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Earth Science

Professors Claim Passive Cooling Breakthrough Via Plastic Film (sciencemag.org) 203

Posted by EditorDavid from the cool-films dept.
What if you could cool buildings without using electricity? charlesj68 brings word of "the development of a plastic film by two professors at the University of Colorado in Boulder that provides a passive cooling effect." The film contains embedded glass beads that absorb and emit infrared in a wavelength that is not blocked by the atmosphere. Combining this with half-silvering to keep the sun from being the source of infrared absorption on the part of the beads, and you have a way of pumping heat at a claimed rate of 93 watts per square meter.
The film is cheap to produce -- about 50 cents per square meter -- and could create indoor temperatures of 68 degrees when it's 98.6 outside. "All the work is done by the huge temperature difference, about 290C, between the surface of the Earth and that of outer space," reports The Economist.
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Professors Claim Passive Cooling Breakthrough Via Plastic Film More

Professors Claim Passive Cooling Breakthrough Via Plastic Film

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  • This seems to be an incredible invention that will be a game changer. Passive cooling on the order of what this article talks about would seem to be too good to be true. If it is true these guys should be filthy rich soon.

    • "Passive cooling on the order of what this article talks about would seem to be too good to be true. If it is true these guys should be filthy rich soon."

      Don't forget to sell your Air Conditioning stock.

      • Re:Too good to be true. (Score:4, Insightful)

        by Mr D from 63 ( 3395377 ) on Sunday February 26, 2017 @12:20PM (#53933635)

        "Passive cooling on the order of what this article talks about would seem to be too good to be true. If it is true these guys should be filthy rich soon."

        Don't forget to sell your Air Conditioning stock.

        Its interesting that they have made the film, yet have not demonstrated it in a practical application. That makes me skeptical as they are relying on performance claims when they shouldn't have to. Why could they not take the film and cover a small structure (like a shed), and simply tell us the resulting cooling effect? And maybe compare against a simple reflective coating

        • >Its interesting that they have made the film, yet have not demonstrated it in a practical application. That makes me skeptical as they are relying on performance claims when they shouldn't have to. Why could they not take the film and cover a small structure (like a shed), and simply tell us the resulting cooling effect? And maybe compare against a simple reflective coating

          They have a peer-reviewed article published in "Science", other Researcher's have published papers on the same effect using difference materials and the "The Economist" article shows the Researcher's holding a big-ass roll of the stuff, there isn't much to be sceptical of.

      • I wouldn't sell it just yet. Even if this film works, it's probably only in clear conditions when the IR radiation can escape to outer space. On muggy cloudy or hazy days, I doubt it would work. On top of that, it would do nothing to lower the humidity in the building.

        • Re: (Score:2)

          by AJWM ( 19027 )

          True, but these guys are in Colorado. We get maybe a dozen cloudy or hazy days a year. And it's a semi-desert, no muggy days.

          Yeah, it might not work so well in the Mississippi valley region.

          OTOH, if they're shifting to a frequency of infrared not absorbed by H2O, it might not care about puny water vapour.

        • Wow, try reading....

          "At the same time, the film sucked heat out of whatever surface it was sitting on and radiated that energy at a mid-IR frequency of 10 micrometers. Because few air molecules absorb IR at that frequency, the radiation drifts into empty space without warming the air or the surrounding materials, causing the objects below to cool by as much as 10C. "

          • The problem being? It makes sense if you forgive a frequency given in units of wavelength.

          • That may be true for *air*, but if you look up the absorption spectrum for liquid water and ice (as found in clouds), it blocks 10um wavelength very well.

        • On muggy cloudy or hazy days, I doubt it would work

          Even if the cloud absorbs the IR, it's already out of the building you want to cool, so it has already served its purpose.

          • The effect depends on the fact that outer space doesn't radiate much at those frequencies.

            Under clouds there is more of a thermal equilibrium. So there will be about as much IR energy in that band being emitted from clouds and entering the building as leaving it. It's the same reason that cloudy nights usually stay warmer than clear nights.

