
A film that can cool buildings without the use of refrigerants - feelthepain
http://www.economist.com/news/science-and-technology/21716599-film-worth-watching-how-keep-cool-without-costing-earth
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voltagex_
[http://science.sciencemag.org/content/early/2017/02/08/scien...](http://science.sciencemag.org/content/early/2017/02/08/science.aai7899)
is the paper linked in the article

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Retric
Did not read the article, but the abstract is misleading.

It does not matter if the atmosphere absorbs the radiation from your device or
it reaches space, after a few feet it's irrelevant. The important bit is the
underside of the tarp which is not going to be below ambient temperature.
Making the absolute best it can do the equiviemnt of a fan on the roof which
can't replace AC.

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caf
It absolutely _does_ matter, because the beads that are tuned to radiate
particular frequencies of infrared will also be tuned to _absorb_ those
frequencies as well. If the frequencies aren't transparent to the atmosphere,
you'll be reabsorbing just as much as you transmit and end up at equilibrium
with the atmosphere.

It is essentially similar to the way in which you can freeze water in a
shallow dish on clear nights that are nonetheless slightly above freezing
temperature - you are facing a black-body radiator that is well below ambient
local temperature.

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Retric
At night sure, in the day time the sun is adding heat across a wide band of
frequencies. This heats up less, but does not drop below ambient temperature
in full sunlight.

PS: You don't actually need a thing special at night to get this effect:
[http://www.asterism.org/tutorials/tut37%20Radiative%20Coolin...](http://www.asterism.org/tutorials/tut37%20Radiative%20Cooling.pdf)

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averagewall
The advantage of targeting the IR window is that it would work even with
clouds and water vapor in the atmosphere whereas, plain old thermal radiation
needs a clear night to be effective.

Of course it won't pump heat backwards into the sun but they propose a water
circulation system, which I imagine could store some daytime heat to release
it at night. That and masonry of the walls of the building would store even
more.

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lovemenot
How lovely that the two inventors are Doctors Yin and Yang.

Presumably Dr. Yin was responsible for energy absorption and Dr Yang for
energy emission.

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clort
I saw this and smirked internally of course, but noticed in the article itself
they did refrain from trivialising the names of the inventors in this way, by
referring them to Dr Yang and Dr Yin throughout.

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asafira
I fell in love with this idea when it first came out! Here is the first
demonstration of it a couple of years ago:
[http://www.nature.com/nature/journal/v515/n7528/abs/nature13...](http://www.nature.com/nature/journal/v515/n7528/abs/nature13883.html)

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stuaxo
This would be great in hot countries, where so much energy is used in air
condition, it could make a real dent in energy use, and hence pollution.

~~~
sfifs
Most homes in hot countries are not cooled with air conditioning because most
people in hot countries are too poor to afford it. Even the rich 1% tend to
use air conditioning only on a room by room basis, almost never the whole
house.

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ro_sharp
As an Australian in the depth of a hot summer, I beg to differ!

Almost every new house here includes a big air conditioner, and during hot
months the euphemistically named 'load shedding' is often performed:
[http://www.afr.com/news/politics/sa-power-crisis-may-
spread-...](http://www.afr.com/news/politics/sa-power-crisis-may-spread-to-
nsw-as-heatwave-hits-20170209-gu99ez)

Thus any improvements to (more) passive cooling technologies are very welcome

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gambiting
I wouldn't describe Australia as poor though.

Where I'm from(Poland) summers can get stupidly hot, 40C on some days, it's
difficult to sleep at night, yet I don't know anyone who has air conditioning
at their house. It's a huge luxury, due to the cost of the unit + cost of
electricity to run it.

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ChuckMcM
Wow, that is an awesome result. With a cooling panels on the shade side of the
roof and water pipes behind your PV panels on the sun side you can boost solar
PV production by 3 - 5%. PV panels become less efficient when they are hot, we
put some drip irrigation drippers on roof behind our panels (the panels are
about 4" above the roof surface) and the evaporating water improved production
by 2% on otherwise hot days.

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manmal
Do you mean 2% or 2 percent points?

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ChuckMcM
2%, in my case generating nearly an additional kilowatt hour per 24 hour
period (33.8kwH vs 33.2kwH).

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mrfusion
Also it would make a great clothing to wear in the summer or on a spacecraft
heat shield.

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averagewall
It wouldn't be useful on a spacecraft because it takes advantage of a
transparent band in the Earth's atmosphere. In space, you have that already at
all wavelengths.

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cgriswald
More to the point, a heat shield is used for re-entry and this stuff would
decompose almost instantaneously. It's be like trying to use a handheld fan to
cool yourself while standing in a kiln.

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WallWextra
How long can this stuff last on your roof? Will it shed glass microbeads
everywhere when the UV degrades it?

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Baeocystin
Probably. A cursory google search shows that TPX is prone to thermal
degradation. But glass microbeads do not have the same negative environmental
impact as plastic ones. They are already naturally omnipresent in the
biosphere.

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vanderZwan
Wouldn't the latter effectively be equivalent to sand?

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Baeocystin
Essentially, yes.

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jsilence
Does light in other wavelengths pass through with little transmission losses?
Then it might be an elegant way to cool green houses in the summer. Yes, they
can simply be vented, but it makes sense to keep them closed in order to keep
CO2 fertilization inside and bugs outside.

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ph0rque
My favorite method for cooling (and heating) greenhouses is ground to air heat
transfer (GAHT): [http://www.ceresgs.com/climate-
control/gaht/](http://www.ceresgs.com/climate-control/gaht/)

Note: this is similar to, but not the same, as geothermal heating.

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jsilence
Yes! I would love to have a research greenhouse fitted with this tech. Thumbs
up!

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jrockway
I have fifty cents. Where can I buy a square meter of this from?

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_rpd
It was only just described in a Science paper, so you are probably going to
have to wait 10 years before you can buy it at your local hardware store.

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waqf
So, in what sense is it true that it _costs_ (present tense) 50¢/m²?

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amalcon
It's a manufacturing cost estimate, not a market price.

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yellowapple
It seems reassuring that there's already a manufacturing cost estimate and
that it's as low as 50¢/m².

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pbhjpbhj
Patents will ensure it sells for $100 per square-meter though, or whatever
ludicrous price can be burn by the market and still make it valuable to the
consumer.

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CamperBob2
I'm not sure I get how the beads re-radiate energy at 8 microns that came in
at other frequencies. If the energy _didn 't_ come in at a different
frequency, then the building isn't going to end up any cooler. If it did, then
the beads are essentially phosphorescing in the IR region, aren't they? Or
exhibiting some other form of nonlinear conversion?

That would be pretty cool, no pun intended.

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Gibbon1
I would believe that the heat energy gets transferred to the beads by
conduction and or radiation.

I tend to think this is like a gas mantle in a gasoline (propane) lantern. The
mantle is doped with rare earth that emit more strongly in the visible section
than a black body would. On this case the temperature is much lower of course
and the glass beads are sized to emit strongly in an the infrared band that
isn't absorbed by the atmosphere.

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caf
A "reverse pool blanket" made of this material would be great for places where
swimming pools get unusably hot in summer.

