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'[OT] Air circulation'
2004\12\22@203442 by Josh Koffman

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Ok, so my thermodynamics knowledge isn't so great. I have a room,
about 15' by 15', with a 10' ceiling. It's heated by a water filled
radiator.

My problem is this. Because the only air movement in the room is as a
result of convection, there isn't a whole lot of movement, and warm
air tends to congregate at the top of the room. I'd like to try and
pull some of that back down to keep me warmer. Installing a ceiling
fan isn't an option. I do have a few smaller (9") table top fans
though.

So the question is, would running these actually help? What would be
the best setup? Have the fans sitting low, blowing up? Try and put
them up on a shelf, even though they'll only be able to blow
horizontally, not down?

Any ideas?

Josh
--
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools.
       -Douglas Adams
____________________________________________

2004\12\22@211124 by Rolf

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Josh Koffman wrote:

{Quote hidden}

Put it in the middle of the floor, pointing directly up.

Rolf
____________________________________________

2004\12\22@212324 by Russell McMahon

face
flavicon
face
> ... air tends to congregate at the top of the room. I'd like to try and
> pull some of that back down to keep me warmer. Installing a ceiling
> fan isn't an option. I do have a few smaller (9") table top fans
> though.

Any fan will help somewhat. Consider building a long vertical tube and use
an available fan to suck or blow air down it from the ceiling. This way you
get concentrated warm coming down and diffused cold going up from the room
to replace it. If you blow cold up a tube you will push a diffuse layer of
warm down and probably get less noticeable effect. Top to bottom temperature
differential can be significant. Top bunks are warmer in winter - especially
so if they are above openings such as doors and windows and room insulation
is reasonable.


       RM

____________________________________________

2004\12\22@230918 by Mike Hord

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> Top bunks are warmer in winter - especially
> so if they are above openings such as doors and windows and room insulation
> is reasonable.

A fact which saw me through cold weather while in college in Fargo, ND.

Average year-round temp is ~40 degrees F (4.5 deg C).  I believe it's the
4th or 5th coldest city in the US.

Mike H.
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2004\12\23@065131 by Morgan Olsson
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face
I have here put fans on the radiator:

o Helps convection a lot: i can run me heat pump more economically.

o More volume but lower temp of air from radiator, thus less hot in ceiling, but warmer for me :)


For my grand mother i once made a "chimeny" with small fan sucking cold air from her cold floor, and throwing it up in the ceiling.  tHus warmer air approach the floor.  Really made the floor warmer.

/Morgan

Josh Koffman 02:34 2004-12-23:
{Quote hidden}

>_____________________________________________

2004\12\23@123951 by David Minkler

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face
Josh,

I worked in a factory (about 1200 sq ft. with 24 ft ceilings) that had
heaters mounted up high.  During the winter, it would get rather brisk
and the heaters just didn't seem to help much at all.  I realized that
we needed to stir the air so I took a fan, pointed it strait up near one
of the walls and turned it on.  Ten minutes later everybody was taking
their coats off and we ran the fan continuously every cold day from then
on.  The fan wasn't that large considering the size of the factory and
after we had started stirring the air we found we could run the fan at
low speed.  I'm pretty sure our heating bill dropped a little too.  It
just doesn't take that much to stir the air in a room.

If my experience is any indication, running just one of your table top
fans with it pointed as vertically as you can arrange (I'd put it near a
wall) will probably give you as much benefit in a room that size as any
other contraption you can arrange.  You are trying to stir the air up
and down.

Stay warm,

Dave

Josh Koffman wrote:

{Quote hidden}

2004\12\23@182406 by Andrew Warren

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face
Josh Koffman <spam_OUTpiclistTakeThisOuTspammit.edu> wrote:

> warm air tends to congregate at the top of the room. I'd like to
> try and pull some of that back down to keep me warmer. Installing a
> ceiling fan isn't an option. I do have a few smaller (9") table top
> fans though.
>
> So the question is, would running these actually help? What would
> be the best setup? Have the fans sitting low, blowing up? Try and
> put them up on a shelf, even though they'll only be able to blow
> horizontally, not down?

   The table fans will help a LOT.  Point them upward.

   If you ever do have a ceiling fan, the rule is to blow the air
   in the same direction as you want the temperature to go:  If
   you're cold and you want the temperature to go up, spin the fan in
   the direction that blows air upward.  If it's hot and you want
   to feel cooler, spin the fan in the direction that blows air
   downward.

