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New Spray-On Coating Can Make Buildings, Cars, and Even Spaceships Cooler (bgr.com)

Posted by EditorDavid on from the you-look-radiant dept.

Long-time Slashdot reader davidwr and Iwastheone both submitted this story about "a paint-like coating that facilitates what is known as 'passive daytime radiative cooling,' or PDRC for short...when a surface can efficiently radiate heat and reflect sunlight to a degree that it cools itself even if it's sitting in direct sunlight." BGR reports on research from the Columbia School of Engineering: Their newly-invented coating has "nano-to-microscale air voids that acts as a spontaneous air cooler," which is a very technical and fancy way of saying that the coating is great at keeping itself cool all on its own. "The air voids in the porous polymer scatter and reflect sunlight, due to the difference in the refractive index between the air voids and the surrounding polymer," Columbia writes in a post. "The polymer turns white and thus avoids solar heating, while its intrinsic emittance causes it to efficiently lose heat to the sky."

It sounds great, but the best news is that it can be applied to just about anything, from cars to spaceships and even entire buildings. The team believes their invention would be an invaluable resource for developing countries in sweltering climates where air conditioning is impractical or unavailable.

43 of 86 comments (clear)

  1. Does it work on people? by MrKaos · · Score: 4, Funny

    For example if someone is being a bit of a dick, you just spray some of this on them and they become cooler?

    You'd be the life of the party.

    --
    My ism, it's full of beliefs.
    1. Re:Does it work on people? by sysrammer · · Score: 1

      Ha! That headline was just begging for a comment like yours. I know some people who'd have to be dipped in it.

      --
      His ignorance covered the whole earth like a blanket, and there was hardly a hole in it anywhere. - Mark Twain
    2. Re:Does it work on people? by MrKaos · · Score: 1

      It's called pepper spray.

      lols!

      --
      My ism, it's full of beliefs.
  2. It's called "white paint" by PeeAitchPee · · Score: 1

    Seriously, how much better is this than using plain old white paint?

    1. Re:It's called "white paint" by drinkypoo · · Score: 4, Informative

      Seriously, how much better is this than using plain old white paint?

      It's better in that a white surface doesn't radiate much, so even though it reflects most of the energy that strikes it, it still heats up. It's worse in every other way. These nanoscale structures are always fragile and turn into nanoscale dust, and which don't break down easily (because of what they're made of) which makes them persist in the environment. Auto paint is expected to last for decades in harsh conditions, but they gave that as an example anyway.

      --
      "You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
    2. Re:It's called "white paint" by Iwastheone · · Score: 2, Interesting

      I've done a lot of roofing in my life, one type being a rubber roll that gets melted down with a propane torch for flat roofs. An aluminum coating in a can needs to be applied to the rubber roof in order to reflect the ultra-violet rays of the Sun. If this special coating isn't applied, the rubber rots away within 5 years. Reapplying this silver coating every 5 years can almost indefinitely extend the life of the rubber roof. Does this material do this also?

    3. Re:It's called "white paint" by hankwang · · Score: 2

      In thermal properties it's not different from most other white materials or white paint: they absorb and emit well in the thermal infrared range (5 to 15 micrometers) and reflect well in the visible and near-IR (400 nm to 1500 nm). Even plain white paper would do the job. The effect of this fancy coating is possibly a marginal improvement in the 1500-2500 nm range, but sunlight does not carry that much energy in that range.

      The opposite is much harder: absorb sunlight but don't emit or absorb thermal infrared. That's what you need for solar water heating. It can be done (silicon layers on top of reflective metal) but it is expensive and sensitive to contamination.

      --
      Avantslash: low-bandwidth mobile slashdot.
    4. Re:It's called "white paint" by mspohr · · Score: 2, Insightful

      Seriously, if you read TFA, you'll find out that:
      1. It's more reflective than plain white paint
      2. It emits IR which can actually bring the surface temperature BELOW ambient.

      --
      I don't read your sig. Why are you reading mine?
    5. Re: It's called "white paint" by goombah99 · · Score: 1

      How does it get below ambient? Can I power a steaming engine with that?

