FOCUS: Cutting Ventilation Energy

Everybody knows the heat is on for cutting utility consumption. But where to start? Who submeters everything? For that matter, who sees the utility bills? 

Exact numbers vary depending on whose chart you’re looking at, but most sources will tell you cooking/prep is the biggie, accounting for about a third of all energy at a typical foodservice facility. Next up, only a few points behind, is HVAC at 25% to 30%. Charts that separate heating, ventilation and cooling put ventilation at approximately 10%. This means hood exhaust, makeup air and tempering account for a very big chunk of your utility bill. It makes you wonder why you’re running your exhaust fan full tilt all the time even when there’s little or nothing cooking.

DCV’s Happy Chain Reaction

Demand control ventilation (DCV), either new or retrofit, can fix that. In simplest terms, DCV uses one or more types of sensors (all systems use temperature sensors, and some add optical to detect smoke/steam) with software, controllers and variable-speed fan drives to modulate exhaust- and makeup-air fan speeds. The fans speed up as cooking activity rises and slow down as it subsides. 

Reducing exhaust-fan speed is just the beginning of a happy chain reaction. As fan speed is reduced, fan energy is reduced by roughly twice as much. So, a 25% reduction in fan speed, which is a realistic average, results in energy reduction of more than 50%. And when you cut exhaust volume, you cut makeup-air volume, too, which means there’s another fan doing less work. Not to mention the heating and cooling of that air, which is where even more savings kick in.

“Heating and cooling energy for makeup air can be much more important than just the exhaust-fan energy or makeup-air fan energy, especially in harsher climates,” says Jay Parikh, founder of Compliance Solutions International and a consulting engineer who worked 26 years at Underwriters Laboratories, much of that time in kitchen ventilation. “You can expect to save 25% to 30% of HVAC energy” with DCV. 

Not to put too fine a point on it, but for ballpark estimates: If you could save 25% of HVAC energy, and if HVAC is 30% of your total energy usage, you’re talking about cutting around 8% of your total energy consumption. That’s a big pile of dollars, a pile that will only get bigger as energy pricing goes up.

Measuring Payback

So the upside is big. But what’s the capital investment and payback time? A simple answer would be handy but misleading. Size of operation, hours of operation and type of cooking all make a big difference, and different DCV systems have significantly different price tags. So the math can be all over the place. That said, most operators who are deciding to buy DCVs, whether for new construction or for retrofit, run the numbers and pick a package that’s giving a payback of less than three years, or often, less than two, according to manufacturers. “If I were an operator, I would think three or less is attractive,” Parikh says. “Less than two years, I’d be very much interested.” 

For illustration, Parikh notes a DCV control package for a retrofit for a relatively small kitchen with two hoods and one supply and exhaust fan, depending on particulars, could run less than $5,000 but commonly ranges from $10,000 to $15,000. For a larger kitchen, those figures increase. So payback matters, and in this category, payback also is directly tied to use. The more you’re cooking and the more time you can reduce fan speed and airflow volume in between cooking loads, the quicker your payback.

In “Future of DCV For Commercial Kitchens,” an article published in the February 2013 issue of ASHRAE Journal, authors Don Fisher, Rich Swierczyna and Angelo Karas of Fisher-Nickel inc. and the Pacific Gas & Electric Company’s Food Service Technology Center note “… the authors believe that any DCV is better than no DCV,” but they do acknowledge there are projects where DCV is not going to be cost-effective for either thermal or thermal/optical systems. 

Several manufacturers acknowledge large operations, such as casinos, hospitals and universities, clearly are prime candidates, and other makers have come to market with different systems that make DCV realistic for the broader market as well. Still, small kitchens, limited operating hours and small volumes are less likely to get a worthwhile payback.

Choices, Choices

In the beginning, there was one choice—yes or no. In 1987, a young Steve Melink started a ventilation testing and balancing service company for the restaurant industry. “I had an ‘aha!’ moment up on a roof,” Melink remembers. “A hood was blowing out air-conditioned air, and next to it an HVAC unit was working hard. So I started thinking, what are the main loads a smart hood should detect? Heat from appliances and smoke.” 

So he set to work developing a high-performance system that incorporated both temperature sensors and optical smoke sensors. That was the beginning of the Melink Intelli-Hood DCV system.

Over the past couple decades the system has continued to evolve. Software has become more sophisticated. Sensors are more sensitive and quicker to respond. Melink Corp., which still concentrates on the Intelli-Hood system and testing/balancing services—and doesn’t manufacture hoods—does about 90% of its DCV business in retrofits, Melink figures. “We prefer retrofits because we control the quality,” he says. 

Melink also sells systems to/through hood manufacturers, and the Melink system is modular, as Melink himself emphasizes, so if you don’t need optical sensors, for example, you can get a Melink system without them.

Until about 2000, the DCV market developed slowly. The concept was unfamiliar, so the market was slow to respond, and a single supplier could only cover so much ground. Also, for many years, codes such as the Int’l. Mechanical Code and National Fire Protection Association (NFPA) 96, Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations, required a minimum 1,500 fpm exhaust velocity. So even if you could drop below that level during light cooking times, the advantage couldn’t be fully exercised. It took an ASHRAE research project in 2000 to nudge code officials for revisions, and that’s when the market began to move. Now, further nudging comes with rebates that run $350 to $750 or more per horsepower and can cut system prices by perhaps 15% for a smaller project up to 30% for a larger one. Which of course shortens payback. 

During the past several years, as hoods themselves have become more efficient, nine more manufacturers have thrown their hats into the DCV ring. Between market economics and evolving technologies, the big drive has been to find simpler, most cost-efficient ways to reduce exhaust/makeup-air volumes while still meeting capture and containment needs.

As always, it’s a balancing act of what you need and what you want to invest. Does your menu generate a lot of smoke/steam, which often tends to increase more quickly than temperature? If so, you might want the quick-response advantages of optic sensors. On the other hand, supporters of thermal sensors say they’re more responsive now than in years past. So what do you need? Consider where the sensors will be, too, and how many you’ll need. The farther they are from the cooking area, the longer the response time. And the more there are, the more flexibility you can work into the system. The full matrix of considerations is too long to list here, but you get the idea. Different approaches work for different operators.

As we mentioned, several kitchen ventilation system providers originally dipped toes into the DCV pool with the Melink, but now are either developing or have developed proprietary systems. Others developed their own DCV systems from the get go. We’ve included system information from 10 companies including Melink in the DCV Gallery that follows and each entry has a link to company websites. 

The New Standard

Which types of DCV systems offer the best performance and/or the best payback remains to be seen as standardized testing continues. But as Fisher, Swierczyna and Karas assert in their ASHRAE Journal article, it’s clear that any DCV is better than none, and the only other major questions are payback period and evolving sophistication. DCV has been established as a “best practice” for several years now, and it now appears on the verge of becoming standard practice.

For more information on the ASHRAE article, search online for “Future of DCV For Commercial Kitchens,” or for case studies, check out fishnick.com/ventilation/demandventilation. “””