Electric heater comparison

Cardew

Talldave said:

A fan's primary outputs are motion and noise, heat output is minimal.  Taking the above examples to the extreme, a fan heater with a 5w element and a 995w fan would produce a massive gust of air at a temperature indistinguishable from room temperature. 

The end result would be the the room would warm by the same amount as any other 1kW device being used in the room.

Mickey666

Cardew said:

Mickey666 said:

Interesting examples.
I suppose it depends on whether the energy used by the various fans is ALL turned into heat.  Some of it certainly will be (and the motor will get hot as a result) but what about all the air being moved about?  It takes energy to do the 'work' of moving air and if ALL that energy turns into heat then where does the energy come from to do the work of moving the air?
Similarly with the 100W lamp.  A certain amount of that 100W will be converted into light (the amount being dependent on the lamp efficiency), so surely that amount cannot be converted into heat?
Also, more intuitively, will a 1kW fan really heat up a room as effectively as a 1kW heater?

The energy to turn the fan is electricity, but the heat produced by the fan is the friction of the air moving( and the heat of the motor)

There are thousands of websites on this subject, mainly concerned with calculating the heat produced by friction of an object passing through a gas e.g. a plane flying through air or a space capsule on re-entry

I wondered about the friction of moving air causing heat, which makes sense in theory but which seems counter-intuitive.
Just to clarify, you're saying a 1kW fan will heat a room exactly the same amount as a 1kW heater?

matelodave

Mickey666 said:

Cardew said:

Mickey666 said:

Interesting examples.
I suppose it depends on whether the energy used by the various fans is ALL turned into heat.  Some of it certainly will be (and the motor will get hot as a result) but what about all the air being moved about?  It takes energy to do the 'work' of moving air and if ALL that energy turns into heat then where does the energy come from to do the work of moving the air?
Similarly with the 100W lamp.  A certain amount of that 100W will be converted into light (the amount being dependent on the lamp efficiency), so surely that amount cannot be converted into heat?
Also, more intuitively, will a 1kW fan really heat up a room as effectively as a 1kW heater?

The energy to turn the fan is electricity, but the heat produced by the fan is the friction of the air moving( and the heat of the motor)

There are thousands of websites on this subject, mainly concerned with calculating the heat produced by friction of an object passing through a gas e.g. a plane flying through air or a space capsule on re-entry

I wondered about the friction of moving air causing heat, which makes sense in theory but which seems counter-intuitive.
Just to clarify, you're saying a 1kW fan will heat a room exactly the same amount as a 1kW heater?

Thats exactly what Cardew is saying.
However the heat may be perceived as feeling different depending on how the heat is produced but if they were both installed in a similarly sized, extremely well insulated space then the resultant temperature rise within the space should be the same.

Cardew

Mickey666 said:

I wondered about the friction of moving air causing heat, which makes sense in theory but which seems counter-intuitive.
Just to clarify, you're saying a 1kW fan will heat a room exactly the same amount as a 1kW heater?

Firstly it 'ain't' my theory its that bloke called Einstein who stated you can't destroy energy.

It is not only counter-intuitive but in practice wouldn't 'heat the room the same amount'  unless the room was completely airtight. The gale blowing around the room would inevitably cause some of the warmed air to escape.

To put things in perspective some of the 24 inch fans shown here https://www.google.com/search?client=firefox-b-d&q=large+fans

use 160 watts at full speed, so even six of them in a room will consume less than 1kW - so I am not suggesting using a fan to warm a room!! but the principle is correct.

Just measured the consumption of the fan on a nominal 3kW fan heater and it is 2 watts.

Talldave

Mickey666 said:

Cardew said:

Mickey666 said:

Interesting examples.
I suppose it depends on whether the energy used by the various fans is ALL turned into heat.  Some of it certainly will be (and the motor will get hot as a result) but what about all the air being moved about?  It takes energy to do the 'work' of moving air and if ALL that energy turns into heat then where does the energy come from to do the work of moving the air?
Similarly with the 100W lamp.  A certain amount of that 100W will be converted into light (the amount being dependent on the lamp efficiency), so surely that amount cannot be converted into heat?
Also, more intuitively, will a 1kW fan really heat up a room as effectively as a 1kW heater?

The energy to turn the fan is electricity, but the heat produced by the fan is the friction of the air moving( and the heat of the motor)

There are thousands of websites on this subject, mainly concerned with calculating the heat produced by friction of an object passing through a gas e.g. a plane flying through air or a space capsule on re-entry

I wondered about the friction of moving air causing heat, which makes sense in theory but which seems counter-intuitive.
Just to clarify, you're saying a 1kW fan will heat a room exactly the same amount as a 1kW heater?

It's ludicrous. Electricity isn't only ever converted into heat. If that were the case, Nissan Leaf owners would be walking everywhere while their driveway got hot and I'd be able to heat the house by watching a movie at high volume.

Cardew

Talldave said:

It's ludicrous. Electricity isn't only ever converted into heat. If that were the case, Nissan Leaf owners would be walking everywhere while their driveway got hot and I'd be able to heat the house by watching a movie at high volume.

That isn't what Einstein stated. He stated:

“Energy cannot be created or destroyed; it can only be changed from one form to another.”

I don't understand your analogy about a Nissan Leaf - the electricity is stored in a battery.

Watching a movie at high volume would work! as long as your room was airtight and sound proof(and thus would cause you to die if it stayed that way   Where would the energy go? i.e. how would the energy be destroyed?

There are millions of websites on this subject from the very simple(my level) to people trying to prove E=mc2 is flawed - they have all failed I believe; albeit Donald Trump will no doubt call it 'Fake News'!

Time for me to opt out in this thread - as it is about types of electrical heater.!

danrv

matelodave said:

If thats your plan then just dont look at costs - you need to know how much you use in kwh, not £££'s.

Read your meters at least twice a day for a few weeks, before you go to bed when most stuff is off and in the morning before you start turning stiff on, so you can get a view of you day/night consumption especially if you've still got your hot water on off-peak. Its the only way you can determine whether a single rate tariff will work for you.

 However  don't be surprised if your electricity bill sky rockets whilst you are using "on-demand" heating on an off peak tariff because peak rates ae generally around twice the cost of the off-peak one although you do have the flexibilty of only heating one room at a time.

Might be too soon for calculations using the convectors but over nine days from 24/12/20 to 1/1/21 I’ve used 173kwhs.
95kwh off peak
78kwh peak
Includes hot water on off peak.
At 12.969p a unit, off peak use amounts to £12.32.
At 20.408p a unit, peak use amounts to £15.91.
Total £28.23 over nine days.

Gerry1

Now do the sums again using the best E7 rates you can find, guesstimating the day/night split for the different off peak period(s).

danrv

Gerry1 said:

Now do the sums again using the best E7 rates you can find, guesstimating the day/night split for the different off peak period(s).

Ok thanks.
My current off peak time is mostly in the day (5.10am - 3.10pm) which is a bonus.
This is offset though by the expensive unit rates.  
Not too sure how to go about guesstimating off peak/peak usage on E7. I have the unit rates from Bulb and OVO.
With the usual E7 times, it’s going to be mostly hot water heating for an hour or so during off peak.

Gerry1

danrv said:

Gerry1 said:

Now do the sums again using the best E7 rates you can find, guesstimating the day/night split for the different off peak period(s).

Not too sure how to go about guesstimating off peak/peak usage on E7.

Just read the existing meters at the start and finish of the E7 times in your area.  Your region number is in the bottom left of the S-Number panel on your bill.