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Low cost, energy-saving radiative cooling system ready for real-world applications (edit: fixed link)
University of Colorado Boulder and University of Wyoming engineers have successfully scaled up an innovative water-cooling system capable of providing continuous day-and-night radiative cooling for structures. The advance could increase the efficiency of power generation plants in summer and lead to more efficient, environmentally-friendly temperature control for homes, businesses, utilities and industries.
The new research demonstrates how the low-cost hybrid organic-inorganic radiative cooling metamaterial, which debuted in 2017, can be scaled into a roughly 140-square-foot array—small enough to fit on most rooftops—and act as a kind of natural air conditioner with almost no consumption of electricity.
"You could place these panels on the roof of a single-family home and satisfy its cooling requirements," said Dongliang Zhao, lead author of the study and a postdoctoral researcher in CU Boulder's Department of Mechanical Engineering.
(Score: 3, Interesting) by Virindi on Sunday October 28 2018, @02:40PM (19 children)
Sure, you could have a reflector that bounces away IR, and you could also have a 'cold storage' which emits heat at night. Suppose you did this: you had a jar of water on your roof and during the day you placed a mirror over it. At night, you removed the mirror. It seems to me that because of the laws of thermodynamics, it is impossible for this invention to be better than if you did this?
Or, what if you just covered your whole roof with a layer of mirrors mounted a bit above the roof and then placed the jar under them in the shade? The jar would continue to radiate in the non-sun directions and only not do so directly above.
But what I don't understand, is how this could possibly be better than just having a radiator with water pumps that turn on at night and off during the day. You still need pumps with this proposed system because you have to get the cool water into the area to be cooled.
And of course they are trying to overhype their "invention", but we know that it is impossible for it to ever cool below minimum ambient. At least in the climate I live in, that would limit its usefulness to spring and autumn (or the magical "supplementary" use).
(Score: 2) by Bobs on Sunday October 28 2018, @04:13PM (15 children)
Tech sounds interesting.
Hope it turns into something cost effective and practical to use.
(Score: 2) by ledow on Sunday October 28 2018, @04:30PM (14 children)
I can do that. I put it under a sheet of opaque material and therefore put it out of direct sunlight in the shade, which will be cooler.
It's a rubbish claim, without some explanation of what it's doing and where the energy that would normally be there is going to.
(Score: 2) by Bobs on Sunday October 28 2018, @04:43PM (13 children)
I get that.
But given the time of day, location and time of year, most things will at least reach ambient temperature, even in the shade.
Things in direct sunlight will often be hotter than ambient air temperature, right?
Need more details, and time, to assess their claims, but it sounds like a decent experiment to test the system.
(Score: 4, Insightful) by grumpcuss on Sunday October 28 2018, @06:51PM (12 children)
After digging several layers deep to get the actual paper:
They are embedding specially designed silica spheres in a highly transparent film. The spheres are tailored to emit infrared black body radiation very efficiently, while the enclosing film absorbs very little light at any wavelength. The radiant energy will only depend on the absolute temperature of the material, independent of ambient temperature. The film is backed by a silver reflector to direct all radiation, emitted and incident, back into space. This makes it possible to actually cool below ambient, dependent on convective heat input.
So not necessarily bunk, nor overhype. More like Maxwell's demon.
(Score: 2) by Virindi on Sunday October 28 2018, @08:39PM (8 children)
So you are essentially claiming that they have reversed entropy (or they are claiming that)?
If it is possible to passively cool an object below ambient without any energy input, then the second law of thermodynamics has been disproved! Sweet!
In fact, it is equivalent to a perpetual motion device. All you have to do is place this material on one side of, say, a Seebeck plate, and a heat sink on the opposite side. The side with this material will be below ambient, and the heat sink will be at ambient. Thus, electricity will be generated. Out of nothing.
*sniff sniff* Wait, what is that smell?
(Score: 2) by The Mighty Buzzard on Monday October 29 2018, @02:23AM (7 children)
You really can't read very well, can you?
My rights don't end where your fear begins.
(Score: 2) by Virindi on Monday October 29 2018, @03:12AM (6 children)
Oooh Soylent. A driveby insult with absolutely no context or explanation.
The internet sucks :(
(Score: 2) by The Mighty Buzzard on Monday October 29 2018, @10:19AM (5 children)
Was there need? I mean it was pretty obvious to me that nobody was claiming to have reversed entropy, so either your reading comprehension or your physics sucks.
My rights don't end where your fear begins.
(Score: 2) by Virindi on Monday October 29 2018, @03:27PM (4 children)
It is you who is mistaken. Let us examine the post I was replying to.
