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kWh / KW ????

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  • kWh / KW ????

    I see on my bill I used 703KWH last month. My water heater has a 4500 watt (4.5KW) element in it. If I ran the unit continually for 1 hour how would I calculate the KWH?
    Thanks,
    Mark

  • #2
    Re: kWh / KW ????

    As its name implies, kilowatt hours is indeed kilowatts * hours.

    4.5 kilowatts * 1 hour = 4.5 kWh

    Comment


    • #3
      Re: kWh / KW ????

      thx for helping with my energy econ homework

      Comment


      • #4
        Re: kWh / KW ????

        Thanks for helping me with my homework too =D

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        • #5
          Re: kWh / KW ????

          thanks for doing my homework

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          • #6
            Re: kWh / KW ????

            that ******* is wrong! i failed my test because of him!!!

            Comment


            • #7
              Re: kWh / KW ????

              kilowatt-hour (kWh) is a unit of Power. 1 kilowatt-hour means that it will use (or transfer) one kilowatt every hour. One kilowatt is the power of one thousand joules (J) per second (s). the h in kWh basically signifies just the alternative time unit used. It is used because it often provides results that can be explained in whole numbers easily with out common household appliances.
              If you really want to know what the conversion for kWh to kW...
              1 kWh = 0.000277777...kW
              1 kW = 3600 kWh

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              • #8
                Re: kWh / KW ????

                The conversion:
                1 kWh = 0.00027777... kW
                1 kW = 3600 kWh
                1 kW = 1000 J / s

                So, the answer would be 4.5 kW = 16200 kWh, or 16.2 mWh (megawatt-hours)

                Comment


                • #9
                  Re: kWh / KW ????

                  1 kW = 1 kW consistent for 1 hour, or 1 kWh
                  1 kW = 1000 J / s = 1 kJ / s
                  1 kWh = 1000 J / h = 3.6 kJ / h
                  kW (kilowatts), kWh (kilowatt-hours), J (Joules), s (seconds), h (hours), kJ (kilojoules), mJ (megajoules)
                  But if you ant to find how much power was consumed in an hour, then you multiply 1 kWh times 3600. You can look above to find conversions to Joules per second, and, including the units, you find that the two time units cancel out each other:
                  kWh / kW = (1000 J / h) / (1000 J / s)
                  = (3600000 J / s) / (1000 J / s)
                  = (3600000 J / s) * (s / 1000 J)
                  = 3600

                  Just some prefixes for units if you ever want to know.
                  (f) fempto = 0.000000000000001
                  (p) pico = 0.000000000001
                  (n) nano = 0.000000001
                  (micro symbol) micro = 0.000001
                  (m) milli = 0.001
                  (k) kilo = 1,000
                  (M) mega = 1,000,000
                  (G) giga = 1,000,000,000
                  (G) tera = 1,000,000,000,000
                  (P) peta = 1,000,000,000,000,000

                  For your information

                  If anything is wrong, tell me now and prove it. I always want to be right.

                  Oh, and Mark, the heater used 4.5 kWh, and it will consume 108 kWh daily if you leave it on 24/7.
                  Last edited by Pizza_Pi; 12-04-2007, 09:05 PM.

                  Comment


                  • #10
                    Re: kWh / KW ????

                    passing by... Actually KWH is the unit of Energy or Work. Instead, KW is the unit of Power. 1 KWH= 1KW * 1Hour. (Work=Power * Duration)

                    Joule is also the unit of work or energy. 1 Joule = 1 Watt * 1 s. 1KWH=1000 * 3600 =3.6 MJ

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                    • #11
                      Re: kWh / KW ????

                      Wow...

                      Lets set this matter straight:

                      READ: Kilowatts can not be CONVERTED into Kilowatt-hours, PERIOD!

                      They are two different units of measurement!

                      A Kilowatt is a unit of POWER or the RATE OF ENERGY CONSUMPTION (or production).

                      A Kilowatt hour is a unit of ENERGY, much like the Joule, Calorie, etc.

                      YOU CANNOT CONVERT BETWEEN THE TWO

                      Simply put:
                      A Kilowatt hour IS the amount of energy you are using
                      A Kilowatt is how fast you are using it.

                      Comment


                      • #12
                        Re: kWh / KW ????

                        I'm interested to read the comments above.

