Still interested in purely-radiant cooling.

Hi:
Please don't get upset at me. I posted something similar recently but it didn't describe it properly.
I thinking of a cooling mechanism for houses and building in which the cooling -- in the direct sense -- involves only radiation and no convection at all. Sorta like a radiant-stove-top in reverse. Indirectly, however, some amount of convection and conduction will be needed [liquid helium, cold metals]. The cooling panel is the ceiling and cools objects below it.
My visualization is that the radiant cooling panel contain extremely cold metallic coils [cooled by liquid helium to almost absolute zero], this would probably be deepest part of the panel.
http://en.wikipedia.org/wiki/Liquid_helium
Here, another question arises. Which is better to use -- Helium-3 or Helium-4? Which one would have a stronger cooling effect if both were at the same temperature?
The radiant cooling panel is the ceiling. It has 3 layers.
Layer 1: a material that allows heat radiation to pass through but is a very poor conductor of heat Layer 2: the same material found on the very top of radiant stove tops Layer 3: this is the deepest part containing the cool metallic coils. Inside these coils are where the liquid helium would be flowing through]
Layers 2 & 3 don't have any air molecules around them. The cold metal coils are in a vacuum so they are not exposed to any air that would solidify/liquefy. This means the space between layer 1 & 2 is also a vacuum free of air.
There is dehumidification which is separate from the cooling.
Dehumidification is done by air processing devices on walls -- left, right, back, front. These walls give out and take in air. There is both re-circulation and fresh air. For fresh air, all vapors molecules are let into the room -- excluding H20, CO2, gases with odors, toxic vapors [such as CO], dust, irritating vapors, smoke or allergens. For re-circulation, air in the room is sucked, cleaned [i.e. H20, CO2, toxic vapors [such as CO], dust, irritating vapors, smoke and allergens are removed] and then blown back into the room. In either case, the amount of air-molecules-per-second-per-square-meter that is sucked out of the room is the same is the amount of air-molecules-per- second-per-square-meter the is blown into the room -- and visa versa. Hence, the subject in the room doesn't feel any sucking or blowing.
The result is that the room now contains only N2 and O2 -- if you exclude the CO2 and H2O-vapor emitted from the living subject[s]. The N2 and O2 are kept at no less than least 70 degress Fahrenheit -- via convection heating if the ambient temperature is less than 70 F -- to prevent them from liquefying or solidifying. I know it's ironic that the air would have to be heated in order to assist in preventing the radiant cooler from failing. Still interesting, though.
Yes, heat absorbed into the radiant cooling panels is carried off using convection -- but this is not what the subject inside the room feels. The direct cooling effect on anything/anyone inside the room is radiant.
Can anyone suggest a better manner for direct radiant cooling? If so, please explain
By direct radiant cooling, I mean that if you place your body at a noticeable distance from from panel, you'll feel cold because the extreme cold of the coil will draw IR radiation away from your body. OTOH, if you touch the panel, you won't feel as cold because the 1st layer of the panel is a very poor conductor of heat.
On the ceiling, layer 1 is the lower than layer 2. Layer 3 is the highest.
Thanks a bunch,
Radium
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Maybe if you told us what the intended application is.....
I can't even visualize any application where it would be cost effective to use a system like that. Just the liquid helium would make it cost prohibitive.
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It is to keep a room comfortably cold during the summer.

Call me weird but I prefer my cooling to be directly-radiant and heating to directly involved natural convection of dry air. Just something about radiant cooling that gets my interests going.
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wrote:

Maybe you should be looking at a system that will cost less than the house its going into.
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wrote:

Not to mention such a system would instantly cause severe frostburn should any body parts come into contact with it.
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wrote:

Why would frostbite occur? The lowest layer [the one a body part would most likely contact] is an extremely poor conductor of heat, so it wouldn't feel that cold. It's the radiant cooling, that would feel cold.
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Sounds like you are describing something that is in every kitchen: a residential freezer. It too is very cold inside, but has "an extremely poor conductor of heat" (an insulator) on the outside "where it is most likely to come into contact" with any heat source.
How well does the outside wall of that freezer collect the heat radiated from your body when you are a few feet or even a few inches away?
While I think that innovation starts with "outside the box" thinking, I believe that it still must be based on the laws of THIS universe.
Bob

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On Sat, 16 Aug 2008 08:23:49 -0500, "Bob Shuman"

    No. It works primarily via convection. Even the old 'cold plate' fan-less ones ( as slow as they were to cool ).

    Once the heat is radiated from your body, it is gone ( to you ). It's not going to turn around and come back if it fails to find a place to go.
    Also, ;picture standing in front of a campfire - your face can get too hot, while your ass freezes.
    A very small percentaqe of the heat you radiate goes in any one particular direction, and the amount that falls on the 'receiving / absorbing surface' will thusly decrease as the square of the distance from it.

    Takes all the fun out of engineering .....

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Not if the surface completely encloses you. The MRT is solid angles weighted by their temperatures. Multiply each area your body sees by its temp, add the products, and divide by the total area of a reference sphere surrounding you, containing the individual areas. You might radiate 50% to a large close wall. As you walk away from a large wall, the near-field view factor might still be about 50%.
And we don't need liquid helium. The MRT graph here:
http://heatkit.com/html/guide2.htm#MasonryHeating
says we can be comfy in 90 F air with 40 F walls, in a bunny-free room.
Some buildings have chilled beams and ceilings for cooling. A chilled floor would make more sense, since warm air rises. A slow ceiling fan with an occupancy sensor and a room temp thermostat could stir up some floor air as needed for comfort.
Nick
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