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post #1 of 10 (permalink) Old 12-20-14, 06:27 PM Thread Starter
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Default Zero-energy air conditioning

Sometimes it's like you looked at knives and bread for years. Sliced bread seemed so obvious in retrospect.

(Not a physicist, summarizing my best)
So, a material 'radiates' photons according to its color (duh). Some photons go through our atmosphere. Some get captured by greenhouse gases and thus 'retain heat'.

They made a material that was mostly ("nearly entirely") reflective to normal sunlight and to 'normal' IR wavelengths we see in the atmosphere, but of a heat-radiating color that the atmosphere doesn't capture very well. So, what happens is that the ambient heat doesn't enter the material very easily, but it radiates heat in a wavelength that the air doesn't them capture.

The net result? A material that's actually cooler than the air around it.

Apologies for the poor size of the graph. The blue (I think, I'm colorblind) line is the temperature of the film. The black line is the temperature of the air.





Passive radiative cooling below ambient air temperature under direct sunlight

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When exposed to direct sunlight exceeding 850 watts per square metre on a rooftop, the photonic radiative cooler cools to 4.9 degrees Celsius below ambient air temperature, and has a cooling power of 40.1 watts per square metre at ambient air temperature. These results demonstrate that a tailored, photonic approach can fundamentally enable new technological possibilities for energy efficiency. Further, the cold darkness of the Universe can be used as a renewable thermodynamic resource, even during the hottest hours of the day.
So, my commentary. I think my description is correct. And, if I'm figuring correctly, if they can learn how to make the 'bottom' black (so that it absorbs all incoming photons) and keep the upside 'reflective', something like this could go onto the surface of buildings and would actually siphon heat from the inside of a building and shoot it into space?

Wealth is created when we use new knowledge to create new things or improve efficiencies.
This technology, along with people pondering applications using type three levers is literally a new mechanical revolution in waiting. There are going to be many patents, from people who're curious and can tinker.

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post #2 of 10 (permalink) Old 12-23-14, 06:11 AM
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I'm not sure about the zero energy thing, as it does violate a law of thermodynamics.

But it is a cool thing that could have practical uses.
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post #3 of 10 (permalink) Old 12-24-14, 10:58 PM Thread Starter
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That's why I thought it was so nifty. It actually doesn't violate any laws of thermodynamics (it could hardly get published in Nature, one of the world's leading science journals if it did). I just really violates our normal intuitions!

Wealth is created when we use new knowledge to create new things or improve efficiencies.
This technology, along with people pondering applications using type three levers is literally a new mechanical revolution in waiting. There are going to be many patents, from people who're curious and can tinker.

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post #4 of 10 (permalink) Old 12-26-14, 02:05 PM
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Originally Posted by Reaper45 View Post
I'm not sure about the zero energy thing, as it does violate a law of thermodynamics.

But it is a cool thing that could have practical uses.
I think it means that it doesn't use any input from us in the forum of electricity or something similar.

Though I do think this sounds like a load of bollocks. The way things cool down, as I understand it, is that they transfer the heat they contain into something else. If this thing doesn't absorb any energy from the surrounding atmosphere then how is it "radiating heat" afterwards? It sounds like a load of pseudo-scientific garbage, so as I don't have the expertise to properly debunk but it seems like a load of shite, I'll believe it when I see it (published in a scientific journal).

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post #5 of 10 (permalink) Old 12-26-14, 03:44 PM
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Originally Posted by Silens View Post
...Though I do think this sounds like a load of bollocks. The way things cool down, as I understand it, is that they transfer the heat they contain into something else. If this thing doesn't absorb any energy from the surrounding atmosphere then how is it "radiating heat" afterwards?...
I don't know if it's bullshit or not but the concept of radiating heat without absorbing heat from light energy isn't bogus.

Think of a white material or a mirror in the sun. They reflect a lot of the light/heat energy and remain cooler. A good example is the white or silver coating on a flat rubber roof. The rubber and tar is naturally black and world absorb most or all of the light-heat directed against it. The white our silver reflects more of that energy.

