A film that can cool buildings without the use of refrigerants

http://www.economist.com/news/science-and-technology/21716599-film-worth-watching-how-keep-cool-without-costing-earth

by feelthepain • 9 years ago

184 100 9 years ago

jrockway• 9 years ago

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

_rpd• 9 years ago

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.

waqf• 9 years ago

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

woodandsteel3• 9 years ago

I could be wrong, but the film is described as so simple that it seems like it could be in commercial production a lot sooner than that.

gewa• 9 years ago

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

milcron• 9 years ago

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.

a_t48• 9 years ago

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

caf4• 9 years ago

Because it's radiating the heat out into space, you need to consider the entropy of the complete Earth-Space system, which is actually increasing.

cgriswald2• 9 years ago

Entropy is decreasing locally, sure, but the Earth is not an isolated system, so it's not violating the second law.

voltagex_• 9 years ago

http://science.sciencemag.org/content/early/2017/02/08/scien... is the paper linked in the article

Retric6• 9 years ago

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.

rickdale• 9 years ago

Making the absolute best it can do the equiviemnt of a fan on the roof which can't replace AC.

You are right it won't replace the AC, but the technology could lead to a reduction in overall AC use.

caf4• 9 years ago

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.

samch5• 9 years ago

Reading the article helps. One of these tarps cooled a container of water underneath it by 8°C during an overnight test:

"We further demonstrate the effectiveness of radiative cooling for a relatively large thermal mass using water as a cold storage medium. A plastic water tank was placed underneath the radiative cooling glass-polymer hybrid metamaterial, putting water in close contact with the heat-conducting copper plate. Since the water is stationary in the experiment, its large heat capacity substantially slows down the cooling process. We therefore used a 10-µm-thick HDPE film on top of the Polystyrene foam box in this setup to reduce convective heat loss and improve thermal isolation. The water temperature continuously dropped, reaching more than 8° C below ambient after two hours of exposure."

sqeaky• 9 years ago

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.

wccrawford• 9 years ago

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.)

asafira4• 9 years ago

So that's definitely a limitation, but I wouldn't call it an issue --- this would have plenty of application!

mrfusion3• 9 years ago

This would be awesome to put on cpus.

elbigbad• 9 years ago

Don't CPUs not usually play friendly with water?

wallacoloo• 9 years ago

The water exists only to transfer the heat over distance. If the heat sink and heat source are in direct contact, then no need for water.

euyyn• 9 years ago

I expect the radiated IR would just heat the device around the CPU. It's not like CPUs usually face outer space.

ars• 9 years ago

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?)

asafira4• 9 years ago

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

Vendan2• 9 years ago

8 to 14 microns is called the "atmospheric window", and a large portion(up to around 80%, from what I've seen) of energy at these wavelengths escapes the atmosphere. This window is a result of weak absorption by carbon dioxide and water, thus the IR emissions will pass right through clouds.

zer0t3ch• 9 years ago

Not really. I doubt it's better than the existing CPU coolers we use, CPU coolers just aren't practical for cooling buildings.

mrfusion3• 9 years ago

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

averagewall2• 9 years ago

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.

cgriswald2• 9 years ago

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.

stuaxo• 9 years ago

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.

awqrre• 9 years ago

isn't air temperature control the largest energy expense in most countries' homes?

Baeocystin3• 9 years ago

Yes. Although IIRC it is heating, not cooling, that consumes the lion's share. But the general point stands.

tajen2• 9 years ago

I'd be curious about France for example, since air conditioning isn't as widespread as in Germany, Thailand or USA.

sfifs3• 9 years ago

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.

ro_sharp• 9 years ago

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-...

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

dreamcompiler3• 9 years ago

Not in the American South. Every room of every building in Texas has A/C blasting in the summer.

deerpig• 9 years ago

Having lived for 30 years in SE Asia, with temps in the mid-forties C during the hot season (which will start very soon) we seldom turn on the aircon for more than 1-2 hours at the most at night, and then only in the bedroom.

This works if you have good fans and a lot of icewater. Using aircons too much ends up making you sick, going in and out of the heat. In Thailand we had two golden retrievers who had their own fans in the coolest parts of the house, they would sleep through the heat and then be very active in the early morning and evening.