   -Andy

=== Andrew Warren -- .....aiwKILLspamspam@spam@cypress.com
=== Principal Design Engineer
=== Cypress Semiconductor Corporation
===
=== Opinions expressed above do not
=== necessarily represent those of
=== Cypress Semiconductor Corporation

2004\12\23@223641 by p.cousens

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There are two types of radiator in common use in the UK, panel and
convector.
Convectors have extra fins (just a thin corrugated sheet spot welded to
the back of the panel rad)

This creates a series of chimneys that gives 50% more output per size
they also create bigger updraft
on the side the rad's on, and consequentially a far better air
circulation

Why not change the rad if it's just a panel
Or create your own chimney

PC

{Quote hidden}

2004\12\24@005947 by Russell McMahon

face
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face
> Convectors have extra fins (just a thin corrugated sheet spot welded to
> the back of the panel rad. This creates a series of chimneys that gives
> 50% more output per size

The "output" is entirely linked to the energy input unless there is a
thermostat which measures the temperature of the heater (not the air). A
finned heater will run cooler for the same energy input and give far better
convection, but two eg 1 kW heaters, one with fins and one without, will
both deliver the same energy to a room one way or the other if left to their
own devices. With heaters "what goes in must come out" applies.



       RM

2004\12\24@030142 by p.cousens

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Yes the same would also apply to fans or any other method
 PC

{Quote hidden}

2004\12\24@073325 by Howard Winter

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picon face
Russell,

On Fri, 24 Dec 2004 18:40:23 +1300, Russell McMahon wrote:

> > Convectors have extra fins (just a thin corrugated sheet spot welded to
> > the back of the panel rad. This creates a series of chimneys that gives
> > 50% more output per size
>
> The "output" is entirely linked to the energy input unless there is a
> thermostat which measures the temperature of the heater (not the air).

Yes, but the "input" for a water-filled radiator is related to the flow rate of the water (probably constant
unless there are radiator thermostats) and the temperature difference between the incoming and outgoing water
(flow and return as plumbers call it).  The heat given to the room by the radiator cools the water, and the
more efficiently it does this, the more heat is emitted and the cooler the return water for given flow and
room temperatures.

> A finned heater will run cooler for the same energy input and give far better
> convection, but two eg 1 kW heaters, one with fins and one without, will
> both deliver the same energy to a room one way or the other if left to their
> own devices. With heaters "what goes in must come out" applies.

Yes, but you're talking about "1kW" by which presumably you mean an electric heater (which must be almost 100%
efficient, since almost all of its energy turns to heat, which is what you want!) whereas we're talking about
central heating using water as the heat-carrying medium.  Water-filled radiators don't emit all the heat
they're given since the return water isn't at 0K :-)

Merry Christmas!


Howard Winter
St.Albans, England


2004\12\24@080813 by Josh Koffman

face picon face
Thanks everyone for the suggestions. Just to follow up, last night I
tried one of my fans, pointing up near one of the walls across the
room from the radiator. The rooms seemed noticable warmer after a
little while, so I think I'll use this on colder evenings. Of course,
the fact that I turn on two computers and a tv when I get home also
helps to heat up the room! Anyway, thanks again for everyone's input.
I think I've found a solution that works well enough for now!

Josh
--
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools.
       -Douglas Adams

2004\12\24@103622 by Peter L. Peres

picon face

On Wed, 22 Dec 2004, Josh Koffman wrote:

> Ok, so my thermodynamics knowledge isn't so great. I have a room,
> about 15' by 15', with a 10' ceiling. It's heated by a water filled
> radiator.
>
> My problem is this. Because the only air movement in the room is as a
> result of convection, there isn't a whole lot of movement, and warm
> air tends to congregate at the top of the room. I'd like to try and
> pull some of that back down to keep me warmer. Installing a ceiling
> fan isn't an option. I do have a few smaller (9") table top fans
> though.
>
> So the question is, would running these actually help? What would be
> the best setup? Have the fans sitting low, blowing up? Try and put
> them up on a shelf, even though they'll only be able to blow
> horizontally, not down?

Reverse flow is the most efficient way. This means finding out which way
the air is moving where you put the fan, and arranging for the fan to
blow against it. You can use a candle to find out the direction. You
could locate a large cardboard tube and put a fan in it (hidden). The
tube can stand vertically near the radiator or in a corner near it (it
can be square or triangular or whatever section). Arrange for the fan
volume to circulate the room air volume 2-3 times per hour. For example
a 100cfm fan is all you need for a 10x20x8 room. The best thing you can
do is to plate (temporarily) the exterior wall(s) with insulating
material. 1 layer of carboard tacked on will already improve things (on
account of the air space it forms behind it). Beware of fire proofing,
not just the cardboard. A fan motor catching fire will make enough smoke
to land you in hospital.

Peter

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