                        As an ex plumber and now a Public health Engineer (a plumber with a shirt and tie on) we often use gas load calculations in our work and as far as I was concerned the calculation went something like this:-

                        1 kilowatt-hour = 3600 kilo-joules (KJ) - check this on any other web sites.

                        1 KJ/s (kilo-joule per second = 1 kw of energy used every second (remember your basic formula - 1KJ/s = 1Kw)

                        so 1 kWh = 3600 x 1KJ/s = 3600 x 1 kw

                        If you have a 1 kw heater it uses 1 kilowatt of energy for every second it is on otherwise it couldn't be rated. How could you rate a fire accurately as a 1 kw heater if this related to 1 hours use. If I had it turned on for 1 hour and you had it turned on for 20 minutes - in my eyes it would be a 1 kw heater and in your eyes it would be a 1/3 kw heater.

                        Comment


                        • #13
                          Re: kWh / KW ????

                          Originally posted by Pizza_Pi
                          1 kW = 1 kW consistent for 1 hour, or 1 kWh
                          1 kW = 1000 J / s = 1 kJ / s
                          1 kWh = 1000 J / h = 3.6 kJ / h
                          kW (kilowatts), kWh (kilowatt-hours), J (Joules), s (seconds), h (hours), kJ (kilojoules), mJ (megajoules)
                          But if you ant to find how much power was consumed in an hour, then you multiply 1 kWh times 3600. You can look above to find conversions to Joules per second, and, including the units, you find that the two time units cancel out each other:
                          kWh / kW = (1000 J / h) / (1000 J / s)
                          = (3600000 J / s) / (1000 J / s)
                          = (3600000 J / s) * (s / 1000 J)
                          = 3600
                          First of all, kW is a unit of power, kWh is a unit of energy, and a Joule (J) is a unit of energy. You cannot say that X kW = Y kWh = Z J/s, that's comparing apples to oranges.
                          1 kW = 1000 J/s (power)
                          1 kWh = 1000 Jh/s (energy)
                          1 h = 3600 s (time)
                          1 kWh = 1000 Jh/s = (3600*1000) Js/s = 3600000 J (energy)
                          To correct your final statement in the quote:
                          1kWh/1kW = (3600000 J)/(1000 J/s) = (3600000 J)*(s/1000 J) = 3600s = 1h
                          As you can see the Joules cancel out and you are left with a unit of time.
                          If you run your water heater which uses a steady 4.5kW of power for 1 hour you will have consumed a total of 4.5kWh of energy, if you used it for 2 hours straight it would consume 9kWh of energy.

                          Comment


                          • #14
                            Re: kWh / KW ????

                            Originally posted by gubment_cheez
                            incorrect. a kilowatt-hour is simply a second dimension on kilowatt (example, kilowatt is a 1 dimensional line, a kilowatt-hour would be a 2 dimensional graph) this is not correct. if I recall correctly,

                            a joule is the energy used by a force of one newton moving one meter.

                            a calorie is the amount of energy required to heat 1 gram of water 1 degree Celsius.

                            a kilowatt hour is the product of power in kilowatts, multiplied by hours
                            to clarify something,

                            a kilowatt is 1 000 watts

                            and,
                            a watt is the the rate at which work is done when an object is moving 1 meter a second against the force of 1 newton
                            A joule is also the energy of an electromotive force of 1 V moving a charge of 1 C. If it occurs in in 1 s, then it is 1 V moving 1 A, and the resulting power is 1 W. 1 W = 1 J/s, or 1 J = 1 W·s.

                            Clearly a watt-hour is 3600 W·s = 3600 J, and a kilowatt hour is 1000 W x 3600 s = 3.6 MJ.

                            The use of the accursed kilowatt-hour obscures the fact that electrical energy may be expressed in exactly the same units and form as mechanical or thermal energy. It should be deprecated, much like the calorie. Of course, the calorie is also deprecated because it comes in at least five flavors of slightly different size because the heat capacity of water is not constant enough to be an acceptable standard. (then, there is the whole big calorie, little calorie thing differing by 3 orders of magnitude)

                            Comment


                            • #15
                              Re: kWh / KW ????

                              Originally posted by Pizza_Pi (Visitor)
                              kilowatt-hour (kWh) is a unit of Power.
                              Not so. The kilowatt is a unit of power. A kilowatt·hour is a unit of energy. If everything is constant load, it is the product of power in kilowatts and time in hours.

                              For flucuating loads, it is the integral of P(t)*dt

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