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Topic # 22555 31-May-2008 18:40
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I think I am finally becoming a crotchety old man, I just sent a complaint to TVNZ..

I watched with interest the "power saving" item on One News, 31/5.  however I was somewhat aghast at the few seconds on heating, specifically the comment that the "fan heater was the most innefficient" and that "for a room this size an oil heater would be better".

I suggest that the reporter AND the so called expert take high school physics again.  By definition, all electric heaters are 100% efficient, that is all the electricty in eventually comes out as heat.  No exception.  For the same amount of net heat given, an oil heater and a fan heater will use exactly the same amount of electricity.  To say otherwise is stupid beyond words.

If they'd suggested a heat pump that would have been fine, heat pumps are not electric heaters and can move heat into a room more efficiently than a heater can create heat.




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  Reply # 134656 31-May-2008 19:06
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The system used in the fan heater is a fan blowing cool air onto the windings that make the heater.
This fan causes the wire to cool, cause it to use more energy keeping it hot.  Oil heaters system is softer process,
even through they may be the same watts. I would think you r right.

It is like compaing two cars by engine size and not taking into account, one of the cars is a van.



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  Reply # 134657 31-May-2008 19:10
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Perhaps you should also go back to school.  Hint: conservation of energy.




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  Reply # 134662 31-May-2008 19:28
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sleemanj: Perhaps you should also go back to school.  Hint: conservation of energy.


Well if it keeps ya warm.  What class though.  Maybe they had different usage and the fan heart was not on full.
That could be the difference.  My example,  ok, it was ungood.

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  Reply # 134666 31-May-2008 20:03
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sleemanj: For the same amount of net heat given, an oil heater and a fan heater will use exactly the same amount of electricity.

You're right about the electricity input vs heat output (ignoring the small amount of energy used to run the fan).

However, I have heard a line of argument that asserts people use oil heaters and fan heaters differently.  That is, oil heaters generally have a thermostat, so will heat a room to a certain temperature and then maintain that temperature by operating only intermittently.  Fan heaters, conversely, don't usually have a thermostat so are often just left to run continuously, thereby consuming more energy overall (and outputting more heat in the process).

I don't know how valid this assertion is, but at least it recognises that ya cannae change the laws of physics, Captain.




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  Reply # 134668 31-May-2008 20:17
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BobW:

Fan heaters, conversely, don't usually have a thermostat so are often just left to run continuously, thereby consuming more energy overall (and outputting more heat in the process).



Perhaps that's true, but people also tend to leave oil column heaters on even when there is nobody to use the heat produced, not something people generally do with fan heaters I'd expect (hard to forget a fan heater is running).

Personally I prefer an oil column heater because of the safety aspect.




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  Reply # 134669 31-May-2008 20:25
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(ignoring the small amount of energy used to run the fan).



Just to pick one tiny little nit.  you don't need to ignore that, eventually, it all is going to wind up as heat somewhere.  Of course, as you say, it's such a small amount that it's of negligible interest, but still, it's going to wind up as heat.




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  Reply # 134670 31-May-2008 20:32
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sleemanj: Perhaps that's true, but people also tend to leave oil column heaters on even when there is nobody to use the heat produced, not something people generally do with fan heaters I'd expect (hard to forget a fan heater is running).


Fair enough.

More broadly, you'll be writing many complaints to TVNZ News (and other news programs) if you expect the news to be factually accurate.  Best that you treat the news as the entertainment show that it has actually become.

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  Reply # 134671 31-May-2008 20:34
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sleemanj:

(ignoring the small amount of energy used to run the fan).



Just to pick one tiny little nit.  you don't need to ignore that, eventually, it all is going to wind up as heat somewhere.  Of course, as you say, it's such a small amount that it's of negligible interest, but still, it's going to wind up as heat.


Well yes, OK.  Though some of the energy will be converted to light, if you run the heater hot enough to make the element glow.  But now we're getting really pedantic...



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  Reply # 134673 31-May-2008 20:41
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Well yes, OK.  Though some of the energy will be converted to light, if you run the heater hot enough to make the element glow.  But now we're getting really pedantic...


