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How to calculate usage of a refrigerator?

  1. Jul 29, 2010 #1

    I have a refrigerator (model No FRT18SJGW1) which consists of a freezer compartment on the top and a bigger frige compartment below. It is operating 24 hours a day and 365 days a year.

    There is a label in its fridge compartment saying:
    Electrial ratings: Amps 4.75, Volts 115, Hertz 60

    I tried to compute its energy usage per year, and here is my computation:
    4.75 Amps * 115 Volts * 0.001 * 24 hrs * 365 days = 4785.15 kWh/year

    I looked up its model No FRT18SJG*1 (FRT18SJGW1) on http://www.energystar.gov/index.cfm?fuseaction=refrig.calculator, and found that it uses 766 kWh/year

    Although I know both my computation and the website are estimates, they are too far different. What has been wrong? How can I do the calculation correctly?

    Thanks and regards!
  2. jcsd
  3. Jul 29, 2010 #2
    refrigerator's compressor does not work whole time. the operation is intermittent, it goes off when desired temperature is reached. say compressor is on for 20% time your estimate would be 4785*0.2 = 957 KWH/Year
  4. Jul 29, 2010 #3


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    How old is this refrigerator? I've seen them where water has been absorbed in the insulation and their compressor do run most of the time.
  5. Jul 29, 2010 #4
    Manufactured in 1998. Believed to have been used most of time since. Given by my landlord.

    I was also wondering what the refrigerator's power should be like after being used for 12 years, and if the amount 766 kWh/year shown at energystar website has taken into account the age of the refrigerator?


    Last edited: Jul 29, 2010
  6. Jul 29, 2010 #5

    Where to get some basic sense of how much the rate for the compressor is?

  7. Jul 29, 2010 #6


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    You can buy 'smart meters' these days which will measure the energy consumed by a device of a whole house. Unlike the rotating disc type, they aren't very expensive and would be very informative on many occasions.
    I have often considered buying one for myself but the idea has never reached 'critical mass' - so I haven't bought one yet.
  8. Jul 29, 2010 #7
    it depends on usage, initial temperature of objects being kept in refrigerator, frequency of opening door etc.

    20% is fair operation time in normal conditions.
  9. Aug 19, 2010 #8
    Honestly speaking, I don't know how to calculate the usage of a refrigerator. But on my own experience, if we want to calculate our usage of our refrigerator, we contact our refrigerator's manufacturer. Then we notify the customer representative that we wish to calculate a refrigerator's annual kWh. Then they will assist you!
  10. Aug 20, 2010 #9


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    There are so many other factors involved. Where the fridge is sited, how freely the air flows around the heat exchanger, ambient temperature, the temperature you want the cabinet to have. Measuring it is the only way to have a better idea than that of the manufacturer's estimate. The card that each device is issued with (the coloured A,B,C,D etc.) with the energy consumption rating will give you a clue.
  11. Aug 20, 2010 #10


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    Staff: Mentor

    AKS pulled 20% out of the air, but it proved to be a fair estimate. Where you get the actual fraction is to run that calculation backwards. The fridge manufacturer has already taken all the necessary measurements to get their yearly usage and the utilization fraction is in there.
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