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Nano-engineered panel passively cools buildings by emitting heat into space

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April 23, 2013

A newly-developed roof panel both reflects sunlight, and emits heat drawn from the buildin...

A newly-developed roof panel both reflects sunlight, and emits heat drawn from the building into outer space (Photo: Shutterstock)

Studies have already shown us how white-painted roofs can help cool buildings by reflecting sunlight, while "green" roofs beat the heat by blocking sunlight and providing a source of evaporative cooling. Now, a team of scientists from Stanford University have created a panel that not only reflects sunlight, but it also draws heat from within the building and emits it into outer space.

First of all, the panel acts as a highly-effective mirror, sending most incoming sunlight back from whence it came. Reflective surfaces can still get hot, however, which is where the device’s ability to emit thermal radiation (heat) comes into the picture.

When thermal radiation is blocked by the Earth’s atmosphere, it becomes trapped between the ground and outer space – this is what lies behind the greenhouse effect. The Stanford panel, however, is made from nanostructured photonic materials (including quartz and silicon carbide), that cause the radiation to be emitted at a wavelength at which the atmosphere is virtually transparent. This allows the radiation to pass freely through, into the freezing vacuum of outer space.

The panel is capable of a net cooling power of over 100 watts per square meter (10.8 sq ft). According to the researchers, this means that “a typical one-story, single-family house with just ten percent of its roof covered by radiative cooling panels could offset 35 percent its entire air conditioning needs during the hottest hours of the summer.” What’s more, the panels are completely passive, with no moving parts and not requiring any power source (including the sun) to operate.

It’s also conceivable that the cooling panels could take the place of solar panels, currently used to generate electricity to run air conditioners. Beyond the commercial applications of the technology, the researchers believe it could make cooling possible in off-grid areas or equatorial developing nations, where air conditioning is currently impossible. It could even be used to help keep parked cars cool.

The panel was developed by Professor Shanhui Fan and his graduate students Aaswath Raman and Eden Rephaeli. A paper on their research was recently published in the journal Nano Letters.

Source: Stanford University

About the Author
Ben Coxworth An experienced freelance writer, videographer and television producer, Ben's interest in all forms of innovation is particularly fanatical when it comes to human-powered transportation, film-making gear, environmentally-friendly technologies and anything that's designed to go underwater. He lives in Edmonton, Alberta, where he spends a lot of time going over the handlebars of his mountain bike, hanging out in off-leash parks, and wishing the Pacific Ocean wasn't so far away.   All articles by Ben Coxworth
10 Comments

Sounds good, but what do you do in winter?

Ozuzi
23rd April, 2013 @ 07:29 pm PDT

sounds like money for nothing ... radiation at frequencies that are not absorb-able by the atmosphere sounds like wishful thinking ...

Jeffrey J Carlson
23rd April, 2013 @ 11:23 pm PDT

Great for tropical countries.

thk
24th April, 2013 @ 01:07 am PDT

I call bunk on this. Silicon carbide has an emission spectrum of between 3-15 microns, quartz is between 2-8 microns. This spectrum is in the blackbody infra-red band mostly captured by water vapour, and partially by CO2.

(Yes, water vapour is a more potent greenhouse gas than CO2 - wider absorption spectrum, higher specific heat capacity)

Unless this material is somehow so finely calibrated that it emits IR radiation in one of the narrow absorption troughs not covered by the overlapping absorption profiles of H2O and CO2, with tolerance of /- 0.5 micron, then I doubt the validity of the concept.

Interestingly, if you look at an atmospheric absorption spectrum chart the only band of the spectrum which is almost completely transparent is between the ultra-violet and infra-red range, otherwise known as 'visible' light....

PeetEngineer
24th April, 2013 @ 01:15 am PDT

It does not go well with the typically necessary insulation, I suspect. Also the spectrum thing sounds a bit far-fetched. Not going to be a mainstream product, in my opinion.

martinkopplow
24th April, 2013 @ 02:30 am PDT

Remotely related, I took a infared themometer out on my balcony one night. The outside air temperture was in the low 80 Deg's F , pointed at the clear night sky the thing indicated 17 Deg. F Your Solar cooker by day, might be usable as a Outer Space cooler by night.

Dave B13
24th April, 2013 @ 06:32 am PDT

My view here is why remove the heat? Why not using thermocouple technology turn that heat into energy to be used to power the building? as well as storage for when it is colder, and to keep building hot water, well...hot.?

yinfu99
24th April, 2013 @ 09:06 am PDT

Sorry, but until a Geo-stationary satellite (or satellites) picks up your "emitted heat" I'm not convinced that nano-technology or any other material can support such a claim. More likely you are only reflecting some of the solar radiation into the atmosphere while creating a heat-sink on the rooftop. Better mount these puppies at least a meter from any flammable/melt-able materials.

Mirmillion
24th April, 2013 @ 03:15 pm PDT

This could reduce the heat island effect of cities, but it could cause an ice age like predicted in the 1970s.

re; PeetEngineer

Lasers emit on a really narrow frequency band so if you do not focus the energy into a beam but use the same emitter medium you will have the same bandwidth and if it is alined right out the energy goes.

re; yinfu99

The cost of harvesting the energy might be higher than the energy is worth. Sometimes simply dumping is the most cost effective solution.

re; Ozuzi

Don't pump the heat into the radiators.

Slowburn
24th April, 2013 @ 04:21 pm PDT

The moment I saw the picture, my mind just screamed

YYYYYEEEEEEEAAAAAAHHHHHHHHHHHHHHHHHH!

and The Who took over from there.

Nacho Lotitto
24th April, 2013 @ 09:11 pm PDT
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