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posted by cmn32480 on Sunday August 28 2016, @05:06PM   Printer-friendly
from the can-they-stop-me-from-seeing-the-neighbor-in-his-speedo? dept.

Arthur T Knackerbracket has found the following story:

By fine-tuning the chemical composition of nanoparticles, A*STAR researchers have developed a coating that is promising for fabricating smart windows suitable for tropical countries. Such windows block almost all the infrared heat from sun rays, while admitting most of the visible light.

The transparency of glass to visible light makes it the most common way to let light into a building. But because glass is also transparent to near-infrared radiation—windows also let in heat, giving rise to the well-known greenhouse effect. While this heating is welcomed in colder climates, it means that air conditioning has to work harder to maintain a comfortable temperature in in tropical climes.

Developing smart windows that allow most of the sun's light in, while blocking near-infrared radiation, would cut energy costs and reduce carbon emissions.

"In tropical Singapore, where air conditioning is the largest component of a building's energy requirements, even a small reduction in heat intake can translate into significant savings," notes Hui Huang of the A*STAR Singapore Institute of Manufacturing and Technology.

Huang and his co-workers have developed such windows by coating glass with tin oxide nanoparticles doped with small amounts of the element antimony. By varying the nanoparticles' antimony concentration, they could optimize their ability to absorb near-infrared radiation.

"Our infrared shielding coating, with 10-nanometer antimony-doped tin oxide nanoparticles, blocks more than 90 per cent of near-infrared radiation, while transmitting more than 80 per cent of visible light," says Huang. "These figures are much better than those of coatings obtained using commercial antimony-doped tin oxide nanopowders. In particular, the infrared shielding performance of our small antimony-doped tin oxide nanocrystals is twice that of larger commercial antimony-doped tin oxide powders."


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  • (Score: 3, Interesting) by TheLink on Sunday August 28 2016, @05:34PM

    by TheLink (332) on Sunday August 28 2016, @05:34PM (#394267) Journal

    How much better is it compared to existing tech? Existing tech already seems to do similar stuff: http://www.3m.com/3M/en_US/company-us/all-3m-products/~/3M-Sun-Control-Window-Films-Prestige-Series-for-Commercial?N=5002385+8709317+8710037+8710654+8710938+8711017+8721693+8730565+3292716662&rt=rud [3m.com]
    (reject 97% infrared, let in 70% visible). From the article, this "new" tech "blocks more than 90 per cent of near-infrared radiation, while transmitting more than 80 per cent of visible light,". So is the difference that it blocks 90% near-infrared while existing can only block 97% infrared and lets a lot more near-infrared through?

    Anyway I'm more interested in stuff like this and whether it has progressed much since:
    http://www.sciencemag.org/news/2014/11/new-way-cool [sciencemag.org]
    http://www.nature.com/nature/journal/v515/n7528/full/nature13883.html [nature.com]
    https://www.technologyreview.com/s/532826/material-cools-buildings-by-sending-heat-into-space/ [technologyreview.com]

    researchers in California have created a new multilayer coating that cools using a one-two punch. First, it reflects nearly all the incoming energy in sunlight. Second, it absorbs heat (say, from a building below) and radiates it away without warming the nearby air.

    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.

    Basically if you put this stuff in bright sunlight it still ends up 5 degrees Celsius _cooler_ than ambient air temp! 5 Celsius is a big difference.

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  • (Score: 2) by JoeMerchant on Monday August 29 2016, @12:50PM

    by JoeMerchant (3937) on Monday August 29 2016, @12:50PM (#394631)

    Solar film has been "a thing" since the 1970s, and they had quite good films by the 1990s - perhaps already as good as the 90% IR block with >60% visible pass. I bought some "lowE" glass and installed it in my home a few years ago, not a film but a coating on the glass... one challenge is that the films and coatings aren't as durable as the glass itself - I'm looking at an indelible handprint in some 1970s film on my bedroom window now.

    Maybe this is "news" because "nanoparticles"? Maybe it is cheaper to make than the lowE stuff on the market. More likely it's some academics who just discovered a way to accomplish the same things that have been in commercial production since before they were born... maybe their way can be developed into a superior commercial process, but likely not without significant development/investment, which, if applied to existing tech, might yield similar improvements.

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  • (Score: 2) by JoeMerchant on Monday August 29 2016, @01:00PM

    by JoeMerchant (3937) on Monday August 29 2016, @01:00PM (#394638)

    That cooling coating is "super cool" (not really, but...)

    I'd be interested in cost per sqft, as well as durability. But... the idea that it re-radiates heat that can escape to space is awesome, most air conditioners just dump your indoor heat, plus some extra, into the air just outside. Now - does that radiated heat actually make it out into space, or is it reflected by greenhouse gases? Either way, it's much farther away than your AC condenser fan.

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    • (Score: 2) by TheLink on Monday August 29 2016, @03:45PM

      by TheLink (332) on Monday August 29 2016, @03:45PM (#394769) Journal

      There's a limit of how many watts it can radiate per area. Currently the _net_ difference seems to be about 40W per square metre to get it to ambient temperatures:
      http://web.stanford.edu/group/fan/publication/Raman_Nature_515_540_2014.pdf [stanford.edu]
      e.g. 800W of sunlight hits the 1 square metre of the material but you can still pump in 40W to the material to heat it to ambient. So if the material only reflects 700W and absorbs 100W then it's radiating about 140W away (ignoring convection etc coz I'm lazy).

      I wonder if it's worth using it to make ice at night. Or the efficiencies drop too much? https://en.wikipedia.org/wiki/Radiative_cooling#Nocturnal_ice_making [wikipedia.org]

      Having something cooler in the shade is normal. This is close to magic - imagine showing people in the past (or many even today) an object that stays cool the whole day in full daylight: http://www.nature.com/nature/journal/v515/n7528/fig_tab/nature13883_F3.html [nature.com]

      • (Score: 2) by JoeMerchant on Monday August 29 2016, @11:42PM

        by JoeMerchant (3937) on Monday August 29 2016, @11:42PM (#395004)

        If you haven't watched "The Mosquito Coast", you should.

        I've looked at lots of "ice at night" schemes, hoping to find something that could become an off-grid cooling scheme - but, in the end analysis, they're all incredibly weak as compared to a gallon of gasoline, a generator, and a 5000 BTU/hr window A/C unit. I really hate the noise aspect of generators, and A/C units both - but a BTU raises a pound of water one degree F - the water-ice transition is ~144 BTUs/pound - so, a scrawny window unit A/C can take 26 pounds of water from 80F to ice per hour. If you want to cool a room like a 5000 BTU/hr AC can, you're going to need on the order of 30 pounds of ice per hour, or about 240 pounds of ice, just for 8 hours of cool sleeping time - 720 pounds of ice per day. Now, if you had a 100 gallon ice maker that could make 800 pounds of ice a night, then you could bank that ice and use it to cool a well insulated bedroom. Most of the "solar ice maker" plans I have found on the internet have over 40 square feet of cumbersome circular reflectors and they claim to make about 10 lbs of ice "on a good day." Scale that up, you'll need 320 square feet of reflectors on the roof to make the ice to cool about 200 square feet of living space... If I had nothing but time on my hands and money to burn, I'd build it just to see it work, but it would be quite aesthetically challenging, not to mention the chore of reflector cleaning.

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