Half a croissant, on a plate, with a sign in front of it saying '50c'
h a l f b a k e r y
Assume a hemispherical cow.

idea: add, search, annotate, link, view, overview, recent, by name, random

meta: news, help, about, links, report a problem

account: browse anonymously, or get an account and write.



Radiator Fans

Make radiators more efficient
(+3, -3)
  [vote for,

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.
goff, Oct 20 2003

Stirling Powered Fans http://www.thermalengines.com/index.html
one of a few manufacturers [Laughs Last, Feb 16 2009]


       I've seen these homemade. I don't know if they exist commecially.
phoenix, Oct 20 2003

       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.   

       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.
suctionpad, Oct 20 2003

       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).   

       If the drive train is light, you could use the flow of the hot water itself to run the fans.
phoenix, Oct 20 2003

       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?
swamilad, Oct 21 2003

       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.
goff, Oct 21 2003

       [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.
suctionpad, Oct 21 2003

       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.
John_T, Jan 08 2004

       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.   

       Bonus: you could put some lights in your radiator as well!
choiski, Apr 13 2004

       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.
RockyLSU, Apr 27 2004

       If you are worried about loss through the wall, why not just move your radiator to the middle of the room?   

       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.
Loris, Apr 28 2004

       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.   

       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)?   

       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.
haverwench, Nov 06 2006

       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.   

       This method of heating is used in many apartment buildings that have a centrally located heating and cooling system.
Jscotty, Nov 07 2006

       Get some small fans and put them in the radiator cover and power them a la radiator booster product.
PhillInSkeg, Feb 13 2009

       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.   

       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.   

       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.   

       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.   

       4) Drafty air makes you feel colder unless it is very hot.
WcW, Feb 13 2009

       //Radiator systems are called radiators beacuse they warm by radiation, warming you WITHOUT warming the AIR.//   

       You might assume that, but you'd be wrong.   

       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."   

       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!   

       Electric bar heaters on the other hand, do function mainly by radiation. But we're not talking about those.
Loris, Feb 15 2009

       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.   

       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.   

       [1] To be pedantic, not even then, until the room contents reaches the same temperature.
Loris, Feb 15 2009

       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.
WcW, Feb 16 2009

       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.   

       Do you want me to spell it out? I could put spaces between the letters.
Loris, Feb 16 2009

       simply put I think that you are wrong.
WcW, Feb 16 2009

       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?
Loris, Feb 19 2009

       nope, just trying to keep things succinct.
WcW, Feb 19 2009

       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.   

       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.   

       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.   

       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.   

       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.   

       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)   

       So with a Hot water system the effect is even less.   

       Perhaps if I had the time I could find a calculation in excel that would do it accurately.   

       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.
benhadad, Nov 11 2010

       Sorry links below are broken up. www.engineeringtoolbox.com/ heat-emission-radiators-d_272 .html   

       www.engineeringtoolbox .com/heat- emission-radiators-d_1121.html   

       en.wikipedia.org/wiki/ Stefan%E2%80%93 Boltzmann_law   

       www.ashraenbpei.com/ hydronic_heating.html docs.engineeringtoolbox. com/documents/431/ heat_radiation_ from_black_ surface_to_unheated.png
benhadad, Nov 11 2010

       If you're increasing airflow against an outside wall then you're increasing the thermal conductivity of the wall.
FlyingToaster, Nov 11 2010


back: main index

business  computer  culture  fashion  food  halfbakery  home  other  product  public  science  sport  vehicle