
A Material That Throws Heat into Space Could Soon Reinvent Air-Conditioning - rbanffy
https://www.technologyreview.com/s/608840/a-material-that-throws-heat-into-space-could-soon-reinvent-air-conditioning/
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ChuckMcM
Same guys as the IEEE article :
[https://news.ycombinator.com/item?id=15176721](https://news.ycombinator.com/item?id=15176721)
but a bit more on the practicality of hooking it into existing systems.

One of the interesting side effects of putting a bunch of solar panels on my
roof was the shade they provide (they sit about 4" above the roof) and that
small gap of air made the attic significantly cooler than before the panels
were installed. With these on the 'north side' of the roof (not with water
plumbing, just providing a 5 degree C temperature difference) that would be
helpful in the Bay Area.

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Xeoncross
When we built our house we put the actual metal roof several inches above the
roof. The actual roof decking NEVER gets hotter than the ambient air
temperature (115F max here in Texas). Solar panels or any form of shade
structure (including trees) accomplish the same thing.

[http://tinyhousemansion.com](http://tinyhousemansion.com)

Shingles or metal directly on a roof heats the house substantially but is
cheaper (costs less in labor). That is why we still do it. (Just like dark
roofs look "nice" so we still do that too).

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ChuckMcM
Great link, and with this material you would get 5 degrees C _below_ ambient
on their underside, so nearly 9 degrees F lower.

Putting the shingles directly on the roof has benefits like keeping water out,
and a floating roof (like my panels) is much more susceptible to wind damage
(either to create a sail out of them). The 'old school' fix was of course sod
roofs. If you put enough thermal mass between the roof and the interior you
avoid significant heating.

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olivermarks
What about capturing heat form the sun in the winter? Bay Area is a good
example for that with sunny but cold days. Would those pockets of warmth we
find in winter from sheltered sunny areas and attic spaces be reflected away
too? It seems to me that capturing power from the sun in the summer and
storing in maybe possible in the future local batteries is preferable to
reflecting away the power? Or both?

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ChuckMcM
Good question, I suppose if you mounted them as strips like a shutter (but
with 180 degrees of rotation in the long dimension) you could have strips that
were black on one side and this material on the other. When you want heat you
turn the black side out to the sun, when you want cooling you put the
reflective side out.

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smsm42
From the article:

The point of jackets, mittens, and scarves is to retain as much of that
radiant heat as possible, keeping us warm on winter days.

This is AFAIK not how clothing works - excepting special ones like space
suits, firemen suits, etc. Clothes are primary to prevent convective cooling,
not radiative cooling.

5C cooling in Bay area may be enough for most of the summer outside of top
heat days in Jul-Sep. If that is substantially cheaper than installing AC, it
could be a good solution for most homes and save lots of energy.

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lordnacho
I don't get why there's a magic band that lets the heat escape? Does it happen
to be a gap in the spectra of the atmospheric gases?

Also I was wondering what the effect of plain old mirrors on people's roofs
would be. The point being to reflect the sunlight of course.

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tryingagainbro
_Also I was wondering what the effect of plain old mirrors on people 's roofs
would be. The point being to reflect the sunlight of course. _

The sun can hit the roof all day and it will not heat a normal house...so many
layers in between and the heat will not reach below.

IMO it's just a matter of time before we use the sun to offset its effects on
homes and offices. A super sunny day gives us a lot of power we could use to
cool what the sun is heating. They coincide perfectly for a lot of hours.

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djrogers
> The sun can hit the roof all day and it will not heat a normal house

This is completely false. An attic that's heated up to 130+* will have a
significant impact on the temperature of the house it's attached to unless you
use an uncommonly ridiculous amount of insulation. This is why things like
attic fans are so effective in reducing AC load...

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Synaesthesia
If this is feasible, the great thing about it is it’a entirely passive,
basically getting cooling for “free”. (I suppose you still pump a coolant
through it but that’s fairly negligible energy cost.)

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djrogers
I could see people in hot climates using these as reverse solar panels for
cooling their pools. Nothing refreshing about jumping into a 95* pool on a
100*/90% humidity day...

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gyrgtyn
Will it zap birds?

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x3n0ph3n3
My thought was blinding pilots...

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mark-r
Infrared, no blinding.

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mannigfaltig
So we're going to shoot these precious entropy differentials away into space?

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tristanj
[http://sites.gsu.edu/geog1112/files/2012/10/Energy_Balance.p...](http://sites.gsu.edu/geog1112/files/2012/10/Energy_Balance.png)

The earth already emits massive amounts of energy back into space. Nearly all
the energy received from the sun is reemitted back into space, if this didn't
happen the earth would quickly burn up. Adding reflectors won't make a huge
difference as this energy would go back into space anyway.

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prestonh
In equilibrium that's true, but the whole problem is that we're not in
equilibrium at the moment. That's what climate change is all about. If we can
increase the albedo (reflectance coefficient, basically) of the planet, we can
push the Earth down into an equilibrium position at lower temperature.

EDIT: Of course, we would have to significantly alter the albedo, which is
probably not possible with rooftop panels alone.

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tristanj
Grandparent poster is suggesting that sending this energy out to space is a
waste. It's not, if there were no reflectors, the energy will end up in space
anyway. The reflectors emit about 40 watts per square meter. In comparison,
the earth emits about 12 trillion watts per hour. So these reflectors won't
directly make any noticeable increase on the earth's total solar irradiance.

From the article, it doesn't look like increasing albedo is the researcher's
goal for these devices. It looks like they're doing this to reduce air
conditioner energy usage, which would reduce CO2 emissions from fossil fuel
burning power plants.

Also, the earth's temperature is never really in equilibrium in the first
place, as it's always heating or cooling due to the day-night cycle or
seasonal axis tilt.

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ScottBurson
> the earth emits about 12 trillion watts per hour

Delete "per hour". The watt is already a unit of energy per unit time (1 joule
per second, specifically). So 12 trillion watts is the same as 12 trillion
joules per second.