          • Re:Too good to be true. (Score:5, Informative)

            by Rei ( 128717 ) on Sunday February 26, 2017 @04:49PM (#53934793) Homepage

            It doesn't work like that. Radiative heating/cooling works via exchange of IR. You're not just giving it up; everything you're radiating at is proportionally radiating back at you. So you cool the most when you're radiatively exchanging with something that's very cold. Aka, you want to be radiatively exchanging with the cosmic microwave background, not with low-altitude clouds. That's the whole point of radiating at low absorption frequencies in the atmosphere: so that you're exchanging with space, not with atmospheric air.

    • Not as hardcore as an active cooling by a gas dynamic laser.

      Most notable about this material is that it does not do heat pumping, just tricks with reflectivity and selective absorbtion, and emission bands

    • Re: (Score:2)

      by Kjella ( 173770 )

      This seems to be an incredible invention that will be a game changer. Passive cooling on the order of what this article talks about would seem to be too good to be true. If it is true these guys should be filthy rich soon.

      Well the article certainly lacks critical sense:

      And because it can be made cheaply at high volumes, it could be used to passively cool buildings and electronics such as solar cells, which work more efficiently at lower temperatures.

      Cool solar cells.... by blocking the sunlight *facepalm*. Also I'm thinking how big a deal is the "not blocked by the atmosphere" really, I mean it's not like heat reflected of a little building significantly changes the ambient temperature. And finally production cost is one thing, but how it works in real dust-covered conditions and if it can survive being exposed to the weather all year long is another matter. I don't think it's quite as revolutionary as th

      • Re:Too good to be true. (Score:5, Insightful)

        by DamonHD ( 794830 ) <d@hd.org> on Sunday February 26, 2017 @12:40PM (#53933681) Homepage

        It's called physics, even if you don't find it interesting.

        1) Letting visible light through in principle lets the PV work while keeping it cool. The increase in output with lower temperatures is quite significant, thus the presence on the market of combined PV/Thermal panels for example. (And absorbing more of the visible light and removing the energy as electricity rather than letting it turn into heat would be good too, natch, and that one is being worked on.)

        2) Outer space is at ~3K/-270C: having that as your cold sink *day and night* is really quite significant. What I cannot work out is if clouds are transparent at the same wavelengths, eg if this could be used to make the cold end of a Seebeck device even under cloudy skies: that would allow a small amount of power generation day and night also, if so.

        This looks plausible to me and and an astonishingly good thing if it works even a 1/10th as well as the researchers hope.

        Sometimes the science is good before the marketing people get to it.

        Rgds

        Damon

        • Re:Too good to be true. (Score:4, Informative)

          by lgw ( 121541 ) on Sunday February 26, 2017 @01:29PM (#53933877) Journal

          Outer space is at ~3K/-270C: having that as your cold sink *day and night* is really quite significant.

          Radiative cooling doesn't work that way: all that matters is your temperature. You don't radiate more into a cold area than a hot (a hot area sends more thermal radiation to warm you up, but that's orthogonal). It would be different if the atmosphere reflected IR, but that's not the case.

          • Re: (Score:3)

            by skids ( 119237 )

            It would be different if the atmosphere reflected IR, but that's not the case.

            Not in the sense of a mirror, but yes, it does, nondirectionally. More importanty, it tends to radiate at frequencies not absorbed by the material.

            • Re: (Score:3)

              by lgw ( 121541 )

              Not in the sense of a mirror, but yes, it does, nondirectionally. More importanty, it tends to radiate at frequencies not absorbed by the material.

              Look, "reflection" is a specific concept, OK? It's a different thing than absorption and emission. They are two different effects, which is why we use different words to describe them. There is some refraction by clouds, and I'm sure some trivial percentage is refracted multiple times to end up headed back towards the surface, but that's about it.

              Why does the distinction matter? Actual reflection of IR nearly blocks radiative cooling (at some point the reflective surface, not being perfect, heats up and

              • Re: (Score:3)

                by skids ( 119237 )

                Changing the frequency of your thermal radiation a bit will not make a meaningful difference in cooling.

