HVAC Efficiency and Commissioning (a scary story)

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

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.