Under The Radar: Plug Loads


Chances are good that if you’re a multiunit spec/buyer these days, you put a fair amount of effort into energy efficiency. You probably give a lot of thought to the big cooking equipment, refrigeration, holding, HVAC, lighting, etc. Some of you have even won awards for your sustainability efforts (Arby’s comes to mind with its Efficiency Matters program, which reduced energy consumption 20% systemside), not to mention winning rebates, payback and profits.

So now that the big pieces are accounted for, what’s next? The smaller pieces, the plug-in kitchen appliances that by themselves might not use a ton of energy, but in aggregate become a big issue.

To get a grip on that topic, the California Energy Commission in 2015 released a bid for a project to define and measure plug load and then come up with priorities and strategies for reducing it. January ’16, Frontier Energy, which operates PG&E’s Food Service Technology Center in San Ramon, Calif., was awarded the contract. Work began in earnest in May, with David Zabrowski heading the effort as project manager and Mark Finck as principal investigator, working with fellow Frontier team members Edward Ruan and Denis Livvchak. Also on the project team are Don Fisher at Fisher Consultants, along with support functions from Opinion Dynamics and ADM Associates.

The project is scheduled for completion in March ’20, so the team is roughly halfway through now, and already valuable results are emerging.

For purposes of the project, plug loads to be studied are the ones generated by unventilated electric countertop equipment—toasters, soup warmers, panini presses, shelf heaters, coffee brewers, etc.

In all, based on operator survey data, a total of 14 countertop appliance categories have turned up (notably excluding microwaves because they’re either on or off—no ramp up, no idling, no variables). Some of the 14 obviously use more energy than others, and the first objective is to assess the energy load and energy reduction potential of each, characterize usage through field monitoring at a cross-section of different commercial kitchens in Northern California, and demonstrate reduced energy consumption through the use of emerging appliance designs and control technologies (smart and other technologies), and behavior/operation changes. The idea is to find ways to cut energy use during periods of minimal activity without compromising overall kitchen productivity.

As of early this year, the number of fi eld locations being monitored was about 12—including a large bakery/café chain location, university dining, hotel restaurant and a cafeteria, fine-dining, fast-casual, take-out and cafés. By April, the number had grown to 16 including three different QSR concepts and some other additions, and more sites are likely coming in the future. At each, kitchen countertop appliances are being individually metered, with usage and energy measured, data normalized and baselines established. The number of appliances per location varies by size and type of operation, but many sites have 10-15 such pieces.

Findings So Far
Among the interesting bits:
• Conveyor toasters, coffee brewers, espresso machines, rice cookers, and soup wells so far are the most commonly metered appliances.
• The most energy intensive appliances observed are conveyor toasters.
• Appliance energy usage varies significantly by site and operation type, with hours of operation and appliance settings playing a key role.
• Rice cookers, soup wells, and tea brewers used the least energy due to lower hours of operation and lower average input rates.

Conveyor Toasters—Conventional Vs. Smart
Conveyor toasters quickly showed they’re big on energy. They’re also big on potential for energy saving. Four conveyor toasters monitored at this point have fairly high usage—9.6 hr./day, with the highest average normalized energy usage rate of the 13 appliance categories metered so far at 2.22kW.

At one chain bakery/café, with the conveyor toaster operating from 4:30 a.m.-10 p.m. (with a half-hour late afternoon lull) energy consumption worked out to $2,900/yr. at $0.15/kWh. For perspective, note at a less busy college café, the conveyor toaster ran up $585/yr. in energy.

The good news: A “smart” conveyor toaster brings those numbers way down. A smart unit with a built-in sensor automatically activates the set toast cycle when a product is placed on the conveyor. Meanwhile, a color-sensing system monitors and adjusts conveyor speed and temperature to toast food consistently, and a power-saver mode automatically kicks on after a set amount of idle time. The net effect: In field metering, the combined effects of those smart attributes brought that $2,900/yr. annual energy consumption figure down by a full $1,000! Multiply that by however many conveyor toasters you’re running.

Soup Warmers—Conventional Vs. Induction
Down the list on energy consumption are soup warmers. They don’t take a lot of energy, but there are lots of them out there, and anyone doing soup likely has multiple warmers going. Energy metering of four baseline soup warmers and five induction soup warmers showed that induction units used 64% less energy than their conventional wet-well counterparts. At one of the café test sites, replacement of a single baseline soup warmer with an induction warmer yielded 52% energy savings—annual energy cost dropped to $22.41 from $46.25 for that one warmer.

But Wait, There’s More
As the project moves forward, more and more will be learned, and FER will cover the progress. Already the field data shows huge savings from induction hot plates vs. conventional, for example. Heat strips and heated shelves are using huge amounts of energy and are aching for optical or weight sensors to reduce heating empty spaces. Likewise, coffee and espresso machines would stand to gain efficiencies with simple techniques such as adding timers.

Not every category uses enough energy to justify technology upgrades, but many do. One thing is for sure—countertop plug load is a new frontier in energy conservation. 



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