                It is a bit backwards to phrase this as "beaming heat into cold space" rather than "reflecting most incoming ambiently-produced IR radiation while selectively emitting radiation in a same band we absorb" This doesn't seem to be the fault of journalists, it's phrased that way in the paper. This article [scitation.org] avoids using that semantic.

                Were they to allow the wavelengths re-emitted by the general environment outside, you'd get an offsetting absorptive heat gain. They could likely get the same effect at different

        • ~ -0.44%/degC

      • Cool solar cells.... by blocking the sunlight *facepalm*.

        No. It seems you missed the part in the article where they said you'd first need to remove the mirror backing in order to use it with solar cells. I.e. It would let (nearly) all of the light through while still providing the heat dissipation properties.

        Also I'm thinking how big a deal is the "not blocked by the atmosphere" really, I mean it's not like heat reflected of a little building significantly changes the ambient temperature.

        I take it you're unaware of urban heat islands [wikipedia.org]?

        Controlling how light and heat get reflected from buildings is of growing importance to architects and engineers. Unfortunately, buildings melting cars [cnn.com] is a thing that has happened, and urban heat islands are a c

      • Cooling the backs of solar panels works also. I've though about running water lines on the back of mine, but the cost relative to buying new panels, as low as 11c/watt, isn't worth it. Cheaper to buy more panels and screw the efficiency.
    • It's really innovative first generation tech. That's all.

      TFS estimates this will remove 93 watts per square meter.

      On average, the solar energy hitting the earth is 164 watts per sq. meter. An 8 hour summer day at 40 degree latitude can be as high as 600 Watts per sq. meter.

      There will still be some air conditioning needs in the places they are presently very popular.

    • It's a neat idea, but what happens in the winter? Seems like a good idea for the tropics, but otherwise not terribly useful.

      • Re: (Score:2)

        by skids ( 119237 )

        Yeah, winter homes will have to wait until they can make the film thermally sensitive so it only works in the summer. Or change windows seasonally. Maybe an installable storm window that reflects 10um back in. But really anything that is a chore is likely to not get done.

        (Currently there are different energy efficient glasses for northern versus southern U.S. homes, but it is harder to get the high-solar-gain/low-e type for north-facing windows in prefab windows for us northerners)

      • It's a neat idea, but what happens in the winter?

        Put a cover over it.

        Glass is good. It is pretty much opaque to far infrared. Instead of seeing the cosmic background temperature of a few degrees kelvin, it will see the temperature of the glass - which is about the same as its own temperature. So the radiative heat flow will be just about zero.

        But ANYTHING opaque to infrared will do the same.

        Another approach: Instead of coating the house, coat a radiative cooler to make chill water, and pump that through

    • University professors. Meaning they do it for science, and grant money, not to get filthy rich. The concept is out there but the next step is to make it feasible and affordable.

  • The heat is returned to the state in which it arrives, infrared radiation, and returned to space.

    Neither the building materials, nor the air in close proximity to it, get the chance to absorb the radiation and the heat the absorption develops.

    • The heat is returned to the state in which it arrives, infrared radiation, and returned to space.
      Neither the building materials, nor the air in close proximity to it, get the chance to absorb the radiation and the heat the absorption develops.

      A plain mirror could do that. The idea here is that infrared emitted by warm objects is absorbed and re-emitted at frequencies the atmosphere is transparent to, thus the heat escapes to space rather than warming the air.

      • Depends [edmundoptics.com] on what the mirror was made of. Some would absorb the heat activated by infrared "excitement" of their molecules.

  • Yeah, but WHEN? (Score:5, Funny)

    by JustAnotherOldGuy ( 4145623 ) on Sunday February 26, 2017 @12:55PM (#53933739) Journal

    Yeah, but WHEN? When will we see this available for consumer use?

    I see news stories every damn day about some amazing breakthrough in this field or that field, but fuck all if it ever seems to make it to market.