      --
      Some drink at the fountain of knowledge. Others just gargle.
    6. Re:It's called "white paint" by Iwastheone · · Score: 1

      A video of said coating ( https://www.youtube.com/watch?... )

    7. Re: It's called "white paint" by mspohr · · Score: 1

      Maybe.
      It emits IR

      --
      I don't read your sig. Why are you reading mine?
    8. Re: It's called "white paint" by popoutman · · Score: 1
      Things dropping below ambient air temperature is extremely common. The simplest examples would include nighttime ground surfaces when the sky is clear. There's a reason why the edges of fields and the areas near walls and trees is the last to get frosted up

      In essence, the temperature of an object depends on the heat transfer between itself and its surroundings. This transfer can be of conduction, convection, or radiation. For objects that are not fluids, that is limited to conduction and radiation. Now, air is a pretty good insulator and a poor fluid for the transfer of heat. Noting that the effective temperature of a clear sky at night is in the negative 40 degrees or lower, it then becomes fairly easy to see that the object in question will radiate a lot heat in that direction without a balancing flow of heat back. If that object were in an enclosed room, then the room surfaces would be transferring heat to the object at the same rate the object would be transferring heat to the surfaces - no change in temperature. There is heat transfer between the air and the object by conduction, but that is a very inefficient process by comparison especially when the air is still - and heavy frosts happen more easily with still air.

      Telescopes can regularly reach a few degrees below ambient and then become cold enough for dew to condense on the optics and the tube structures, because the optics can be exposed to the cold sky and the optics are not being warmed effectively by the surrounding air.

      Whether one can power a steaming engine with that, well if you have a working fluid in the right temperature range of course you can. The available power though would be very small given the delta-T present. It may be possible to measure a voltage with a very large Peltier setup sinking heat by radiative cooling only, but not enough current to be practical and especially for the cost of setup..

      Theoretically this would be a version of Solar, where daytime heating and night time cooling is the driving force.

      --
      - This sig deliberately left blank. Nothing to see, move along.
  3. Useful in the Developed World by mykepredko · · Score: 1

    I would think that this coating would be useful in the developed world where a coating like this would reduce air conditioning requirements for homes and buildings.

    The biggest issue would be that the buildings/cars would become a lot more whiter and I suspect more blinding in direct sunlight.

    --
    Mimetics Inc. Twitter
    1. Re:Useful in the Developed World by Mr+D+from+63 · · Score: 2

      Questions that come to mind are "how much emittance occurs which there is a high delta-T? How long does the coating last and how easily is it's emittance reduced by normal environmental conditions (dirt, microbials, etc)? How much would it cost? Any toxicity concerns?

    2. Re:Useful in the Developed World by DCFusor · · Score: 1

      Also, for we who live in a 4 season climate - how to turn it off in winter. We expend energy to both heat and cool.

      --
      Why guess when you can know? Measure!
    3. Re:Useful in the Developed World by hawk · · Score: 1

      This.

      Replacing original windows (which were *all* tenant damaged anyway) with doublepane and non-metal frames made a *huge* difference in the desert summer . . . and when winter rolled around, my ife started claling them "you stupid windows" because the house didn't warm as fast in the morning . . . ..if it were trying to radiate away heat, it would have taken evne longer . . .

      hawk

    4. Re:Useful in the Developed World by drinkypoo · · Score: 1

      and when winter rolled around, my ife started claling them "you stupid windows" because the house didn't warm as fast in the morning

      There are two separate considerations when selecting windows, R-rating and E-rating. Multiple panes raise the R-rating. Coatings lower the E-rating. The E-rating measures how much non-visible light passes through the glass. Passive solar designs use glass with a high R-rating and a low E-rating, meaning that they don't let as much heat energy escape by conduction, but they let solar energy enter via radiation. And they use overhangs or awnings to prevent that from happening in the season when the sun is overhead, but which permit it to come in during the cold season.

      --
      "You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
    5. Re:Useful in the Developed World by DCFusor · · Score: 1

      Yup, we need things like that to be reversible. It really matters here as I'm off-grid so heating and cooling have to mostly be non-electric. An amount of solar that lets my keep my Volt charged up (mostly) won't do the HVAC kinda stuff...that's wood, propane, and mostly small fans, only a little AC. And it does get hot here, but also spends time around 10F. Lots of degree-days.

      --
      Why guess when you can know? Measure!
    6. Re:Useful in the Developed World by White+Yeti · · Score: 1

      Agreed. Unless it works under a clear-coat, the normal progression of house paint along the Gulf coast is white--> green--> brown--> powerwash--> beige -->repeat from green.

    7. Re:Useful in the Developed World by thoughtlover · · Score: 1

      Sounds like a crude, reverse-engineered Starlite.. White paint's got nothing on this seemingly revolutionary product... what a history of what never became.

      Note: I just became aware of this chemical marvel via a recent /. post remembering its history. Here's the BBC video that's referenced in the synopsis.

      https://www.bbc.com/reel/video...