~~~
sfifs
are there such places on earth where people live? I live in India and haven't
come across such :-)

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caf
Far North Queensland is one I've been to.

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andrewwhartion
Swimming in a concrete/Pebble Tec pool in Cairns in the summer is akin to
taking a warm bath...

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gewa
How is this not violating the second law of thermodynamics ? It seems like the
entropy as a whole is getting lower.

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milcron
Did you read the article?

    
    
        The new film works by a process called radiative cooling. This takes
        advantage of that fact that Earth’s atmosphere allows certain wavelengths
        of heat-carrying infrared radiation to escape into space unimpeded. Convert
        unwanted heat into infrared of the correct wavelength, then, and you can
        dump it into the cosmos with no come back.
    
        the work is done by the huge temperature difference, about 290°C, between
        the surface of the Earth and that of outer space.

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a_t48
Could we cover large portions of the Earth with this material and reverse
global warming?

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monochromatic
Probably wouldn't be cost-effective, but it'd work in principle.

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sqeaky
Seems innovative and awesome if true, but it is not so awesome as to be
without issues. Clearly this is great for places that are always warm, slap
this stuff on every building in Texas.

But what about places with erratic weather, or even just seasonal changes? It
seems like this will need to be some way to flip this stuff.

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wccrawford
The article says that the material is only half the solution. The other half
is pipes with water to move the heat to the material so it can be dissipated.
I assume that if you stop moving as much water, it doesn't cool as much. (It
can't radiant heat that isn't there.)

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woodandsteel
This is really cool (pun intended).

I wonder if you could integrate it with a solar cell, so you would get both
cooling and electricity.

It would be nice if they could figure out how to turn the effect off at the
film, instead of having to pipe water.

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ph0rque
Have another film above it that can be switched from reflective to
transparent? These already exist, but are made of exotic materials (vanadium
oxide, if I recall correctly) and thus expensive.

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ChrisFoster
Wow, this is such a beautiful example of basic science turning into powerful
technology. Technology which looks like it will be both cheaper and better for
the environment than any current alternative.

Does anyone have an idea of how long this might take to get to market as a
rooftop heat exchanger for domestic use? I guess it largely depends on
durability of the film; presumably the heat exchanger part of the system is a
known quantity.

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dxhdr
"50 micron thick polymethylpentene mixed with tiny glass beads"

As an achievement in science this is cool, but... we should be reducing energy
consumption while also not polluting the surface of the planet. Where's this
stuff going to end up when houses covered with it are torn down in 30-100
years?

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asafira
To be clear, this is actually a very small amount of plastic. Let's say a roof
is 300 square meters; that amounts to < 2 cubic centimeters of plastic.

I would guess that there are examples of much larger consumers of plastic.

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DiabloD3
That'd make it far less plastic than is currently used for roofs just for the
vapor barrier under roofing tiles.

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jbmorgado
Well, at first sight this seemed really nice.

But then, after thinking a bit about it (in my semi frozen office because
someone turned out the heating during the night), won't this increase the
heating costs a lot during the winter?

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ainiriand
How is this better than covering a surface with tinfoil which leaves infrared
heat out?

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wscott
Go read the other comments. This is not an insulator. It will take a source of
heat and start radiating that heat at a certain frequency where our atmosphere
happens to be transparent. And because our atmosphere is transparent, there
isn't at heat at that frequency outside so this "window" in your house is
effectively one way.

Also, the demonstrated energy transfer density of this stuff is high enough
that the area of your roof is enough cooling to make a series dent in your
cooling cost.

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mrfusion
This would be awesome to put on cpus.

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ars
This only works because the sky does not transmit much energy at the
particular infrared frequency this operates at.

In contrast ordinary objects (the computer case, a tree, a wall), do transmit
those frequencies.

This would have no effect - it's absorbing the frequencies emitted by the
wall, and transmitting to the wall, the net effect is zero.

i.e. it only works under open sky. I suspect even clouds would block this from
functioning. (Not sure about this - maybe water has a "window" at this
frequency?)

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asafira
You are actually totally correct, clouds would worsen cooling power.

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yellowapple
Thankfully, clouds also reduce the amount of sunlight heating things up, so
that might not be an issue for, say, cooling a house.