The poster clearly describes a device which emits but does not absorb heat energy. The poster even cites Maxwell's Demon, a well known thought experiment posing this scenario. From Wikipedia: (https://en.wikipedia.org/wiki/Maxwell%27s_demon)
And I replied:
(Score: 2) by The Mighty Buzzard on Monday October 29 2018, @04:21PM (2 children)
Like I said, your reading comprehension sucks. There's a very important word in something you quoted that you're utterly ignoring or missing.
My rights don't end where your fear begins.
(Score: 2) by Virindi on Monday October 29 2018, @04:41PM (1 child)
Or maybe, just maybe, I comprehend exactly the words being written but you have a different interpretation?
I am no longer interested in responding to troll statements by someone who merely throws insults and refuses to explain his own arguments.
(Score: 3, Funny) by grumpcuss on Monday October 29 2018, @09:21PM
An open container of water will self cool to below ambient temperature (down to the dew point). Is this a reversal of entropy? The processes are analogous.
Any mass at a temperature above absolute zero will emit thermal radiation. That is established physics. That mass will also absorb incident radiation. The trick is to minimize the absorptive surface, while maximizing emission. That is what they have done.
As for your example of the Seebeck plate, the "warm" side of the plate will cool to equilibrium with the "cool" side as electricity is generated. The "heat sink" is a red herring. There must be energy input to maintain the "warm" side at temperature.
Before flaming about entropy reversal and such, you should learn a bit more thermodynamics. And try reading and understanding the research. I did.
And I never said it actually WAS Maxwell's demon, I simply made the comparison that it was more similar to that than to "bunk, or overhype". This actually has a chance at working.
You may now return to your bridge.
(Score: 0) by Anonymous Coward on Tuesday October 30 2018, @09:40PM
You're thinking about the wrong ambient temperature. The key word is "space." Space is, on average, cold [vif.com] (pdf) at around 3 K. Because we're near the Sun, and because the albedo of the Earth is less than unity, and because of the atmosphere, we're not so cold. The dark side of the Moon gets cold, and craters near its poles are always cold. The effort here is to work around the effect of the Earth's atmosphere.
(Score: 2) by c0lo on Sunday October 28 2018, @10:21PM (2 children)
Cool below ambient? No.
Start below ambient and keep it cooler in a non-equilibrium with the environ? Yes, but this is nothing new - Dewar bottles exist for ages already.
The only technological advance that I see is not using a double-wall-with-vacuum to implement it.
https://www.youtube.com/watch?v=aoFiw2jMy-0
(Score: 0) by Anonymous Coward on Tuesday October 30 2018, @09:49PM (1 child)
A dewar insulates. It minimizes heat transfer by conduction, radiation, and convection. A well-insulated building is like a dewar. This is very different. The idea is to transfer heat away from a structure by radiating it to outer space.
(Score: 2) by c0lo on Wednesday October 31 2018, @05:15AM
If the space radiates back with the same intensity, that will do nothing - the outgoing and the incoming radiant flux will cancel.
Unless you managed to create the "thermal diode", that is.
https://www.youtube.com/watch?v=aoFiw2jMy-0
(Score: 0) by Anonymous Coward on Tuesday October 30 2018, @09:07PM
we know that it is impossible for it to ever cool below minimum ambient
Others working in this field placed an object in an insulated box with a window pointing toward the sky. They attached their similar film to the top of the object. They say that the temperature of the object fell below the ambient temperature. I don't remember clearly, but I understood it as meaning below the minimum ambient temperature. Wouldn't the theoretical minimum, for the arrangement I described, be the temperature of the cosmic background radiation? That's around 3 kelvin. Ambient temperatures on Earth are around 300 kelvin.
(Score: 0) by Anonymous Coward on Tuesday October 30 2018, @09:24PM
Thisis a press release about another effort. They claimed "nearly 9 degrees Fahrenheit cooler than the surrounding air during the day." I don't know the physics behind it, but we can make emitters of light that don't approximate black bodies. If it's no more effective than providing shade from sunlight during the day and a view of the sky at night (something that could be done without a moving mirror) that will be a disappointment, but easy to check. [stanford.edu]
(Score: 0) by Anonymous Coward on Tuesday October 30 2018, @11:56PM
They were doing that, but with straw instead of mirrors, in Iran in the 5th Century BC. https://web.archive.org/web/20170218184105/http://misfitsarchitecture.com/2013/02/22/its-not-rocket-science-2-yakhchal/ [archive.org]