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Thread: Value of the Watt / Watt Hour from BTUs - Please Verify

  1. #1 Value of the Watt / Watt Hour from BTUs - Please Verify 
    WD
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    I searched the internet for the last 2 hours learning and understanding the Watt/Watt Hour/BTU conversions using data collected.

    I am not sure what I might be missing, but Wikipedia has supported that a defined Watt ~ 3.412 BTUs.

    Some simple constants:

    1 Watt (W) = 1 Joule per second
    1 BTU ~ 1055.05585 J
    1 hour (h) = 3600 seconds (s)

    So, inherently, a simple formula can be derived to convert BTUs into what I believe should be Watts:

    W = Joules(BTU)/Seconds(Time Elapsed) OR 1055.05585/3600 ~ .293 W Rating

    Their number of 3.412 has apparently been used by applying:

    W = Seconds/Joules OR 3600/1055.05585 ~ 3.412 W

    This makes no sense to me and appears to be the inverse of a Watt.

    Once the Watt has been calculated, you simply multiply by the time of usage:

    Watts * Time (in hours)


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  3. #2  
    Forum Masters Degree Twit of wit's Avatar
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    That formulas make no sense. You are trying to convert watts to watts?

    I am not sure what I might be missing, but Wikipedia has supported that a defined Watt ~ 3.412 BTUs.
    This makes no sense. Watts can't equal BTUs, as watt is a unit of power and BTU is a unit of energy.


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  4. #3  
    WD
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    Quote Originally Posted by Twit of wit
    That formulas make no sense. You are trying to convert watts to watts?
    I am trying to get a general power rating based on energy usage and time elapsed.

    If W = J/s, then 1000 BTUs used over 5 hours would give

    (1000 BTUs * 1055 J)/(5 hours * 60 *60) ~58.6 J/s OR 58.6 W
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  5. #4  
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    It seems correct. But what is your point then? Wikipedia says
    1000 BTU/h is approximately 293.071 W
    293.071/5=58.6142W
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  6. #5  
    WD
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    Simply to calculate the Wattage rating/average of a device from usage and time elapsed. Similar to determining a lightbulbs wattage rating based on its usage
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  7. #6  
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    Before you edited your post you said that there is something incorrect in wikipedia article about BTU.
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  8. #7  
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    Quote Originally Posted by WD
    Simply to calculate the Wattage rating/average of a device from usage and time elapsed. Similar to determining a lightbulbs wattage rating based on its usage
    Why do you need such an obscure unit to calculate the wattage of a device?
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  9. #8  
    WD
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    Quote Originally Posted by Twit of wit
    Quote Originally Posted by WD
    Simply to calculate the Wattage rating/average of a device from usage and time elapsed. Similar to determining a lightbulbs wattage rating based on its usage
    Why do you need such an obscure unit to calculate the wattage of a device?
    Apparently that is how international agencies calculate energy usage
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  10. #9  
    WD
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    Quote Originally Posted by Twit of wit
    Before you edited your post you said that there is something incorrect in wikipedia article about BTU.
    Yes, the claim that 1W = 3.412 BTUs - I was incorrect and was mixing up BTU and BTU/h
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  11. #10  
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    Quote Originally Posted by Twit of wit
    Why do you need such an obscure unit to calculate the wattage of a device?
    It is not obscure in the US where BTU is often used as a measure of the heating value of fuels, or the output of an air conditioner, while watt-hours are used to measure electrical energy.
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  12. #11  
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    1 joule = 1 watt
    1 BTU = 1054 J

    1 BTU = 1054 watt if consumed over a time period of 1 second
    1 BTU = 0.2929 watt if consumed over a time period of 1 hour

    1 watt consumed in 1 second = 0.0009485 BTU

    therefore

    you can use 0.0009485 BTU * (time in seconds/3600) = BTU/time in hours

    1 watt consumed for 1 hour , 3600 seconds = 0.0009485 BTU * 3600 seconds = 3.4146 BTU/hour

    if your heater is rated at 10,000 BTU in 1 hour it will probably consume

    10,000 BTU / 3.4146 BTU/hour = 2928.600 watts per hour or 2.928 kW/h
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