      --
      No sig for you! Come back one year!
  4. or use better building materials by js290 · · Score: 1

    Compressed Earth Blocks: Why and How, Here and There https://youtu.be/IuQB3x4ZNeA

    --
    "Tempers are wearing thin. Let's just hope some robot doesn't kill everybody." --Bender
    1. Re:or use better building materials by Aighearach · · Score: 1

      The part you missed about the story of the three little piggies; their economy wouldn't support a brick house for all three. It isn't a story about smarts, it is a story about the difference in outcomes according to resource access.

      The thing about "compressed earth blocks" is, they're not bricks. As you noticed when talking about clay. Instead, they're something that can be made from a much wider range of input materials. That means that production can be scaled without boosting the price by competing for raw materials with all the other construction technologies. Clay is sometimes locally plentiful, but not compared to dirt. And the main other input is electricity, so you could have a giant factory in an arid region with lots of solar generation, and just run the machine during peak daylight.

      You could build a factory in a poor country, and the people could actually use them to build houses. If you build a factory making clay bricks, those have more export value and somebody will get rich, and the villagers will still only have grass huts, or scrap and tarps, as the case may be.

    2. Re:or use better building materials by drinkypoo · · Score: 1

      Earth bags can use an even wider range of soils, and use minimal materials. They do require that you come up with some burlap, and ideally barbed wire as well (to run between the courses) but they don't require compaction, just bag-filling.

      --
      "You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
  5. alrighty by AndyKron · · Score: 1

    Between this an solar freakin' roadways the world should just about be saved.

  6. Any concerns about nanoscale particles? by Aristos+Mazer · · Score: 2

    How well does this paint clump together? As a spray, it seems likely that some of the particles would linger in the air. Medical researchers are still trying to get a handle on the risks of nanoparticles to living beings -- we just aren't made to filter stuff at that level because its not common in the natural environment for there to be free-floating bits at the nanoscale. It might be safe, but we don't currently know. Here is one report from the UK government just listing the research unknowns about nanoparticle exposure. Before we start spraying whole buildings in stuff like this, we should know the environmental and health impacts. I hope the inventors of this stuff start working on those questions before they try to productize this.

    1. Re:Any concerns about nanoscale particles? by jimbolauski · · Score: 1

      Spraying it on buildings would be out of the question until those questions can be answered, inside paint booths where air is run through filters and respirators are required would be the only place it could be used.

      --
      Knowledge = Power
      P= W/t
      t=Money
      Money = Work/Knowledge so the less you know the more you make
  7. reciprocity, emissivity reflectance by goombah99 · · Score: 2

    This is a tricky point of physics which is seldom explained well, and I don't understand it much more than the basic idea. But in nearly everything emissivity at a given wavelength is the compliment (1-x) of the reflectance.

    It's a frustrating idea because it says that while white can keep the sun off you (reflecting) it also doesn't radiate either keeping you hot.

    Now the escape clause here is that if you are not as hot as the sun, then your black body emission is in the mid IR while the sun is peaked in the visible. Thus if you can make something white looking in the visible but black in the Mid IR it can beat the system and help cool by both reflection of the sun and thermal emission.

    Now this device seems to be arguing for something different it sounds like they are saying they use a dark (emissive) material but then make it so granular and scattering that it looks white (which indeed is why clear crystals look white when you powderize them (e.g. sugar).

    But my understanding of this, possibly wrong which is why I'm asking, is that it doesn't matter why something looks white to the emissivity/reflectance relation. If a nominally black material "looks" white to the eye then it's going to act identically to an object that is actually pigmented white. It doesn't matter if its refraction, reflection of pigment that causes it to be white. White is white.

    THus the explanation seems like B.S. However it still might be working just fine for the old boting reason of being a mid IR black object. that just would not be news.

    The reason I'm wobbly on this is when you think about absorbption down at the atomic transition scale then the whole emissivity, reflectance thing gets confusing. It becomes unclear how discrete spectral lines actually add up to that. It's much easier to treat the relation at the macroscopic black body level.

    SO is it really possible for this nano scale voodoo to do something other than white paint does?

    --
    Some drink at the fountain of knowledge. Others just gargle.
    1. Re:reciprocity, emissivity reflectance by Ramze · · Score: 4, Informative

      I've been reading about this daytime cooling through infra-red emissivity to space stuff for a while now. The biggest benefit isn't the color (or the reflective value), but that it will absorb heat from whatever the source and radiate that energy away in the mid-IR band that will allow it to leave Earth's atmosphere without being re-absorbed by anything nearby. That makes it effectively a way to remove heat from the surface of the earth by emitting that energy into space.... heat that would otherwise be trapped by our atmosphere's greenhouse effect.

      This is the first time I've seen this expressed as a coating for everyday consumer items rather than as a heat sink layer added to an exterior A/C unit or a potential roofing material, though.

