h a l f b a k e r yIncidentally, why isn't "spacecraft" another word for "interior design"?
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Radiators - they radiate. as much heat hits the wall as the room. Half of it goes up behind the curtains. You can improve it - my radiators are painted matt black (best colour for radiation) and housed in covers which are lined with tin foil. Most of the heat comes out of the vents in the front.
BUT....you
could heat up the room much quicker if you had fans in the top of the radiator cover which drew air up past the radiator and pumped it out into the room, in much the same way as a fan heater blows air across the element. The trick would be to make the fans really quiet, so they did not disturb your tv watching/book reading etc. and economical so they used very little energy.
Alas, my idea is truely half baked. I cannot think of a really innovative way of powering the fans. I kept trying to think of some way of using the heat from the radiator itself, but if you just used the convection current for example, the fans would spin, but just slow up the air that was already moving rather than propel it forward. Bright ideas welcome.
The default would be small, quiet electric fans - I don't envisage them blowing hard like a fan heater, just increase the effieciency of warming up the room by drawing cold air in from the bottom and pumping it past the radiator and out the top.
Stirling Powered Fans
http://www.thermalengines.com/index.html
one of a few manufacturers [Laughs Last, Feb 16 2009]
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I've seen these homemade. I don't know if they exist commecially. |
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It wouldn't take much airflow to increase heat transfer rates and to circulate the heat through the room. You could run your electric fans from thermovoltaic cells, although I imagine this would be a bit expensive. |
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Or you could run the fans from Stirling engines. Quiet and efficient, although I wouldn't be able to do the sums to see if the energy you need is there. |
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Note that the heat isn't exactly going to waste now. It's simply being recycled. The only thing the fan does is increase the rate at which the room will warm initially. The fan won't make the system more efficient (as near as I can tell). |
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If the drive train is light, you could use the flow of the hot water itself to run the fans. |
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Also, electric radiators. They suck, but they're out there. What about them? Yes there is electricty there that could be used to run fans, but that doesn't really seem like the halfbakery solution to me. Likewise if you were going to use regular line voltage to power these fans, don't most radiator's have it nearby anyway? |
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Actually phoenix, I think it will make it more efficient, as by drawing cold air in at the bottom and passing it over the radiator, more heat will go into heating the air, rather than say the wall behind (even if covered with foil), as the temperature diff is greater between the air and the radiator than it would be if it was static - therefore the air acts as water does in a car engine, taking heat away from the hot bits (the radiator) and being pumped out into the room. |
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[goff] don't forget that the increase in airflow will increase heat transfer coefficients (that is the rate at which heat can be transferred from one region to another). Changing the heat transfer regime from free convection to forced convection by purposely blowing air across the surface of the radiator could give an order of magnitude increase in the rate of heat transfer from an area of the radiator which heats the room, reducing % wasted heat. |
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I've used this idea for years. It
definitely works, I just use a
window fan that has a particularly
quiet, low-speed. The room I do
this in is my work/computer room,
and also the house's thermostat is
in this room. I'm able to set the
thermostat lower, but it thinks the
whole house is warm.....the rest of
the house gets cold while I do this,
but I've knocked about 40% off my
natural gas bill. |
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Here's my idea:
Buy a small USB hub and two USB fans like the Kensington Fly Fan. You could probably do the whole thing for about 30 bucks. |
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Bonus: you could put some lights in your radiator as well! |
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Why not instal a ceiling fan that why it will stir the air in the room one way in the summer cooling the room down and then you could switch it over to rotate the in the opposite direction in the winter helping to warm the house up. Sweet and Simple plus dual purpose. |
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If you are worried about loss through the wall, why not just move your radiator to the middle of the room? |
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Incidentally, I believe radiators transfer most of their heat by convection already. The air close to them heats up, rises and is replaced by colder air. |
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I've wondered about this myself.
According to the Wikipedia entry on
"radiator," you can now get radiators
with built-in electric fans, but this is no
help to those of us who have old steam
radiators and want to improve their
efficiency. I do know that a similar
device already exists to help spread the
heat from a woodstove (see http://
www.gyroscope.com/d.asp?
product=ECOFAN). It uses the "Peltier
effect" to power the fan using the
stove's own heat. According this site,
the fan will turn slowly if you set it on a
hot radiator, but it's not clear whether it
will turn fast enough to distribute the
heat effectively. |
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Query for John T: do you set the fan
blowing away from the radiator or
toward it (to drive cold air under the
radiator and speed up the convection
process)? |
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And for Loris, a note: I can't answer for
goff, but the reason I can't move my
radiators to the middle of the room is
that they're single-pipe steam radiators
connected to the plumbing in the walls. |
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Already baked- McQuay makes radiator/fan units that mount on the floor against wall where a traditional radiator would normally be. You can actually swap out your traditional radiator for one of these units and then run an AC line to it in order to power the fan. |
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This method of heating is used in many apartment buildings that have a centrally located heating and cooling system. |
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Get some small fans and put them in the radiator cover and power them a la radiator booster product. |
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1) Actually it's more effective to think about heating AIR in
terms of a loop of some sort. If you percieve that the air on
one side of the room is not being heated effectively it will
be more effective to concentrate on moving that air to the
heater rather than trying to make the heater flow more air
in the hopes that that air will move to the cold part of the
room. |
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2)Radiator systems are called radiators beacuse they warm
by radiation, warming you WITHOUT warming the AIR.
