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Postby DIYvirgin1975 » Wed Mar 26, 2008 9:30 am

Can someone define KWH, what it does and how it works ?
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Postby kuzz » Wed Mar 26, 2008 2:09 pm

You should be able to work out how much it costs to run an electical appliance as long as you know its power rating, the time you use it for, and the cost of electrcity.

Energy = power × time can be used as long as power is in kW and time in hours. The formula becomes:

Units used (kWh) = power (kW) × time (h)

e.g. A 2·5 kW kettle is used for 2 hours a week. Units cost £0·08 each.
Units used = 2·5 kW × 2 h = 5 kWh
Total cost = units used × cost
= 5 kWh × £0·08
= £0·40.
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Postby thebird44 » Wed Mar 26, 2008 3:09 pm


KWH stands for Kilo Watt Hours

I'm not sure if it means something different to electricians but in the electrical supply industry it is how your electricity supply is charged for, for example a 100w light bulb will take 10 hours to use 1 unit of electricity or 1kWh of electricity, this is worked out by dividing 1kW by the rating of the appliance = 1000 watts (1kw) / 100 watts = 10hours. This way you can work out how much each electrical appliance in your house will use in units on your meter (kWh).

Your gas supply is billed in the same way but the calculation is different as i think they convert cubic meters of gas to kWh?

hope this helps
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Postby ericmark » Wed Mar 26, 2008 3:13 pm

A unit of energy like BTU, Joule, Erg, Calories etc. It means the power required to run a 1 bar electric fire for 1 hour or a kettle for 20 mins or a bulb for 10 hours. It is more manageable than Joules. 1 Watt = 1 Joule per second so 1KiloWatt = 1000 Joules per sec so 1KWH = 1000*60*60 = 3600000 Joules or 857142 calories or 857 Calories (Spelt with Caps makes it Kilocalories) you can do your own conversion to BTU if you want. Don't ask why not in MegaJoules it would make more sense.

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