Stanford engineers invent high-tech mirror to beam heat away from buildings into space

[IDemo]

Stanford engineers have invented a revolutionary coating material that can help cool buildings, even on sunny days, by radiating heat away from the buildings and sending it directly into space.

A team led by electrical engineering Professor Shanhui Fan and research associate Aaswath Raman reported this energy-saving breakthrough in the journal Nature.

The heart of the invention is an ultrathin, multilayered material that deals with light, both invisible and visible, in a new way.

Invisible light in the form of infrared radiation is one of the ways that all objects and living things throw off heat. When we stand in front of a closed oven without touching it, the heat we feel is infrared light. This invisible, heat-bearing light is what the Stanford invention shunts away from buildings and sends into space.

http://news.stanford.edu/news/2014/november/radiative-cooling-mirror-112614.html

[ellennelle]

1. why do that???

what a waste!! why not convert the heat to re-usable energy??

stanford, home of the heritage foundation.

[4dog]

2. Probably not practical entropically

That is, it's not very concentrated.

[OKIsItJustMe]

3. Ah ha! I knew it sounded familiar!

It’s sounds like an update of this story: http://www.democraticunderground.com/112739564

[Control-Z]

4. I have been thinking, wondering,

about the possibility of something like this. I know polar ice reflects heat away from the planet so it serves more than one purpose in contributing to the earth's climate. Without the ice it will no longer play a part in helping to cool the planet. I hope some kind of technology, maybe along these lines, could be put into place to help slow down or stop the ice melt.

[Fumesucker]

5. I have a non contact laser guide thermometer

If you point it at the sky away from the sun on a warm but cloudless summer day it will read well below freezing, the clearer it is and the less moisture/haze in the air the lower the temperature reads.

That mirror will work well where it's mostly cloudless, clouds are going to get in the way of getting rid of heat by infrared radiation though.

[muriel_volestrangler]

6. I think the main purpose is to reduce the need for air conditioning in the building

rather than the total radiation absorbed in the whole area. It's warm, sunny days when it would most be needed, too.

[OKIsItJustMe]

7. As I recall, they take clouds into account

[font face=Serif][font size=3]…

Using engineered nanophotonic materials the team was able to strongly suppress how much heat-inducing sunlight the panel absorbs, while it radiates heat very efficiently in the key frequency range necessary to escape Earth’s atmosphere. The material is made of quartz and silicon carbide, both very weak absorbers of sunlight.

…[/font][/font]

http://pubs.acs.org/doi/abs/10.1021/nl4004283

[font face=Serif][font size=5]Ultrabroadband Photonic Structures To Achieve High-Performance Daytime Radiative Cooling[/font]

…

[font size=4]Abstract[/font]
[font size=3]
If properly designed, terrestrial structures can passively cool themselves through radiative emission of heat to outer space. For the first time, we present a metal-dielectric photonic structure capable of radiative cooling in daytime outdoor conditions. The structure behaves as a broadband mirror for solar light, while simultaneously emitting strongly in the mid-IR within the atmospheric transparency window, achieving a net cooling power in excess of 100 W/m2 at ambient temperature. This cooling persists in the presence of significant convective/conductive heat exchange and nonideal atmospheric conditions.

…[/font][/font]

[Fumesucker]

8. On a clear night where the air temperature is above freezing you often get frost on the ground

If it's cloudy at the same temperature then there is no frost because the clouds block the infrared from escaping to space.

http://mynasadata.larc.nasa.gov/804-2/1035-2/

Sunlight warms soil, rocks, plants, roads, buildings and bodies of water, all of which then emit the solar energy they absorb in the form of thermal (infrared) radiation that we perceive as heat. If there were no atmosphere, the Earth surface would release as much energy to space as it receives from the sun. But that would keep the Earth much too cold for life as we know it to exist.

The atmosphere is why the Earth is warm enough to support life, for it contains water vapor, a gas that strongly absorbs infrared radiation. This water vapor is the key to why the Earth is warm enough to support life. According to the National Oceanic and Atmospheric Administration, removing water vapor from the atmosphere would reduce the average temperature of Earth to 0 degrees F! The oceans would be frozen solid. The Irish scientist John Tyndall was among the first to explain this, and in 1863 he wrote,

Aqueous vapour [water vapor] is a blanket, more necessary to the vegetable life of England than clothing is to man. Remove for a single summer night the aqueous vapour from the air which overspreads this country, and you would assuredly destroy every plant capable of being destroyed by a freezing temperature. The warmth of our fields and gardens would pour itself unrequited into space, and the sun would rise upon an island held fast in the iron grip of frost.

[OKIsItJustMe]

9. Clouds block infrared frequencies, but not all infrared frequencies

http://www.giss.nasa.gov/research/briefs/schmidt_05/

…


Outgoing spectral radiance at the top of Earth's atmosphere showing the absorption at specific frequencies and the principle absorber. For comparison, the red curve shows the flux from a classic "blackbody" at 294°K (≈21°C ≈ 69.5°F).

…

[OKIsItJustMe]

10. Material Cools Buildings by Sending Heat into Space

http://www.technologyreview.com/news/532826/material-cools-buildings-by-sending-heat-into-space/

[font face=Serif][font size=5]Material Cools Buildings by Sending Heat into Space[/font]

[font size=4]A new material that requires no electricity uses the universe as a heat sink—even when the sun is shining.[/font]

By Katherine Bourzac on December 1, 2014

[font size=3]A material that simultaneously reflects light and radiates heat at frequencies that vent it through the Earth’s atmosphere could one day help cool buildings on hot days. The material cools itself to a temperature below the ambient air, and has been tested on a rooftop at Stanford University by its inventors, who are now working on scaling up the design.

…

Usually the way to let something cool off is to put it somewhere cold; the hot object will radiate its excess heat into the surroundings. Fan’s material becomes cooler than its surroundings by reflecting light and emitting heat at carefully tuned frequencies. The material emits heat at frequencies that match the planet’s “thermal window”—from eight to 13 micrometers—which lets it pass through the atmosphere and into space. It effectively cools down by using outer space as a heat sink.

…

To demonstrate the weird properties of this layered material, the Stanford researchers compared it to silicon painted black—a good thermal radiator—and aluminum—a good reflector. The passive cooler design is described today in the journal Nature.

…

Fan says covering an entire roof with the material should eliminate the need for air conditioning. The group plans to leverage manufacturing technology that’s used to make coated windows, and it might be possible to make the material, which is only about two micrometers thick, on lightweight plastic films for easier installation. But the next step is a modest one: they’ll to go from the eight-inch demo to a square-meter tile of the material.[/font][/font]

http://dx.doi.org/10.1038/nature13883