Looking for a ceiling fan

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Looking for a ceiling fan

Postby stivzor » Tue Jul 24, 2012 9:12 am

Hi solsters,
I'm looking for a 12V low-powered ceiling fan that would help to circulate warm air during Winter.

I came across this one which sounds ideal:
https://solarconduit.com/shop/heat-cool ... emote.html

It has a low speed which only uses 0.5 amps. Does anyone know if there are any local distributors for these or something similar? The only ones I have been able to find are much uglier and more expensive.

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Re: Looking for a ceiling fan

Postby zzsstt » Tue Jul 24, 2012 12:31 pm

Remember that the fan uses power to move air. If a 240V ceiling fan has a 70W motor, and still uses 15W on low speed, how much air will be moved by a similarly designed fan that uses 15W on high speed? Having said that, most of our fans are only ever run on low speed so it might in fact be enough, but it is still worth considering.

Another point is that this fan appears to mount directly to the ceiling, with an 8" pendant mount as an option. The air that is moved by the fan has to go to, and come from, somewhere. Normal practice is that the fan is 12" or more from the ceiling to allow air circulation. In the winter a ceiling fan is normally operated in reverse, pushing air upwards to distribute the warm air. A fan directly on the ceiling won't work very well in either direction!

Lastly, whilst I don't know of an importer of that fan, experience would suggest that if there was one they would be charging somewhere around twice the US price, so I would anticipate AU$250.

Out of interest, acting as your personal Google proxy, a quick search for "12V ceiling fan" comes up (top of the list) with http://www.offgridaustralia.com/products/12v-dc-remote-control-ceiling-fan listed at just $275
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Re: Looking for a ceiling fan

Postby Gordon-Loomberah » Tue Jul 24, 2012 12:44 pm

Yes, it does seem a bit too close to the ceiling for effective operation, except at low speed where not much air is boing moved.

zzsstt wrote: In the winter a ceiling fan is normally operated in reverse, pushing air upwards to distribute the warm air.


That "normal practice" is completely unnecessary IMO, it really makes no difference if the warm air is blown down in the middle of the room and cold air moves up the walls, or the warm air moves down the walls- the aim is to mix the air and prevent stratification, where a warm layer develops at the top of the room, and the air near the floor stays cold. For quite a few years I used a ceiling fan to distribute heat (from the fan-assisted fire box I built out of 1/4" steel plate) in a room, and right through the whole house when used on high speed.
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Re: Looking for a ceiling fan

Postby zzsstt » Tue Jul 24, 2012 1:27 pm

Gordon-Loomberah wrote:That "normal practice" is completely unnecessary IMO, it really makes no difference if the warm air is blown down in the middle of the room and cold air moves up the walls, or the warm air moves down the walls- the aim is to mix the air and prevent stratification


You may be right, but it may depend on the situation and speed of the fan. We have fans in almost every room. Most are not used in winter, and when they are used they are never "reversed", with the exception of the fan in the kitchen/family room. That fan is located just in front of the wood burner, and above a table. For some reason in winter it seems to make the room far more comfortable when reversed than when pushing down, and I also think that it pushes more heat out to the hallways. My suspicion is that by pushing air up in the middle of the room, it causes the warm air trapped at ceiling level, but not directly stirred by the fan, to move towards the walls and therefore out through the doors to the halls. The doorways (archways) form an inverted dam, trapping the warm air in the room, and perhaps the fan pushing the warm air outwards forces it "under" (over?) that dam? When pushing air downwards the warm air is mixed with the cooler floor level air, but perhaps the circulation is more local because it is working against the "warm air rises" principle rather than with it?

It may also depend on the speed of the fan - a low speed in reverse will still push warm air along the ceiling to the walls/door, but a low speed "forward" may create a localised recirculation of warm/cool air that does not reach the walls?
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Re: Looking for a ceiling fan

Postby Tracker » Tue Jul 24, 2012 1:41 pm

Gordon-Loomberah wrote:That "normal practice" is completely unnecessary IMO, it really makes no difference if the warm air is blown down in the middle of the room and cold air moves up the walls, or the warm air moves down the walls- the aim is to mix the air and prevent stratification,

Interesting observations, Gordon, and consistent with my findings..
Our main heater is in the Family/Lounge room.. an Un-flued Gas heater. Cough :oops: Splutter :evil: Gasp
I positioned a simple personal fan to blow the heat at the Kitchen entrance, and it quickly heats to a comfortable temp., where it was always cold.
The side benefit, is that the entire Family-Room is now more evenly heated and more comfortable.
As you say - no heat stratification.
So, adding to your comment that it matters naught if the heat goes up or down, or around and around..IMHO

'Twood be interesting to do the sums on any fan (Ceiling or Portable), and work out the efficiency difference between pure DC/DC OR DC/Inverter and 240vAC motors..
12V is just a No-No in my mind.. ie total system efficiency.. but I understand the temptation of KISS 12Vdc..
..
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Re: Looking for a ceiling fan

Postby zzsstt » Tue Jul 24, 2012 2:01 pm

Tracker wrote:So, adding to your comment that it matters naught if the heat goes up or down, or around and around..IMHO


Not really. You're explicity pushing the air in one direction, towards a door, with a horizontal fan.

