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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

        Comment


        • #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 ????

              Originally posted by Unregistered
              that ******* is wrong! i failed my test because of him!!!
              no, Robert's answer is not wrong. kWh is KiloWatts Per 1 Hour. if a water heater had a 4.5 kW heating element, that ran for 1 hour (60 minutes, or 3600 seconds) --which is exactly what the question asked-- it would consume 4.5 kWh of power.

              Comment


              • #8
                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

                Comment


                • #9
                  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


                  • #10
                    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, 08:05 PM.

                    Comment


                    • #11
                      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

                      Comment


                      • #12
                        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


                        • #13
                          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


                          • #14
                            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


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

                              Originally posted by Unregistered
                              Wow...

                              Lets set this matter straight:

                              READ: Kilowatts can not be CONVERTED into Kilowatt-hours, PERIOD!
                              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)
                              Originally posted by Unregistered
                              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.
                              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
                              Originally posted by Unregistered
                              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.
                              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
                              Last edited by gubment_cheez; 11-16-2008, 12:19 PM. Reason: wikipedia is my friend, and SHOULD BE YOURS TOO!

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