appears in ASHRAE 90.1, Section 6.5.7.1.1: “Replacement air introduced directly into the hood cavity of kitchen exhaust hoods shall not exceed 10% of the hood exhaust airflow rate.”

This limitation applies to all kitchens regardless of exhaust volume, and, in effect, this is the end of the long disfavored short-cycle hoods. Back in the 1970s, short-cycle hood design was thought to be a way to save money by using untempered—not heated or cooled—replacement air. Introduced right within the hood canopy from outside, it didn’t render the kitchen too hot or too cold because it never entered the space. But hood engineers eventually realized replacement air delivered straight into the exhaust hood directly competed with the effluent plume draw. To ensure proper capture and containment of the effluent plume, the hood’s exhaust rate had to be turned up very high. Short-cycle hoods were never a good design and now, with ASHRAE 90.1, they’re not acceptable. 

Section 6.5.7.1.2: “Conditioned supply air delivered to any space with a kitchen hood shall not exceed the greater of:

a) the supply flow required to meet the space heating or cooling load.

b) the hood exhaust flow minus the available transfer air from adjacent spaces. Available transfer air is that portion of outdoor ventilation air not required to satisfy other exhaust needs, such as restrooms, and not required to maintain pressurization of adjacent spaces.”

Translation: Limit the amount of conditioned, dedicated supply air you have to introduce for your replacement air. You’ve already heated/cooled the air in other parts of the facility, so use it for transfer air where and when possible. Doing so may let you minimize the size/volume of a dedicated makeup-air unit. 

The question of the cost-effectiveness of using transfer air will come up in some cases. Will you need ducts and fans to move enough transfer air from spaces far from the kitchen? If so, run the numbers. In some instances, installing a dedicated makeup-air unit may be more cost effective than pushing transfer air toward the kitchen. If a dedicated makeup-air unit is the better choice for your operation, you’ll need to make your case to the budget department during the planning stages.

Max Exhaust Limits 

Section 6.5.7.1.3: “If a kitchen/dining facility has a total kitchen hood exhaust airflow rate greater than 5,000 cfm, then each hood shall have an exhaust rate that complies with Table 6.5.7.1.3. If a single hood is installed over appliances with different duty ratings, then the maximum allowable flow rate in each section of the hood shall not exceed the Table 6.5.7.1.3 values for the appliance duty ratings in that section of the hood. Refer to ASHRAE Standard 154-2003 for definitions of hood type, appliance duty and net exhaust flow rate.”

This is “The Big One” in the sense that it’s clear, there are now maximum caps on your exhaust rates. Note, though, that it applies only to kitchens with 5,000 cfm or more of total kitchen exhaust. Why the threshold? The cost/benefit analysis is pretty clear for larger installations, but not so much for smaller ones. The 5,000-cfm threshold means QSRs and smaller restaurants won’t need to comply. 

Are maximum exhaust rate limits attainable? Everyone we spoke with said yes. Note that the maximums caps are almost a third lower than the minimums prescribed in ANSI/ASHRAE 154 for unlisted hoods, so in effect, unlisted hoods now are out of the running. But generally speaking, UL-listed hoods can do their jobs and stay under the maximum exhaust limits. Not that you can take it for granted, though; specific applications make a difference. Some island hoods in open display-cooking stations will be challenged to stay below the maximum caps. Oversizing, overhangs and aerodynamic designs, such as air curtains, will make a difference. Designers will have to pay attention to matching hood specifications to particular cooklines and open areas.

One other caution: If you’re designing a bigger kitchen, keep in mind the language in Section 6.5.7.1.3. The limit refers to total kitchen hood exhaust as opposed to individual hood volume. There’s no gaming the system with multiple smaller hoods or sections. 

“There’s a lot of talk about the maximum limits in ASHRAE 90.1,” Fisher says. “But the heartburn is in the a, b, c options [see next Section 6.5.7.1.4] for choosing technologies—hitting transfer-air percentages, using DCKV systems or energy recovery.” Which approaches and/or devices do you need or want and which make the most financial sense? 

Required Techniques—Choose One Or More

Section 6.5.7.1.4: “If a kitchen/dining facility has a total kitchen hood exhaust airflow rate greater than 5,000 cfm then it shall have one of the following:

a) At least 50% of all replacement air is transfer air that would otherwise be exhausted.

b) Demand ventilation system(s) on at least 75% of the exhaust air. Such systems shall be capable of at least 50% reduction in exhaust and replacement air system airflow rates, including controls necessary to modulate airflow in response to appliance operation and to maintain full capture and containment of smoke, effluent and combustion products during cooking and idle.

c) Listed energy-recovery devices with a sensible heat-recovery effectiveness of not less than 40% on at least 50% of the total exhaust airflow.”

The first option—at least 50% of all replacement air being transfer air that otherwise would be exhausted—is self-explanatory and a cost-effective technique in some installations. But it won’t be cost-effective in all cases, Fisher explains, either because of the capital costs for ducting and fans or because of excessively high transfer-air velocities. Getting, say, 30% or 40% of your replacement air via transfer certainly is an incremental cost advantage, but it won’t qualify you for this section of the regulation. 

DCKV systems often will be the most cost-effective solution, according to everyone we checked with. Watch the specs carefully, though. Not all DCKV systems can decrease to 50% volume and still capture/contain at the idle rates of certain types of equipment. A charbroiler, for example, generates a lot of plume at idle; woks do, too.

The third option—energy-recovery devices—in principle is feasible, but because of a variety of complications, including regulations, the cost/benefit ratio in most cases won’t work. Energy-recovery devices are priced too high to be cost-effective in many cases, and some building codes don’t recognize them. 

Fourth Option In California

Interestingly, California’s Title 24 offers a fourth technique that can be selected as an option to ASHRAE 90.1’s three choices noted previously. Title 24, Section 140.9, “Prescriptive Requirements for Covered Processes,” (b)2.B.iv lets you opt for “a minimum of 75% of makeup-air volume that is:

a) Unheated or heated to no more than 60°F; and

b) Uncooled or cooled without the use of mechanical cooling.” 

Fisher notes this can be a viable choice in some installations, mainly temperate locations near the ocean. Especially in lower-humidity areas, Fisher says, evaporative/“swamp” cooling can be a viable and very cost-effective way to meet requirements. Otherwise, however, for much of California, untempered or barely tempered makeup air from a dedicated makeup-air unit would be too hot or too cold for a reasonable kitchen work environment.

All in all, as Fisher notes in his ASHRAE Journal article, a combination of techniques described in ASHRAE 90.1 someday could advance commercial kitchen ventilation to near-net-zero energy consumption. ASHRAE and the commercial kitchen ventilation industry have, he writes, “moved the North American CKV design world from the dark ages to the front-of-the-pack.”

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