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Huh - I'm always interested in ways to make A/C more energy efficient. Squeezing and un-squeezing gas seems so COMPLICATED compared to how easy it is to heat th
by leggomylibro 9y ago
Huh - I'm always interested in ways to make A/C more energy efficient. Squeezing and un-squeezing gas seems so COMPLICATED compared to how easy it is to heat things up. Entropy is a cruel mistress. Anyways, it sounds like this is the important bit:
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So Raman and electrical engineering professor Shanhui Fan made panels containing layers of silicon dioxide and hafnium oxide on top of a thin layer of silver. These radiate in a unique way: They send heat directly into space, bypassing the Earth’s atmosphere. The panels do this by emitting heat at infrared wavelengths between 8 and 13 micrometers. To these waves, the Earth’s atmosphere is transparent. What’s more, the panels reflect nearly all the sunlight falling on them.
For the new fluid-cooling system, the researchers made radiative panels that were each one-third of a square meter in area; they attached the panels to an aluminum heat exchanger plate with copper pipes embedded in it. The setup was enclosed in an acrylic box covered with a plastic sheet.
The team tested it on a rootop on the Stanford campus. Over three days of testing, they found that water temperatures went down by between 3- and 5 °C. The only electricity it requires is what’s needed to pump water through the copper pipes. Water that flowed more slowly was cooled more.
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So it sounds like how space stations kick out heat; The ISS uses that sort of thing[1]. You flow coolant through things that heat up, like solar panels or a warm environment, and then you pump it into these bricks that don't absorb heat from light. The coolant warms up the bricks, which emit that heat as infrared radiation. Planetside, I guess that you can't let the infrared radiation be absorbed by the atmosphere, or it won't cool anything.
So, maybe this could take the compression out of our current cooling systems - compress/heat up, expose to outside temp, let cool, decompress/cool, expose to inside temp, repeat.
My main question would be, is it capable of cooling beyond the ambient outside temperature? If so, how? I might be misunderstanding or missing something about how the 'blasting energy away as IR radiation' thing works.
[1]: http://www.lockheedmartin.com/us/products/HeatRejectionRadiators.html http://www.lockheedmartin.com/us/products/HeatRejectionRadia...
- ar813 9y agoI'm one of the authors / people working on this. Yep, radiators like the ones on the ISS are pretty much the dominant/only ways to get heat out in space. In response to your questions: yes, it can in fact cool below the ambient air temperature entirely passively (even during the day! -- which adds real value for cooling applications). We've shown in other recent work that you can use this effect to cool as much as 45-50°C below the ambient air temperature, if you insulate the radiator perfectly. The reason this works here on Earth is that some upward thermal radiation isn't absorbed and re-emitted back to you. So if you start at the air temperature, looking upwards, you will be sending more heat out than the sky sends back to you. This allows an upward-looking surface to cool itself down until the heat going out and coming back to it balance out.
- leggomylibro 9y agoWow, cool. Well, thanks for doing this sort of research! Better cooling could save us a whole lot of energy :)
- bronz 9y agothis is such amazing work! how expensive are these radiators before and after scaling production? ignoring the pumps, how long should they last without repair?
- ar813 9y agoThe great thing is that we can use existing manufacturing processes (which we are already using) to do this extremely cheaply at large volumes. So the cost at scale will be competitive and make economic sense for customers. Our focus is on packaging this into a compelling product that delivers large electricity savings. Lifetimes of 20+ years are expected.
- leggomylibro 9y agoSo are those normal thin-film deposition processes? I don't know much about those, but am interested in them - are any of the materials particularly tricky to work with? Or can you just sputter the oxides one-by-one onto a silver substrate?
- killjoywashere 9y agoThanks for jumping in! How many installed square feet of real estate do I need to be equivalent to my 3 ton air conditioner (which needs 4 square feet)?
- fpoling 9y agoDoes this work when humidity is high? Water absorbs thermal infrared and emits it back.
- ar813 9y agoYou can still get cooling, but you get less heat rejection per unit area in high humidity because of the effect you point out.
- baybal2 9y agoI wonder if anybody with serious resources tried to use anti-Stokes scattering for refrigeration.
- deleted 9y ago[deleted]