Efficiency of Electric Heating

[stem]

My mother is looking to buy a convector heater with thermostatic control for very occasional winter use of a small conservatory. So asked me for advice regarding which model would be the cheapest to run. I told her there would be no difference as electric heaters were all 100% efficient, in that a 3 Kw heater from any manufacturer would consume 3 Kw of electricity and produce 3 Kw of heat. She understood, and I left it at that.

Today she called me and said that I am wrong, based on a statement on Dimplex website in reference to their Cadiz ECO model. Which states that this model uses micathermic heating technology to give a 30% energy saving (based on a lab test heating a room 10 degrees C to 22 degrees C)

The web page can be found here

Based on this, mum believes Dimplex have developed a heater that emits 3000 kW of heat and yet will only consume 2100 kW of electricity, or more importantly to her, that she will pay 30% less using a 3 kW Cadiz ECO, to heat her conservatory than if she used a heater of the same rating, but made by another manufacturer. This sounds impossible to me (heat pumps excepted of course) so can anyone tell me what's going on here? and what are they actually saying?

 

[bernardgreen]

They compare it to an oil filled heater.

In a small room the amount of energy required to heat the oil will be significant compared to the amount of heat required to heat the room.

If it has no oil or other thermal mass to heat up then all the heat produced goes directly into the room therefore with this heater a room will heat up sooner than it would with an oil filled heater. The smaller the room the more pronounced this apparent saving will be.

Oil filled heaters can waste energy by still having hot oil after the room no longer needs heating.

 

[JohnW2]

I told her there would be no difference as electric heaters were all 100% efficient, in that a 3 Kw heater from any manufacturer would consume 3 Kw of electricity and produce 3 Kw of heat. She understood, and I left it at that.

Quite so.

Today she called me and said that I am wrong, based on a statement on Dimplex website in reference to their Cadiz ECO model. Which states that this model uses micathermic heating technology to give a 30% energy saving (based on a lab test heating a room 10 degrees C to 22 degrees C)

As above, one can't defy the laws of physics. They might be playing a game by talking about the initial phase of heating (all of) a room from cold. A fixed input/output fan heater would probably heat (all of) a room to a given temperature more quickly (hence less electricity used) than would a fixed input/output non-fan heater (particularly one which has initially to heat up a pile of oil) - but that's really all about distribution of heat.

In terms of maintaining a given temperature in a given room, long-term, it has surely got to be nonsense?

Kind Regards, John

 

[JohnD]

I can't see the evidence to support their advertising claim and I am suspicious of the contrived test conditions they used. Usually crooks who make dodgy claims are selling very expensive heaters. If she wanted a non-oil-filled convector, she could get one for about £20 in Aldi or Tesco. However people who fall for this sort of advertising get a warm glow from the knowledge that they have spent lots of money.

It would be interesting to know if they have made this claim in newspaper adverts where it would be subject to ASA rules and they could be compelled to prove it.

Unless she only wanted to heat the room for a few minutes, the ramp-up time will not be significant. Personally I prefer oil-filled because they are safer and give a more regular heat due to their thermal mass.

 

[ban-all-sheds]

It is impossible.

What they are saying is that starting from cold it will bring a room up to temperature quicker than an oil-filled radiator (because it's not having to heat up the oil), and so uses less electricity to do that.

But it will still use electricity at a rate of 2 or 3kW while it's on. Over the long term it cannot use any less than any other electric heater to put a certain amount of heat into a room.

http://www.ehow.co.uk/facts_7910889_differences-heaters-oilfilled-radiating-heaters.html

With either an oil-filled radiator or one using "unique micathermic heating technology" ( ), there will be a time lag between turning it on and the room getting warm, it'll be shorter with the latter, that's all. And the latter will put out heat for less time after it's turned off.

But if her use is to be occasional, (and presumably at short notice, and for an indeterminate time?) no heater which has a lag is the best sort - I would suggest a fan heater which will be the fastest way to get the air warm and which will not be storing heat to give out after she's finished using the conservatory.

Or an air-source heat pump, which will use less electricity but will cost more and have quite a long break-even period

 

[JohnD]

I suggest we all email them and ask for the evidence to support their claim.

 

[Jackrae]

Occasional use conservatory - fan heater every time for me

 

[stem]

Oil filled heaters can waste energy by still having hot oil after the room no longer needs heating.

So, if I understand correctly, in the test they heat a room from 10 degrees to 20, then when the temperature is reached the heaters are turned off and the energy they have used is measured. Because of the 'physics' of the oil filled heater it takes longer to warm up and so consumes more energy to reach the set temp (lets say 30% ) What they completely ignore is that the oil filled heater will then emit the extra heat after it is switched off, whilst the convector will cool immediately having already lost most of its heat.

So after initial warm up, the energy consumption would then average out the same.

If so, I think that the website is a bit misleading, I wonder who many others would have read that at face value and assumed a 30% saving.

 

[ericmark]

How I read it is if a oil filled radiator is used it has to be switched on 65% earlier than with the new micathermic heating so if for example the old one was switched on 1 hour before you want to use the room the new one is switched on 21 minutes before you enter the room.

There is likely also saving in more accurate control if we want a room at 20°C then with old heaters we switch off at 22°C and back on at 20°C if instead we use solid state switching instead of switching every 15 minutes we can switch every few seconds so if you want 20°C the heat heats to 20°C.

There are three forms of heating forgetting a heat pump then down to two. Radiation and Convection can't really use conduction unless a heated chair.

Radiation needs the unit to be red hot and also is near impossible to control as must thermostats are measuring air temperature and radiated heat does not heat the air. Also clearly no good for a conservatory as it passes through glass that's how we feel the suns heat.

