Material Cools Buildings by Sending Heat into Space | Hacker News Reader

Material Cools Buildings by Sending Heat into Space

technologyreview.com

36 pointsRylinks18 comments

I'm no scientist, but would there be a way to combine this with solar panels to also produce electricity? It seems the goals are counter to one another, but it would really be amazing to accomplish both with one panel.

Since the device emits energy within a narrow range, perhaps it be possible to build a top-most layer that acts like an antenna for that range? Then you'd have a pump that absorbs heat from the environment, squeezes in into a narrow band, and emits it into a wire.

Or, I suppose you could park a Stirling engine on it and generate power from the thermal gradient it must be producing.

I think you could combine the two in parallel. A problem with solar panels is that their efficiency drops as they heat up. It might be cost effective to use these panels as heat sinks for a solar panel for passive cooling.

That said, the material is specified to have a cooling capacity of ~40Wm^-2. You normally assume something like ~800-1000Wm^-2 for incident solar radiation, so I'm not sure how economical using something like this with a solar array would be.

Really cool though.

Put the solar panel on top of it at an angle. The roof will keep radiating heat, and some of it will hit the bottom of solar panel, but that's probably ok. Maybe can put reflective material on the bottom of the solar panel so it bounces around until it finally escapes.

At the very end of the methods section, they write: "Future designs and configurations may find ways of using this reflected sunlight, enabling shorter payback periods and lower levelized costs." I don't have any idea what they have in mind.

This same group is also trying to solve a related problem, which is how to keep solar panels cool, since they are less efficient when they heat up. They have designed coatings that are transparent to sunlight and dump heat to space ( http://www.opticsinfobase.org/optica/fulltext.cfm?uri=optica... )

If it is used on top of a building certainly the defrosting features of masts and other fittings look mootable; skylights have shades; you can use the stuff as the concentrating optic of your choice, so to choose smaller water or thermovoltaic systems, heat and circulate the pool (hot tub) on the roof, etc. Taken to architectural limits, thermal cycling wear on all roofing is lessened. Silage and water loop uses exist as LEED elements, and the swept radiant flux can even agitate self-cleaning glass.

One wonders if that this is used extensively in urban areas, could it mitigate the urban heat island effect to some extent, and in doing so offset some amount of measured global warming?

Here's a link to the original article in Nature under their new [0] free read-only access policy:

http://rdcu.be/bKmA

[0]: http://www.nature.com/news/nature-makes-all-articles-free-to...

So if, in the future, this material was in heavy use atop buildings and dwellings across the planet, and the heat is all being radiated out the same thermal window, does this mean that at some set distance from the earth, there's a ring of extreme heat being generated?

I'm probably missing something in the definition of "thermal window".

The thermal windows refers to the fact the earth's atmosphere is pretty good at letting through longer wavelength IR than shorter wavelength IR.

http://en.wikipedia.org/wiki/File:Atmosfaerisk_spredning.png

As an example. Visible light is that little bit all the way to the left. That entire big chunk on the right is the thermal window that they're talking about.

> a ring

Well, a sphere of expanding energy, anyway. Just like the shell of TV broadcast energy that leaves the planet. Also, we rotate and move in space, so less of a sphere and more like a windy tube.

I wonder if this would be useful for spacecraft?

Surfaces optimized for reflecting and emitting light/heat are indeed used on spacecraft ( http://en.wikipedia.org/wiki/Optical_solar_reflector )

However you wouldn't have to worry about optimizing these for the atmospheric IR window, as you do on earth, which is the advance claimed in this paper.

What happens if it gets dirty / rained on?

The same thing that would happen with glass windows and solar panels. They would eventually be cleaned.

So... a mirror?

Yes, but in addition to being a mirror, it absorbs heat energy and emits it as infrared light in specific frequencies.

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