Well as long as we are pedants, the light produced, also winds up as heat in something, it doesn't bounce around in the room forever ;-)




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  Reply # 134675 31-May-2008 20:47
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sleemanj: the light produced, also winds up as heat in something, it doesn't bounce around in the room forever ;-)

But maybe not heating the room, since the light escapes through the window which doesn't have the curtains closed.

Of course, closing the curtains would make much more difference to the total energy consumption, yet many people don't seem to bother.

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  Reply # 134731 1-Jun-2008 11:03
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In simple physical terms, of course all the energy is conserved.

However fan heaters and oil heaters disperse heat differently in a room. There are different thermal dynamics of air being forced over fine elements and dispersed in a certain direction rather than passively from a central point.

Thus there are differences in their efficiency in terms of their effectiveness at making it feel warm to a human being and is effected by the room size, insulation, furniture, placement relative to windows, whether the door is open, what materials they are made of, and human behaviour in terms of their usage etc etc etc.

If you are looking at energy conversion equations, of course energy is always conserved. Doesnt mean that all the energy is usable for the purpose of the conversion though. I have no idea of the actual scientific figures of which heater is best, but it is too simplistic to refer to high school physics to describe the phenomenon in the context of energy cost efficiency.

Always pays to consider the context of a news report. If they were trying to entertain physicists, they would probably give you equations of the amount of net usable energy or something. However, I would assume that it was aimed at people who want to know what is going to make them the warmest at the least cost.



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  Reply # 134747 1-Jun-2008 13:41
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mushion22:However, I would assume that it was aimed at people who want to know what is going to make them the warmest at the least cost.


I would argue that in that case the fan heater would be MORE efficient at that task than an oil column heater.  A Fan heater provides far more instant and directed heating than an oil column heater which heats a rather localised column of rising air without dispersing it well.




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  Reply # 134761 1-Jun-2008 15:29
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I had a look through my old rss feeds from TVNZ had for their article your referencing with video here.

It says the Oil heater uses less energy than a fan heater.


I have a prepayed power system, so I can monitor my power usage.  I adjusted my hotwater from 60 degres to 70 degreas,  that cause my power usage to jump up just over a $1 a day.  I'm going to put it back down as it's did make a difference that is worth $356 a year.

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  Reply # 134762 1-Jun-2008 15:30
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mushion22: ... Always pays to consider the context of a news report. If they were trying to entertain physicists, they would probably give you equations of the amount of net usable energy or something. However, I would assume that it was aimed at people who want to know what is going to make them the warmest at the least cost.


At last some common sense. Efficiency of home heating is not the same as energy conversion efficiency. Heat dispersion, quality of heating (eg. bar heater radiant type vs convection, effects of high temperature elements in bar or fan heaters on air quality, dust build up in fan heaters, moisture from unflued gas heaters), heat wastage (heating empty rooms, thermal mass heat absorption, etc), human behaviour & human perception are some factors. Generation and transmission losses are relevant to energy efficiency comparisons between fuel types. Household occupancy is also an important factor; eg. the best option for a pensioner flat mostly occupied 24 hours/day will probably be different to that for flat that is unoccupied 10 - 12 hours during the day.

Yes heat pumps are 'energy efficient', but the following table may be of interest
(http://www.mfe.govt.nz/publications/energy/warm-homes-home-heating-methods-fuels-nz-nov05/html/tables/tables-3.html#311)


Table 3.6: Type of electric heating and average cost per household, New Zealand

 

Night store

Radiant

Portable oil column

Panel

Fan

Heat pump

Don't know/ refused

Other

Households

42,995

193,478

222,141

64,493

265,137

107,488

-

64,493

Percent

5%

24%

28%

8%

33%

13%

-

8%

Cost*

$137

$100

$103

-

$84

$150

-

$152


* Cost estimates were based on responses for households using one type
of electric heating method only. No cost information was available
within this data set for households using panel heaters.


The above comparison is not really of value without knowing more about the representativeness of the houses surveyed; eg. were the heat pumps preferentially located in colder climate areas, in higher income homes, or in homes with higher occupancies (number of occupants and/or occupied hours per day), etc. And, of course, the quality of heating is not necessarily the same for all options. But it does perhaps caution against using simple "static" energy efficiency as a measure of home heating efficiency.

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