power usage and cost advice for 15kw

[mattysupra]

Hi,

Need temporary heating (long story)

Looking at some 415v 15kw heaters.

Question 1-

the 15 kw, does that mean it uses 15kw of electric PER Hour ?

Question 2-

Anyone know what the average cost of 1kw of electric is? Or better still maybe tell me how much per hour im looking at to run a 415v 15kw heater please.

Thanks

 

[AdrianUK]

Q1 - Yes, the heater will use 15kwh every hour it is running.

Q2 - that depends upon your tariff, assuming this is commercial then you could do a very rough calculation at 10p per kwh ie. a 15kw heater is gonna cost you, ballpark, £1.50 per hour.

Adrian

 

[ban-all-sheds]

the 15 kw, does that mean it uses 15kw of electric PER Hour ?

No - it means it uses 15kW. There is no time dimension.

Anyone know what the average cost of 1kw of electric is?

Depends how long you consume 1kW for.

Or better still maybe tell me how much per hour im looking at to run a 415v 15kw heater please.

£1.50?

 

[mattysupra]

So one of you says

YES- 15kw means it will use 15kw of electric over a hour. ( so after 1 hour of running my electric meter should of gained 15kw ???)

Then the other says NO ?

Which is correct?


Anyone else that can help me?

 

[AdrianUK]

I said it would use 15kwh (kilowatt hours) per hour. That is the amount of energy that will have been consumed by the heater each & every hour that it runs.

 

[ricicle]

If the heater is on constantly (on demand) then it will consume 15kw per hour which means you will have used 15kwh after the first hour, 30kwh after the second and so on.
If there is a thermostat controlling the heating elements and the elements were only on demand for 30 mins out of every hour then that would mean 7.5kwh after the first hour, 15kwh after the second hour etc.

 

[mattysupra]

I said it would use 15kwh (kilowatt hours) per hour. That is the amount of energy that will have been consumed by the heater each & every hour that it runs.

Sorry to be stupid here, i think i understood what you said the first time around but Ban-all-sheds has confused me!

So a heater with a 15kw rating will make me electric meter gain 15kwh every 1 hour that passes?

Sorry to have to check again but like i say i have been confused by Bans comment.

 

[mattysupra]

If the heater is on constantly (on demand) then it will consume 15kw per hour which means you will have used 15kwh after the first hour, 30kwh after the second and so on.
If there is a thermostat controlling the heating elements and the elements were only on demand for 30 mins out of every hour then that would mean 7.5kwh after the first hour, 15kwh after the second hour etc.

Ok, thanks, so the same as what Adrianuk was implying. (which i understood and thought was correct when i asked the question.)

It will defo be on all the time as i have been told we need a boiler with 70kw output to heat the place up to 21c so this heater will be just taking the chill off the place.

I say the above as i presume if i need a boiler with a 70kw output then if i was to use electric heaters i would need the same rating as a boiler?

 

[Click4]

its hard to quantify, as on a higher setting it will use more quicker than on a lower setting.

if you have it on a low setting its not going to use 15Kw per every hour of use.

whereas the highest setting might... also depends on if thats 1 hour continuous or 1 hour spread out

 

[ban-all-sheds]

YES- 15kw means it will use 15kw of electric over a hour. ( so after 1 hour of running my electric meter should of gained 15kw ???)

Then the other says NO ?

Which is correct?

The second one, but that's because you misquoted the first one.

Watts = Volts x Amps. There is no time component - it is the rate at which energy is consumed or generated (although strictly speaking you can't do either, just change it from one form to another).

And just like in your job, you'll want to be paid based on how long you do it for. It's the same with the people who sell you your electricity - each of those heaters will be consuming 15kW, but what you'll pay will depend on how long you run them. 1 "unit" of electricity is 1kWh, i.e. it's what you use if you consume at the rate of 1kW for 1 hour.

Or in the case of your heater, at the rate of 15kW for 4 minutes.

http://en.wikipedia.org/wiki/Watt#Confusion_of_watts.2C_watt-hours.2C_and_watts_per_hour

It might amuse you to know that every minute that heater consumes about the amount of energy that's in a stick of dynamite. Do not try to take the chill off your building by setting off a stick of dynamite every minute though.

 

[mfarrow]

Watts = Volts x Amps. There is no time component - it is the rate at which energy is consumed or generated

I understand what you're trying to argue, however by definition there is a time component to the unit of Watts (Joules per Second) or else it would not be a rate of energy consumption.

By applying a time component to the numerator (the "h", or 3600 seconds) to get Wh or kWh, we are transposing this back into the units of energy consumed.

You should have argued that as the time component exists, kW alone as a unit of measurement cannot define the number of units of energy consumed by an appliance.

 

[JohnW2]

It might amuse you to know that every minute that heater consumes about the amount of energy that's in a stick of dynamite.

That may well be true - but the difference, of course, is that the dynamite releases all that energy in a fraction of a second, but with the heater, the same amount of energy is released gradually/leisurely over a whole minute.

Kind Regards, John

 

[ban-all-sheds]

If the heater is on constantly (on demand) then it will consume 15kw per hour

No - that's wrong.

It's the sort of statement which adds to the confusion.

The heater will not consume 15kW per hour, it will consume 15kWh per hour.


It's this confusion which leads retailers to only quote the kWh rating of ovens, which is no use whatsoever for being able to work out how much current the draw and therefore what sort of circuit they need.

It's important to get it right.

 

[JohnW2]

Watts = Volts x Amps. There is no time component - it is the rate at which energy is consumed or generated

You should have argued that as the time component exists, kW alone as a unit of measurement cannot define the number of units of energy consumed by an appliance.

... or, perhaps simpler, just omit the "There is no time component -" bit from his statement. The rest is then correct, explaining that Watts (power), a measure of the rate of energy cionsumption, which does not tell one the total amount of energy used until one multiplies it by time.

... just like saying that a car travels at a constant 30 mph does not tell you how far it's gone unless one multiplies it by the duration of the journey.

Kind Regards, John

 

[ricicle]

If the heater is on constantly (on demand) then it will consume 15kw per hour

No - that's wrong.

It's the sort of statement which adds to the confusion.

The heater will not consume 15kW per hour, it will consume 15kWh per hour.


It's this confusion which leads retailers to only quote the kWh rating of ovens, which is no use whatsoever for being able to work out how much current the draw and therefore what sort of circuit they need.

It's important to get it right.

Which is why I wrote:-

If the heater is on constantly (on demand) then it will consume 15kw per hour which means you will have used 15kwh after the first hour

Maybe I should have wrote it will consume 15kw for an hour