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Ask the Expert: How to Determine if an Energy Management System is Right for You

As the Design and Product Specialist for Ventilation here at Unified Brands, one of the most frequently asked questions I receive is, “When would you use an Energy Management System (EMS) instead of an energy efficient hood?”

And like everything else in food service: it depends.

An elementary school that only cooks from 9 a.m. to noon to only serve lunch? It doesn’t really make sense. A full-service restaurant with more than one mealtime per day?  That’s the sweet spot.

In order for an EMS to save energy (and money), you need slow times in the kitchen – when the cooking equipment is on, but you aren’t actively cooking anything. That includes prep time before the first meal, downtime at the end of the day for cleaning, and lulls between meal periods.

These are called “idle times,” because the fans can operate at an idle speed.

First, I think it’s important to differentiate types of EMS, because they are definitely not all the same.  There are generically two different styles of systems: heat only and heat with a secondary sensor.

Heat Only Systems

Heat only systems generally have an idle speed of 80% of capacity. Some claim lower, but it’s dependent on the type of cooking equipment. That’s because it’s only reading heat, and not steam/smoke.

Because you cook cold product (i.e., frozen French fries, cold meat, etc.), the temperature of the air in the hood actually decreases when you start cooking, which is counterintuitive to how a heat only system works. This initial drop in temperature when you start cooking is also when the first puff of steam or smoke occurs. In order to ensure capture, the idle speed is higher to catch plumes of steam, smoke, or grease.

Heat with a Secondary Sensor Systems

The secondary sensor is usually optical, but as you can guess, optic sensors in a grease hood can be problematic – unless you use Avtec’s EcoAzur System, where the blue emitter and receivers are sealed behind a plastic lens, in a milled stainless probe.

When you add optics, like with the EcoAzur System, you add another layer of savings and protection. Our idle speed is typically 40% of capacity and will rise to 80% as the cooking temperature increases. The system only jumps to 100% when something (grease/steam/smoke) breaks the optic beam.

Taking a Look at the Math

Now that we know the different types of systems, let’s look at an example. To make the math easy, I’ll use a 10-foot hood for reference with mixed-use cooking equipment and we’ll size a generic box hood at 250 CFM per linear foot of hood which would give an exhaust of 2,500 CFM (250 CFM x 10-foot hood).

Okay, easy enough.

Let’s try this example: it’s a restaurant with service for lunch and dinner, where the kitchen equipment is turned on from 10 a.m. to 10 p.m., serving food from 11 a.m. till 9 p.m. Of the 12 hours the kitchen equipment is on, we’ll say 50% of the time is at idle.

(Remember: CFM is Cubic Foot per Minute, so you need to multiply by 60 to get Cubic Foot per Hour, and then multiply by the number of hours running.)

Box Hood Operation (Heat Only – Without Optics)

900,000 Cubic feet of air – 6 hours full speed

720,000 Cubic feet of air – 6 hours 80% idle speed

Total: 1,620,000 Cubic feet of air per day

Box Hood Operation (Heat – With Optics)

900,000 Cubic feet of air – 6 hours full speed

360,000 Cubic feet of air – 6 hours 40% idle speed

Total: 1,260,000 Cubic feet of air per day

What Does All This Math Mean?

Unsurprisingly, it’s far more efficient to run the hood with Optics added than heat only by around 25%.  Let’s now compare these numbers against the EcoArch Energy Efficient hood from Avtec.

For the same mixed-use kitchen equipment, our 10-foot EcoArch hood would be designed for 175 CFM per foot, or 1,750 CFM for the entire piece. Since we’re using standard on/off controls for this example, that would be 1,750 CFM for every minute the hood is running. Don’t forget: CFM is per Minute, and we need to multiply by 60 to get Cubic Foot per Hour.  We’ll also show the box hood with its EMS air flows from our previous examples for comparison.

EcoArch Energy Efficient Hood (Standard On/Off Controls)

1,750 x 60 minutes x 12 hours

1,260,000 Cubic feet of air for a 12-hour period

Box Hood Operation (Heat Only – Without Optics)

1,620,000 Cubic feet of air for a 12-hour period

Box Hood Operation (Heat – With Optics)

1,260,000 Cubic feet of air for a 12-hour period

As far as air flow, it’s more efficient to use the EcoArch hood with standard controls versus a box hood with heat only energy management. If you use an EMS with the addition of optics like Avtec’s EcoAzur, the CFM levels are going to be approximately the same as an EcoArch hood.  Of course, this is an example, and the real world rarely fits in a neat little box, but it’s the comparison between each that really shows the difference. The averages of savings may vary some, but the percentages of savings between each other will be very similar.

Benefits of Avtec Solutions in Your Commercial Kitchen

Having an EcoAzur system also adds additional layers of savings and protection with the system adjusting automatically for the human factor as well. If cooking equipment is accidentally left on – the hood isn’t turned off at the end of the night, for example – or an unusually slow meal period occurs, these Energy Management Systems match the exhaust to the cooking and save your energy and money.

Even though we didn’t discuss this in the example, we shouldn’t forget that you could bundle the EcoAzur Energy Management System with the EcoArch Energy Efficient Hood and have one of the most energy conscious easily maintainable systems available on the market today!

If you’d like to know more if an EMS is right for your situation, I’d love to talk with you so please feel free to reach out.

Jefferson Kenney
Design & Product Specialist – Ventilation
Unified Brands – Avtec
800-621-8560 EXT 6492

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