Putting a box around them completely defeats this! You
can dramatically improve the efficiency of radiators by
moving obstructions between the human spaces and the
surface of the radiator and putting reflectors behind the
units. Keeping the units clear also increases airflow
increasing the degree to which convection will circulate
warm air. |
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3) If you aren't getting enough heat from
an antique style cast radiator it is likely due to the
presence of trapped air in the radiator itself, or clogging.
Usually the problem with radiant heat is not inadequate
radiators but that it roasts you with radiant heat before
the air is hot enough to switch the thermostat. |
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3) Converting a radiant system to a forced air heating
system may well REDUCE COMFORT AND EFFICIENCY. Don't
be suprised if it takes longer to reach a comfortable
temperature or that you will loose more heat to leaks ,
open doors, and unused rooms. |
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4) Drafty air makes you feel colder unless it is very hot. |
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//Radiator systems are called radiators beacuse they warm by radiation, warming you WITHOUT warming the AIR.// |
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You might assume that, but you'd be wrong. |
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From 'Radiator' on Wikipedia:
"One might expect the term "radiator" to apply to devices which transfer heat primarily by thermal radiation (see: infrared heating), while a device which relied primarily on natural or forced convection would be called a "convector". In practice, the term "radiator" refers to any of a number of devices in which a liquid circulates through exposed pipes (often with fins or other means of increasing surface area), notwithstanding that such devices tend to transfer heat mainly by convection and might logically be called convectors." |
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If you think about it, because they're water heated, they're below 100 degrees C - usually well below. Black body radiation rises as the 4th power of absolute temperature, so you're looking at 400^4/300^4 or about three times what the room is radiating back. That isn't very much! |
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Electric bar heaters on the other hand, do function mainly by radiation. But we're not talking about those. |
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WcW, what you seem to have missed is that I didn't say heat transfer by radiation doesn't occur - I said it wasn't the majority effect. |
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You also haven't absorbed relevance of that figure properly - it's not a tripling of IR radiation in the room unless your radiator _encases_ the room[1]. Which does lead on to the underfloor heating you mentioned. It is, however, obvious the idea is not about those. So we're talking about those little metal jobs up against the walls. They're pretty obviously designed to promote convection. Funny that. |
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[1] To be pedantic, not even then, until the room contents reaches the same temperature. |
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My experience with radiant heating, tube radiators, and radiant stoves is that they all function in the same fashion. A tube radiator is called a radiator because radiation is the primary mode of action. By radiating the heat to other objects the air in the room is rapidly heated. I hope that instead of taking offense you will look again at your assumptions about how this works. When radiant heat first came into vogue the fact that it functioned without moving air was seen as a major feature. |
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Dude, we're talking about different things. It's obvious what sort of radiator goff has: if half the heat "goes up behind the curtains", it's due to convection. Talking about underfloor heating &c is irrelevant. |
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Do you want me to spell it out? I could put spaces between the letters. |
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simply put I think that you are wrong. |
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I see you've deleted a post above, which is pretty much an admission that it was in error. Maybe you actually read what I'd written? |
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nope, just trying to keep things succinct. |
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Please look at the following references:
Here is a typical calculation for the heat
release from a radiator (water). Notice it
doesn't distinguish how it given off whether by
"radiation" or by convection. |
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But engineers know the answer - based on this
law you can calculate with the delta T and the
surface area how much energy would be by
radiation. |
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This is determined by the emissivity,
Stefan-Boltzmann constant is used to calculate
it, as M = εσT4, based on this we can
actually
figure out if the unit will be receiving heat via
radiation or giving it off. |
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According to this chart a 1 SQ Meter (apx
10sqft) surface at 100C (close to steam systems)
with 20C (Cool room) would give you about 700
Watts of heat given off. Steam radiators are
normally size at 240BTU per Square foot (or
240x10.7=2600 BTU /SQMT) BTU to Watt
conversion will mean about 760 Watts given off
by this convection. |
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So the convection of this system is about 55% of
the total. And here we are basically using an
ideal radiator. In reality it is over 75% via
convection. The rest via conduction (touching
surfaces) and radiation. |
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The Stefan–Boltzmann law states that the
effectiveness of a thermal radiator is
proportional to the fourth power of its absolute
temperature. A hot-water radiator at 77 °C (350
K) has only 1/4 the emissive power of a stove at
220 °C (493 K), or 1/16th that of a radiant
element at 427 °C (700 K) |
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So with a Hot water system the effect is even
less. |
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Perhaps if I had the time I could find a
calculation in excel that would do it accurately. |
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For your information the above may have some
errors I state this as I am a Professional
Mechanical Engineer who designed
steam/hydronic systems in the past, but I have
forgotten some of the exact Heat Transfer calcs
that might impact the estimates. |
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Sorry links below are broken up.
www.engineeringtoolbox.com/
heat-emission-radiators-d_272
.html |
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www.engineeringtoolbox .com/heat-
emission-radiators-d_1121.html |
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en.wikipedia.org/wiki/
Stefan%E2%80%93
Boltzmann_law |
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www.ashraenbpei.com/
hydronic_heating.html
docs.engineeringtoolbox.
com/documents/431/
heat_radiation_
from_black_
surface_to_unheated.png |
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If you're increasing airflow against an outside wall then you're increasing the thermal conductivity of the wall. |
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