However, Just because a mirror reflects most of the light doesn't mean that you couldn't heat the mirror itself. Once the mirror is warm it will radiate hear from its surfaces. So the heat transfer rate (add I understand it) will be based on the physical properties, the amount of surface area, and the ambient surrounding temperature.

So all of that said, the article appears to be saying that somebody invented a material that radiates heat faster than it absorbs heat from light shining on it.

Edit: just read the abstract. Actually they are talking about 2 separate functions of a system designed to radiate heat and cool a building. By adding the reflective coating it drastically reduces heat absorbed from the sun during the day allowing it to contribute radiating(cooling) at higher rate.

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post #6 of 10 (permalink) Old 12-26-14, 03:48 PM
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I don't know if it's bullshit or not but the concept of radiating heat without absorbing heat from light energy isn't bogus.

Think of a white material or a mirror in the sun. They reflect a lot of the light/heat energy and remain cooler. A good example is the white or silver coating on a flat rubber roof. The rubber and tar is naturally black and world absorb most or all of the light-heat directed against it. The white our silver reflects more of that energy.

However, Just because a mirror reflects most of the light doesn't mean that you couldn't heat the mirror itself. Once the mirror is warm it will radiate hear from its surfaces. So the heat transfer rate (add I understand it) will be based on the physical properties, the amount of surface area, and the ambient surrounding temperature.

So all of that said, the article appears to be saying that somebody invented a material that radiates heat faster than it absorbs heat from light shining on it.
Fair point. Like I said, I don't know enough to debunk it properly and I will remain skeptical until I see it in a scientific journal.

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post #7 of 10 (permalink) Old 12-26-14, 03:52 PM
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It is in a scientific journal. Nature is a major peer reviewed journal.

Conceptually the idea seems sound. Like you I don't know enough about the materials science the confirm or deny their findings.

Chaos Army Showcase with photos (Updated 2013/12/02)
"To endure one's self is perhaps the hardest task in the universe." Frank Herbert, 'Dune Messiah'
Quote:
Originally Posted by Dethklokk
"CHEESE!" is the battlecry of the ill-prepared.

Originally Posted by Deathscythe4722
Could someone please call the police on this guy? I can hear the English Language screaming in pain. This has to be illegal somewhere.
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post #8 of 10 (permalink) Old 12-26-14, 04:52 PM
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It is in a scientific journal. Nature is a major peer reviewed journal.

Conceptually the idea seems sound. Like you I don't know enough about the materials science the confirm or deny their findings.
Oh, I must've misread? I thought I read someone saying something like "I'll believe it when I see it in Nature".

If that's the case then bollocks to what I said, this is awesome.

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post #9 of 10 (permalink) Old 12-26-14, 05:20 PM
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Gotcha. =) It's all good.

The OP's second post said something like that but phrased in negative language.

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Originally Posted by el_machinae View Post
That's why I thought it was so nifty. It actually doesn't violate any laws of thermodynamics (it could hardly get published in Nature, one of the world's leading science journals if it did). I just really violates our normal intuitions!

Chaos Army Showcase with photos (Updated 2013/12/02)
"To endure one's self is perhaps the hardest task in the universe." Frank Herbert, 'Dune Messiah'
Quote:
Originally Posted by Dethklokk
"CHEESE!" is the battlecry of the ill-prepared.

Originally Posted by Deathscythe4722
Could someone please call the police on this guy? I can hear the English Language screaming in pain. This has to be illegal somewhere.
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post #10 of 10 (permalink) Old 12-27-14, 03:14 PM Thread Starter
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The link url goes straight to nature.com!

I tried to explain to my dad how this works, but he couldn't get past how confounding he found the entire idea was. It's a bit of a physics head-scratcher until you get it, it motivated me to rethink how I thought some of these principles.

Wealth is created when we use new knowledge to create new things or improve efficiencies.
This technology, along with people pondering applications using type three levers is literally a new mechanical revolution in waiting. There are going to be many patents, from people who're curious and can tinker.

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