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HVAC Efficiency and Commissioning (a scary story)

Roy R 0 Ratings 1 Discussions 0 Group posts

Posted by: Roy R // Engineer working on living a sustainable life

adding a timer to your exhaust fan

As part of a major renovation of a 100 year old building that houses 46 students we added per circuit electricity consumption monitoring.  A month after the building was re-occupied we noticed that the kitchen panel was consuming a lot of power.  Apparently when the cook came in in the morning he would turn on the exhaust fan.  Then when he left that afternoon he wouldn't bother to turn it off.  It was running 24 hours a day around 5 or 6 days a week.  And there is a makeup air unit which supplies conditioned air to the kitchen which turns on with the exhaust fan.  Together they consume about 3 kw for the air moving fan motors.  In the winter there is even more energy used to warm up the makeup air.  The fans alone are 3 kwh an hour, 72 kwh a day, 360 kwh per week, 18,720 kwh per year, around $3500 per year. That is more than 10% of the entire building's electricity use.  Pretty spooky.

We replaced the switch on the exhaust fan with a $20 spring loaded rotary timer switch.  Now when the cook comes in he turns the knob and the fan runs for a few hours then shuts off.  Power consumption is down about 75%. I think the payback period was around 2 days.

I recommend fine grained consumption metering/monitoring to anyone who is managing a big building.  You will find it pays for itself many times over.

SawHorse, Inc.
4 Ratings 13 Discussions 7 Group posts

SawHorse, Inc.

Running it for a few hours is good to help remove any particulates from the cooking process. The energy saved is not just the power for the fans, but also and conditioned air that escapes as well. Even though there is make-up air (assuming that is it local to the cooktop) expensive conditioned air can escape as well.

Allison Friedman Weston, MA, united-states 0 Ratings 99 Discussions 131 Group posts

Allison Friedman // Rate It Green Admin

Thanks for sharing. It's amazing (and indeed scary) to think about how much energy and money would have been wasted without the electricity consumption monitoring... and your sleuthing to figure out the cause. Did you or your team have an idea of the ROI on the per circuit electricity consumption monitoring? Didi it help solve other problems? Amazing how we're all learning that information really gives us the power to solve some big problems.


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