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B KWh versus kW times Time

  1. Mar 16, 2017 #1
    Say I have a 60W device.

    I know running for one hour it uses 60 W x 3600 s = 216 kJ of energy.

    Does that mean it uses 216 kWh of energy?

    Or does kWh means 60 W x 1 hour = 60 kWh?

    I am confused because the units in 60 kWh is not in their simplified terms.

    More specifically, this pertains to a project that I am working on.
    From experimental values, I found that with X kg/s of water flowing through the heat exchanger and some temperature increase, I can find the power of the heat exchanger in kW.
    I would like to provide the values in BTU since that is just what people still use in the States.
    I realized BTU is an energy unit, not power, and 1 kWh = 3412 BTU.
    So I need to convert kW to kWh.
  2. jcsd
  3. Mar 16, 2017 #2


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    you have a k in there that you shouldn't

    60 W x 1 hour = 60 Wh

    so going from what I wrote above

    a 1kW heater running for 1 hour = 1kWh
  4. Mar 16, 2017 #3
    Alright, thanks! I thought kWh is basically kJ. I guess kWh needs to convert by a factor of 3600 before it becomes kJ then.
  5. Mar 16, 2017 #4


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    Yes that's possible/correct.

    I believe they actually use BTU/h (BTU per hour) but the "h" is sometimes omitted (bad practice).

    So you just need to use..

    1 kW = 3412 BTU/hr
  6. Mar 17, 2017 #5
    One thing worth remembering: a Joule is a Wattsecond.
    So 3600 J = 3600 W s = 1 W h = 0.001 kW h .
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