    I must have seen 100 stories in the last few years about more efficient and less expensive solar cells, but where the fuck are they?

    The same with medications and advances in medical technology....lots of news and hype and excitement but rarely does anything ever appear.

    FFS, all I want is to be buried in a casket made of an advanced polymer plastic film that eliminates diabetes and has a 98% solar conversion efficiency rate, and that can autonomously pilot itself down I-5 during rush hour. Is that too fucking much to ask?? Oh, and the battery has to last for a full week without a charge.

    • Re: (Score:3, Insightful)

      by Anonymous Coward

      All these 'advances' are a scam. Remember how computers were going to get more powerful, how we'd have literally megabytes of storage available? And they'd get smaller so we wouldn't have to lug around a briefcase+ size device like one day they'd be phone size? What happened to any of that? Don't get me started on the stories of how one day we'd be able to engineer genes directly. It's all pie in the sky. And like you say, medical research, all those stories about keyhole surgery and designer drugs. Never

      • Re: (Score:2)

        by lucm ( 889690 )

        Remember how computers were going to get more powerful, how we'd have literally megabytes of storage available?

        The problems scale faster than the solutions. For instance, I have a 32GB SD card on my phone, but guess what, that can only store 5 or 6 HD movies, and will probably be barely enough for the trailer of a 4k movie. By the time storage catches up, I will still only be able to store 5 or 6 movies in a 5-year old format and 0.1 movie in the newest format on a phone. Progress much.

        • Re: (Score:2)

          by tepples ( 727027 )

          But with how (physically) small a phone's screen is, what's the point of more than 480p or so if you're viewing it on a phone? Or are you using a full-size TV as the phone's monitor?

    • Pay attention. Solar cell prices have dropped dramatically over the last decade. Nobody has claimed the really efficient stuff (>40%) is cheap.

      Medical technology is reaching the public, despite the FDA's foot dragging. For example, the advances in available AIDS treatment has made a lot of news in recent years.

      • Nobody has claimed the really efficient stuff (>40%) is cheap.

        When your input energy is free, efficiency isn't a primary concern. Efficiency of solar panels only affects the overall size of the array for a given output power rating. Roof space is free, so who cares about efficiency, except for some niche applications?

      • Re: (Score:2)

        by amiga3D ( 567632 )

        The only thing keeping me on the grid is the price of batteries and the other associated electronics needed for a home system. The panels are the cheapest part of the system.

    • Re:Yeah, but WHEN? (Score:4, Insightful)

      by CanadianRealist ( 1258974 ) on Sunday February 26, 2017 @01:46PM (#53933957)

      I think maybe you're on the wrong website, you don't seem to be interested in new discoveries. You might be happier with a site which concentrates on something like "new products coming out this year."

      Many of us enjoy reading about new discoveries, knowing that not every promising new discovery will lead instantly to a mass marketed product. (If it ever does.) Every time there's a story about research on improving solar panels or battery efficiency there's always people complaining that they never see these things coming to market, ignoring the steady improvements that we see in both over time. For every story about improving ranges of electric vehicles there's someone who says it's useless because it doesn't meet their use case.

      If you really are an old guy think about all the progress you've seen in your lifetime. It didn't happen all at once, but we've sure come a long way. My first computer had 48 kb of ram, 5 1/4" floppies as the only storage, and I used a Model 33 Teletype as a printer. It was a home built Southwest 6800, for those old enough to know what that was.

      • Epic humor-impairment detected, resetting all expectation levels....done. Press any key to continue.

      • If you really are an old guy

        If?? I'll have you know that my original birth certificate came on a clay tablet.

        And we didn't have "computers", we had to throw rocks into baskets and calculate the outcomes through probability statistics. Not only that I had to walk 25 miles to school on my knees over broken glass every day, and it was uphill both ways! And this was before schools even existed! One time our dinosaur broke down and we all starved to death!

        I'm so old I don't even buy green bananas, and I only read Playboy for the articles!