      My understanding is that generally these coatings are white in the visible spectrum to reflect sunlight, but emit light in the mid-IR range. There's a startup company for using this to improve efficiency in A/C units I read a while back, and they tested the material in the hot sun on a roof in India -- you could put your hand on it after it had been baking in the sun, and it was cool to the touch. That's relative term, though. I don't recall the actual temperature readings.

  8. I Need this Yesterday by RT+Cunningham · · Score: 1

    The air conditioner in the master bedroom of my house in the Philippines runs constantly from mid-March to Mid-June. It's their version of summer. The sun heats up one side of the house and that's all it takes. I need this product there as soon as I can get it. Somehow, I think it will be years from now.

    1. Re:I Need this Yesterday by onepoint · · Score: 1

      While I can not give you a solution to your problem with paint, I do have a fun solution which is working with sunlight heat reduction. I use a thin cheesecloth over my plants in my garden with. it's slightly cooler by 4C to 7C. I've tried it for myself and it's very nice to read in this type of shade. just an idea, that's all nothing tech about his.

      --
      if you see me, smile and say hello.
    2. Re:I Need this Yesterday by Pinky's+Brain · · Score: 2

      They only claim to do it better, they are not the first. Skycool in Australia has been selling their wavelength selective reflecting/absorbing paint for over a decade now. Unfortunately they don't seem to want to get into the consumer or even small contractor supply chain, or at least they don't hint at it on their latest website. On their old website they had a link to a contractor, but that one is dead now.

      https://www.skycool.com.au/

    3. Re:I Need this Yesterday by RT+Cunningham · · Score: 1

      I understand the concept but it wouldn't work in this instance. It would have to be huge (if I could even find it there).

    4. Re:I Need this Yesterday by RT+Cunningham · · Score: 1

      I'm already using a very light-colored paint. Putting something in between the wall and the sunlight is probably the only option I have.

    5. Re:I Need this Yesterday by onepoint · · Score: 1

      https://www.amazon.com/Tobacco...

      this is the concept you need, 180ft x 36 inch,
      find it at Divisoria Market in Manila

      hope you get lucky

      --
      if you see me, smile and say hello.
  9. HOAs! by TechyImmigrant · · Score: 2

    I'd love to see what crap the HOA comes up with when I paint my house white.

    --
    I should use this sig to advertise my book ISBN-13 : 978-1501515132.
    1. Re:HOAs! by TechyImmigrant · · Score: 1

      I have. I'm on the board (to keep a crazy rule nazi off the board).

      We're good with solar panels. That's a fed thing as are the antenna rules.
      We're good with painting the roof - They're flat and not visible from the street
      Painting the front - there's no local ordinance for that.

      --
      I should use this sig to advertise my book ISBN-13 : 978-1501515132.
  10. Re:Slashvertisement - retarded fake news by Cederic · · Score: 1

    Tell me more about the vacuum of space, and how it prevents heat radiation.

    Include, if you could, how your explanation applies to that small yellow thing in the sky that blinds me when I look at it.

  11. Back inthe '70's or so... by beep54 · · Score: 1

    they tried cooling tall buildings by making them semi-reflective. Obviously, this was not thought thru well. I remember one skyscraper near I35 (which was practically already a death trap) that would blind you at certain times while driving. Like rush hour. Gawd only knows what it cost to fix these buildings.

  12. And... by Pravetz-82 · · Score: 1

    ... it is carcinogenic.

  13. Re:Slashvertisement - retarded fake news by drinkypoo · · Score: 1

    Actually, that's probably the best use of this kind of coating that I've seen mentioned in this discussion. It would mean not having to shield your radiators from sunlight. This is a good argument for white spaceships.

    --
    "You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
  14. Keyword: POLYMER by macraig · · Score: 1

    What the inventors don't want you to think about is that this is essentially a consumable product. Polymers de-polymerize and lose their beneficial properties over time, especially when exposed to solar radiation... which is the intended point of this stuff. It will have to be replaced repeatedly as it fails.

    This solution to the problem is akin to Big Pharma's tactics: rather than develop one-time permanent solutions, they concoct band-aids that require a lifetime subscription to get any benefit.

  15. Can we quickly paint our president ? by Archfeld · · Score: 1

    Trumplestiltskin needs all the help he can get. Come to think of it I was told by my GF's 14 year old that while I wasn't terminal, like her mother, just because I could board or inline skate did not make me cool anymore :(

    --
    errr....umm...*whooosh* *whoosh* Is this thing on ?
  16. Make ME cooler by jtgd · · Score: 1

    Is there any way this technology could be integrated into clothing?

    --
    J