But to combine radiation with convection does work especially once curtains are closed. So to combine heat and light and have tungsten lamps which give out radiated heat and radiators (bad name really) which gives out convected heat the air temperature can be reduced and still feel comfortable so during the winter tungsten bulbs are energy saving as they reduce the air temperature required at night and the curtains are closed so heat does not escape.

One could combine radiated heat and convected heat in other ways for example the single bar electric fire with reflector.

The problem is the government measuring scheme can warp information so we have cars rated at 200+ miles per gallon when really only 40 mile per gallon because the scheme does not include battery power.

This is repeated again and again fridge/freezer is measured different to a stand alone fridge and stand alone freezer so USA stile fridge/freezer is A++ rated and two matching fridge and freezer units are rated A+ even though they use the same power.

Tungsten bulbs are not energy saving even though in doors in winter with an electric heated house they save energy.

To get to nitty gritty as I found with refrigeration you have to find out the testing standards with refrigeration the standard annual energy consumption (SAEc) what the problem clearly done years ago and very much dated which has caused the demise of the 40/60 split fridge/freezer today fridge is always bigger than the freezer.

I am sure if you delve into the conditions to test a heater you will find something similar like power required to heat a room to 20°C for one hour. Fact most want the room at 20°C for more than an hour is besides the point.

So if an oil filled radiator retains 30% of the energy used after it is switched off then a heater which retains no energy after switch off will be 30% more efficient.

However to get that 30% saving you must only use the heater for the time stipulated in the government test data. As you exceed that time then so the saving is reduced.

So use a fan heater and on switch off it's cold within a minutes or two so that uses less power than an oil filled radiator which in turn using less power than a storage radiator.

Other than heat pump likely cheapest is an inferred lamp and fan heater combination clearly aimed correctly as the lamp will reduce the back ground heat required to be in the comfort zone and the fan heater will control the back ground heat level quicker than any other heater with of course an electronic relay controlling the elements heat output so it does not switch off but regulates the power used.

One I don't want an inferred lamp shining at me all day and two I down want a fan heater weering away all day and three as far as I know there is no fan heater with a SCR thermostatic control made. (Bet some one finds one!)

So in real terms what you said is correct.

 

[JohnW2]

So, if I understand correctly, in the test they heat a room from 10 degrees to 20, then when the temperature is reached the heaters are turned off and the energy they have used is measured. Because of the 'physics' of the oil filled heater it takes longer to warm up and so consumes more energy to reach the set temp (lets say 30% ) What they completely ignore is that the oil filled heater will then emit the extra heat after it is switched off, whilst the convector will cool immediately having already lost most of its heat. ... So after initial warm up, the energy consumption would then average out the same.

I reckon that's about it - plus the fact that, with the the oil-filled heater, it may take longer for heat to spread out evenly in the room (if, say, their gizmo is better at 'convecting) - so perhaps longer before the temperature in some corner reaches the target figure.

If so, I think that the website is a bit misleading, I wonder who many others would have read that at face value and assumed a 30% saving.

Very potentially misleading, I would say - but, as has been discussed, they have been pretty careful in the wording of what they say, which might actually be correct in terms of the precise test conditions they describe.

Kind Regards, John

 

[ericmark]

Oil filled heaters can waste energy by still having hot oil after the room no longer needs heating.

So, if I understand correctly, in the test they heat a room from 10 degrees to 20, then when the temperature is reached the heaters are turned off and the energy they have used is measured. Because of the 'physics' of the oil filled heater it takes longer to warm up and so consumes more energy to reach the set temp (lets say 30% ) What they completely ignore is that the oil filled heater will then emit the extra heat after it is switched off, whilst the convector will cool immediately having already lost most of its heat.

So after initial warm up, the energy consumption would then average out the same.

If so, I think that the website is a bit misleading, I wonder who many others would have read that at face value and assumed a 30% saving.

You two have condensed what I said very well. OK you did it even before I posted so has to be full marks. What I would like to know with the test where would a storage radiator fit?

What to me is wrong is to compare an oil filled radiator with a simple convection radiator.

I can see the point using SCR control the heat output is similar to an oil filled in there is a reasonably consent output but it's still like comparing a mini with a landrover both carry 4 people and mini does more to the gallon just forget about other features.

 

[bernardgreen]

Eric's comment about tungsten lamps saving energy is very valid. The warm glow from them has a psychological effect in that many people feel a room is warmer when there is "warm white" light compared to when the light is brilliant white. My lighting set up enables two 230 volt lamps to be connected in series so each lamp gets 115 volts and glows with a very warm light which does make the room "feel" warmer than it actually is. ( comments from visitors )

 

[stem]

Thanks everyone for your fast and comprehensive replies. I think we'll go for a combined 3kW convector with built in fan. That way we can have the fast warm up with the fan and then just use the convector to maintain the
temperature. Something like this.

Untitled

• stem
• 24 Nov 2014
• 1

I see several mentions of heat pumps, which would be a nice idea, but as most have realised, the initial outlay is a bit high considering that the conservatory will probably only be heated for 40 hours tops all winter.

 

[stem]

I suggest we all email them and ask for the evidence to support their claim.

Better still, I'll write to Watchdog and see if Anne Robinson can do it

 

[ericmark]

Eric's comment about tungsten lamps saving energy is very valid. The warm glow from them has a psychological effect in that many people feel a room is warmer when there is "warm white" light compared to when the light is brilliant white. My lighting set up enables two 230 volt lamps to be connected in series so each lamp gets 115 volts and glows with a very warm light which does make the room "feel" warmer than it actually is. ( comments from visitors )

I had a lamp and a soldering iron in series in the same way. And yes always felt warmer with two in series than when the lamp was shorted out to get iron to full heat.

I looked at the idea of inferred lamps to heat areas as and when used but electric costs so much more than gas it may use less energy but still costs more to run.