Today, my kids were doing a Hewitt problem, which asked them to estimate the cost of keeping a porch light on all of the time. They were surprised at the insignificance of the expense (keep in mind that I work in a private school), and I said that I had one word for them. A five-syllable word. It starts with RE…  then FRIG…  then ER…

So naturally, this became the day’s homework. How much does it cost to run your refrigerator for a month?

  • Here is the Hewitt lead-in:

“One deterrent to burglary is to leave your front porch light constantly on. If your fixture contains a 60-W bulb at 120V, and your local utility company sells energy at 10 cents per kilowatt-hour, how much will it cost to leave the light on for the entire month?”

  • And here is the homework prompt:

How much does it cost to run your refrigerator for a month? If you cannot find a current- or power-rating on the unit itself, you can look up your fridge (or something similar) here and look under “Specifications”.

Ask your parents for the electric bill. Determine the total cost per kWh that the power company charges.

The wild card is how long the unit is actually running — this can be from 20% to over 50% of the time, depending on the age and quality of the unit. Additionally, a refrigerator will cycle more in the summer than in the winter. You can park yourself near the fridge to do some homework and time how long it runs and how long it is quiet before it runs again, or you can punt and estimate.


Here’s my report on my fridge.

My Refrigerator

GE GBC12IAX

http://www.ajmadison.com/cgi-bin/ajmadison/GBC12IAX.html

  • To find the Power (rate of energy use or output)

  • To find how much my refrigerator runs each month
This is an estimate; I will time the cycle and update.  Estimating that the refrigerator is running 30% of the time…
  • To find how much energy my refrigerator uses each month (kW•h)

  • My BGE rate
  • To find the cost to run my fridge for a month
I am using 388.8 kW•h of energy at 12.5774 cents per kW•h.

It costs about 50 dollars each month for me to keep fresh food in the house!

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