It should also be mentioned that we are far enough south that the length of day and night doesn't change that much over the year -- the night is always long enough for radiational cooling to do it's job. That is not the case in places like New York or Boston where the nights are so short in August that it never cools down. It's always comfortable in the morning here before the mid-morning heat hits.

Contrast this with visiting hot parts of the United States where you go from your airconditioned house to your airconditioned car to your airconditioned big box store to your air conditioned office. That's a terrible way to live.

tajen2• 9 years ago

Not only that, but the energy is radiated in wavelengths that aren't absorbed by the atmosphere (I suppose it's different with cloudy skies). If this solution becomes massively widespread, it could have a good effect on global warming.

With caveats: If we imagine a city radiating all its energy as infrared, it could cause weather abnormalities.

lovemenot2• 9 years ago

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.

azinman2• 9 years ago

Omg amazing. Good find! :)

clort• 9 years ago

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.

Udik• 9 years ago

Apparently, they improved on the work originally done by Dr. Fan in 2014.

agumonkey• 9 years ago

Add them to wikipedia aptronym list.

caf4• 9 years ago

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

sfifs3• 9 years ago

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

adiabatty• 9 years ago

Death Valley, California. I tried swimming in a pool there once and it was like swimming in a jacuzzi.

caf4• 9 years ago

Far North Queensland is one I've been to.

sparrish• 9 years ago

In Phoenix AZ, July/Aug/Sept pool parties are often BYOBOI (bring your own block of ice). Everybody brings a 10 lb. block of ice to throw in the pool and within an hour it's cool enough to enjoy, even in the 115F heat.

dxhdr2• 9 years ago

"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?

pdonis2• 9 years ago

Recycle it.

dxhdr2• 9 years ago

We don't recycle microplastics for a variety of reasons, that's the reason I bring the issue up. Current theory is microplastics end up in our food.

asafira4• 9 years ago

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.

DiabloD3• 9 years ago

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

woodandsteel3• 9 years ago

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.

ph0rque2• 9 years ago

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.

CamperBob2• 9 years ago

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.

Gibbon1• 9 years ago

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.

sfifs3• 9 years ago

I don't know about this particular technology but as a parallel all Florescent Lights operate on a similar concept. They absorb radiation at frequency X and emit in frequency Y where Y is visible light.

It appears that the researchers have tuned the emission to a frequency that is not reabsorbed by the atmosphere but emitted unimpeded into space. Pretty clever engineering.

samch5• 9 years ago

I'm not entirely sure about the mechanism, but it appears to work via phonon-polariton resonance:

https://en.wikipedia.org/wiki/Polariton

So, couple this, in terms of the dispersion of energy: "Our hybrid metamaterial is extremely emissive across the entire atmospheric transmission window (8-13 μm) due to phonon-enhanced Fröhlich resonances of the microspheres."

And this in terms of the absorbtion: "In the case of large microspheres, modal interference between higher order modes makes the hybrid metamaterial strongly infrared-absorbing."

And finally this in terms of reflectance: "The hybrid metamaterial strongly reflects solar irradiation when backed with a 200-nm-thick silver thin film prepared by electron beam evaporation... The measured spectral absorptivity (emissivity) of the sample (Fig. 3D) indicates that the 50-μm-thick film reflects ~ 96% solar irradiation..."

WallWextra• 9 years ago

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

Baeocystin3• 9 years ago

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.

vanderZwan2• 9 years ago

Wouldn't the latter effectively be equivalent to sand?

asafira4• 9 years ago

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...

ChuckMcM2• 9 years ago

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.

manmal• 9 years ago

Do you mean 2% or 2 percent points?

ChuckMcM2• 9 years ago

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

ainiriand• 9 years ago

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

wscott• 9 years ago

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.

ChrisFoster• 9 years ago

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.

jsilence2• 9 years ago

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.

ph0rque2• 9 years ago

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

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

jsilence2• 9 years ago

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

jbmorgado• 9 years ago

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?

A film that can cool buildings without the use of refrigerants

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