1-Wire Energy Management Projects

Home Telemetry and Control Systems to Monitor and Reduce Energy Costs

  My Refrigerator Story

Updated 02.20.11 with electrical bill information the month after we installed the new frig.

During the Christmas holidays (2010) I decided to embark on my next phase of home energy management by looking into the cost savings of shutting down my two refrigerators at night (like 11p to 6a). An easy task for my home control system. One refrigerator is in the kitchen and one in the garage.

We bought our kitchen frig about 5 years earlier (used) from a family moving out of the country and they said it had been a reliable working machine and willing to sell it for $150. Nice looking, 26 cubic feet, double doors and all.

Most new homes built since the '60s have separate breakers in the fuse box for all major appliances so using a clamp-on-amp meter, I checked the amps of both systems running.

  • Kitchen frig pulled 6.5 amps running and it's exactly what it says on the name plate (where the model number is identified).
  • Garage frig pulled .65 amps but it's smaller and newer

Next I would need to know normal cycle times it's on and off since if the frig is off more than half the time normally then it probably would not make much sense to turn it off the additional 3.5 hours at night since the saving would be small.

In some simple observation monitoring on a Saturday afternoon I couldn't tell if the frig ever turned off so I thought this would be a perfect use for my home telemetry system. (I already monitor both my home HVAC systems and have a few unused I/O channels) Only issue was "How do I connect the refrigerator to my home telemetry system?"  Hmmm...

First thing that came to mind was use a 120V AC controlled relay, similar to the way I monitor my HVAC systems (but on the HVAC I use a 24 VAC relay), but that would take wiring all the way to my frig in the kitchen and that would be next to impossible (since it's against an outside wall which has insulation and such).

My second idea was to monitor the current used by the frig at the fuse box. I can run some Ethernet cable to that box easily up to the attic where my telemetry and control system is but I need some way to monitor the current like a clamp-on-amp meter does.

Well clamp-on-amp meters use a "current transducer" to monitor the AC current flowing through a wire and transforms it into DC voltage.  It's exactly the same concept on how a power transformer works. Ok, so I whipped out my trusty AutomationDirect.com catalog and found exactly what I needed. $80 later along with some tricky electronics magic I was monitoring my kitchen refrigerator from the fuse box.

WOW! A few days later, looking over the telemetry data, my kitchen frigs runs 75% of the time! Then running through the math to figure out my electric costs:

  • 6.5 amps X 120 volts = 780 watts per hour
  • 780 / 1000 = .78 kilowatts (you pay for electricity in kilowatts)
  • Running 75% of the time then produces .78 X .75 = .585 kilowatts/hr

I paid 11.8 cents a kilowatt back then, I pay 8.9 cents today.

So each hour I paid  .118 X .585 = .069 dollars or 6.9 cents an hour

Ok, no big deal.

  • Each day I pay .069 * 24 hours = $1.66 - WHOA! That can't be good.
  • In a month I pay $1.66 * 30 = $49.80 - oh no!
  • In a year this frig cost me $49.80 * 12 = $597.60 = OMG!

So I checked my math over and over again and kept getting the same answer!

A 26 cubic foot frig sold today uses $50 in electricity a year!

Honey... I think it's time to buy a new refrigerator!

A little history on our old refrigerator: It was 28 years old and the bottom door gaskets were shot so cold air was leaking out the bottom of the doors. (who looks at the bottom door gaskets?) But also 30 years ago electricity was 4 cents a kilowatt!

We now have a new Samsung  RF266 refrigerator and it's hooked to my telemetry system and the numbers are right on with the electricity usage. The money I'm saving in electricity is paying for the frig!

How old is your refrigerator?

Update on 02.20.11

We just received our latest electrical bill. We have averaged about $163 over the last three months (not including the most recent bill). This time of year our electricity bill is always low since we have gas heating.

The most recent electric bill after we installed the new frig was $111! That's a $52 savings for one month!  My calculations were all correct!