I have no doubt that the heat is distributed equally in the area of the fan, whether it is pushing air up or down. But over a longer distance I have found "up" works better for less fan effort.

Trying to explain without pictures:

Pushing the warm air down results in a doughnut of air circulation around the fan - vertically downwards below the fan, then out, then back up as the warm air rises back towards the ceiling. The size of this doughnut depends on the speed of air movement. With sufficient airflow the doughnut will encompass the entire room, but otherwise it won't. The fan is acting against the "thermo syphon" effect that would normally be in operation (centred on the heater).

Pushing the air up results in warm air trapped on the ceiling moving out to the walls. It keeps moving outwards until it reaches the walls, where the air following it causes it to be pushed downwards or through a doorway etc. The fan in this case is assisting, and in turn being assisted by, the flow of warm air up and out across the ceiling.

This is certainly what seems to happen in my room, but that may be because the fan is right in front of the wood burner and has a constant source of warm air to push along the ceiling?

I have no doubt that turning the fan to "high" and pushing air downwards would indeed circulate throughout the entire room, but it would also be noisy and uncomfortable to sit under! On "low" in reverse, it seems to achieve the same thing and the person under the fan is not subject to a blast of hot air!!
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Re: Looking for a ceiling fan

Postby Gordon-Loomberah » Tue Jul 24, 2012 2:36 pm

zzsstt wrote:Pushing the warm air down ... The fan is acting against the "thermo syphon" effect
...
Pushing the air up ...keeps moving outwards until it reaches the walls, where the air following it causes it to be pushed downwards


In the latter scenario the warm air is also being forced against its natural tendency to rise via convection, but only has air behind to push it, rather than a fan. If I was full of hot air, I think a fan would get me moving faster than a warm zephyr blowing from behind :lol:

The fan that was in the room with my heater had 5 speeds, the faster speeds moved the air right through the house, but the lower speeds kept the hot air well mixed in the louge room with no need for a big blast, although higher speeds certainly made it happen faster due to the extra turbulence.
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Re: Looking for a ceiling fan

Postby Tracker » Tue Jul 24, 2012 3:43 pm

Gordon-Loomberah wrote: the faster speeds moved the air right through the house, but the lower speeds kept the hot air well mixed in the louge room with no need for a big blast, although higher speeds certainly made it happen faster due to the extra turbulence.

I agree totally with the Doughnut flow with the ceiling, but I just found that anything that creates turbulence, seems to end up with the same result... as far as the Family Room was concerned (not that I could compare to a ceiling fan - none there)
Even the Doughnut flow is flawed in that the irregular room shape (not circular) will surely create grand eddies etc.
If I put dye in a bucket of water, it will quickly disperse whichever way I stir it, but one way might be slightly better..
Why, even the horizontal fan is going to create the old Doughnut but horizontally.. Can't help thinking we are making something scientific out of a non-issue..
zzsstt wrote:This is certainly what seems to happen in my room, but that may be because the fan is right in front of the wood burner and has a constant source of warm air to push along the ceiling?

Try just having a personal fan near the heater, on low, blowing down the room..
IMHO, I suspect you won't tell the difference in the room wrt the ceiling fan..
....It's just me - A bit weird in my thinking.. :?
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Re: Looking for a ceiling fan

Postby stivzor » Tue Jul 24, 2012 5:43 pm

zzsstt wrote:...acting as your personal Google proxy, a quick search for "12V ceiling fan" comes up (top of the list) with http://www.offgridaustralia.com/products/12v-dc-remote-control-ceiling-fan listed at just $275


Yes, expensive and ugly :-)

That is the only other one I can find that comes close to what I want, and I notice that someone is advertising it for $199 on eBay.

Al the discussion is interesting. Briefly in response:
- I am happy with very slow circulation; it's all I need and I would prefer to be able to run a low-powered DC device than have to turn on my inefficient inverter.
- The direction that the fan turns may not end up making a lot of difference in terms of air circulated, but it does make a difference in terms of people's impression of temperature. Having a downward flow of air feels colder.
- I have a lowish ceiling and would be happy with a fan that sits close to it.
- Postage from the US is prohibitive, so unless I can find a local distributor I may have to get this one: http://www.ebay.com.au/itm/12V-DC-Ceili ... 0832571656

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Re: Looking for a ceiling fan

Postby zzsstt » Tue Jul 24, 2012 6:20 pm

According to the green directory, a company called Eco-vibe (http://www.ecovibe.com.au) sell the Vari-Cyclone (http://www.survivalunlimited.com/ceilingfans.htm)in Australia, though it's not mentioned on their website. The Vari-Cyclone is hellish expensive overseas, so I can't imagine the cost over here. But I've read about it (couldn't find the links earlier) and apparently it has aerofoil shaped blades that actually work - not flat blades like most fans.....
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