        • Re: (Score:2)

          by amiga3D ( 567632 )

          We threw bones and had this guy with bones sticking through his nose and ears and lots of freaky tattoos and piercings that read them. Not much different from today now that I think about it.

    • Re: (Score:2)

      by DamonHD ( 794830 )

      This is a VERY boring trope. If you only want completely finished consumer grade tech then stop reading /. and go read a product catalogue, maybe on paper, and stop wasting our time on your public masturbation/trolling.

      For example, on another topic:

      https://slashdot.org/comments.... [slashdot.org]

      And yes those more efficient PV cells are emerging in several different directions depending on application, and I'm been installing some of them. In terms of W/$ (thus J/$) I've recently put up stuff that cost me 1/10th of what

      • I'm sorry that you, like some of the other responders, are so humor impaired. Perhaps a girlfriend or a hobby would be helpful, or maybe even moving to an above-ground location. :)

        • Re: (Score:2)

          by nasch ( 598556 )

          I'm sorry that you, like some of the other responders, are so humor impaired.

          It's very difficult to tell the difference on the internet between a joke and something an idiot says. It's almost impossible if the joke isn't funny (which yours wasn't). When you write a joke, take another look at it and think "is there any possible way a human might say this to either be serious or troll other people?" If so, then it probably isn't going to land as a joke.

      • I got an advertisement in the mail this week for solar panels at 11c/watt. They're grade C, but I'm sure most would last the 6 month it will take to break even.
  • I would be more interested in this if it worked the other way, warming my house. Where I live, I need the furnace to run 9 months of the year. And 5 of those 9 months every day. Last year, I ran my AC on 8 days.
    • You can put an IR film on your windows to trap heat inside. You can use a heat pump to take heat from the ground and dump it in your house (most cheap units take from the cold air, but the ground has more heat).

    • I would be more interested in this if it worked the other way, warming my house.

      There are lots of designs for doing that. Look at any renewable energy bulletin board (such as fieldlines.com).

      Common thread is:
      - Black (or otherwise visible light absorbing) target.
      - In an insulated box.
      - With a glass window (that does NOT have an infrared reflective coating)
      - And some way of transferring the heat from the black target to the house air.

      Glass is opaque to infrared and passes visi

  • Maxwell's Demon? (Score:4, Interesting)

    by Gim Tom ( 716904 ) on Sunday February 26, 2017 @03:49PM (#53934491)
    This sounds almost like Maxwell's Demon -- which makes me very skeptical.

  • I've seen a lot of films and paints the last couple of years using some form of reflectivity to lessen heat absorption. All fine and well until they get a fine layer of dust after a couple of weeks. Then they are useless.

    I'm not to well versed in the physics of this (meaning not at all), so I wonder how this invention will hold up under real world dusty conditions.

  • Ok, so what happens if you put this on something really HOT like a car engine running at 500C or maybe a jet engine at 1000C or a rocket engine at 2000C? (Of course, you'd replace the plastic "film" with something else or perhaps just apply the nano-beads directly.)

    Would they REALLY benefit from the "huge temperature difference ... to outer space", so much so that they didn't require complex cooling systems but could instead just radiate their heat directly? (I presume that this would mean the hot parts w

    • If you can make the nano-beads just a bit smaller, you could do the same tricks but with VISIBLE LIGHT. Think paints that would really glow at specific frequencies. Shine a blue light on it and it would glow red! Even if expensive, it could be used for specialized inks (think anti-counterfeiting).

      That would be a Dichroic filter [wikipedia.org], that's what's in the reflector in your Dentist's light. It's adjusted to only reflect light frequencies that mimic a 4,500K blackbody.

  • Put this on an insulated box, which then gets colder than its surroundings. Use the box interior as the heat sink for a heat engine with a heat source exterior to the box.

    Sounds like boolsheet.

  • It's demons I tell you. DEMONS!!!!
  • Since we have many uses for heat maybe w could capture the heat exhausted from that system as well as use it for cooling. And we just might be able to collect water from that cooled air as well.

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