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.
So it sounds like how space stations kick out heat; The ISS uses that sort of thing. 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.
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.
This would allow for a really low cost refridgerated/temp-controlled containter. Then have a small requirement for a solar panel to pump some fluids. The result would be the ability to have shipping containers that can maintain temps with extremely low cost/energy requirements and you might revolutionize the ability to ship foods around places like Africa.
Also - can this be applied in any way as a "paint"? Such that you paint cars, roofs or whatever with this?
That's incredible! Isn't that enough to run a heat engine on? If so, does this allow you to extract (nearly) free energy out of the ambient heat?
I ask because as someone who has lived most of his life in southern Florida, this kind of device could reduce electricity bills massively around here, as long as the humidity isn't too much of a problem
I don't quite understand what that means. If your radiator is supposed to radiate away the surrounding heat, shouldn't it on the contrary be connected as much as possible to the environment?
what they're doing here is shifting the transmission characteristics of radiation to be within the infrared window (https://en.wikipedia.org/wiki/Infrared_window) so that it's kind of like surrounding air (and water vapor, most importantly) aren't present at all and you're radiating in to the giant cold heatsink that is space.
Conduction, convection and radiation.
1) Does it emit more IR at higher temperatures? In other words, would pumping hot water through/under it produce larger temperature drops?
2) Is it weather proof, or do you still need to find a coating that protects it while not blocking the IR?
It's pretty durable on its own. That being said, as we've moved to the product stage we've packaged it in a way to protect it further.
That said, we are talking about something that has a weird radiance spectrum as a selling point, so, expect some deviation from the standard T^4 curve.
Also, removing heat from the Earth is probably a positive at this point in time.
You need to cool the building anyway, so the added energy from displacing the beam to a (presumably turbine) generator would essentially be 'free.'
This is more efficient than the photovoltaic because you don't have to produce install and maintain a photovoltaic (all of which costs some energy), and you were going to cool this building with this method anyway (so there's little downside to harvesting the energy aside from complexity, which is a concern).
I assume you'd need line of sight from the panel to the generator, which it does seem would be tricky, but doesn't seem insurmountable. (Put the collector on a tower for example, in most areas of the country I think it wouldn't have to be higher than a few hundred feet). It just depends on how much heat you're displacing and whether you can collect enough to run the generator.
If it were "I'm just trying to produce energy", I'd agree that the photovoltaic is better, but if this system happened to be dual use and doing two things we already want to do, it seems like it would be a pretty substantial win.
This also ties into why a magnifying glass cannot make something hotter than its source of light.
"Lenses and mirrors work for free; they don't take any energy to operate. If you could use lenses and mirrors to make heat flow from the Sun to a spot on the ground that's hotter than the Sun, you'd be making heat flow from a colder place to a hotter place without expending energy. The second law of thermodynamics says you can't do that. If you could, you could make a perpetual motion machine."
The "beam" this generates is really more of a floodlight than a spotlight, so only a tiny part of the energy would hit your satellite. If you could focus it down to a narrow beam which hit only your satellite, my gut feeling is that you would simultaneously be focusing the surface heat of the satellite onto your panel. So once again, your panel would only "see" a hot surface, and would lose the benefit of cold space.
Also, as others have calculated in other comments, the amount of energy coming from the sun dwarfs what these panels radiate, so you are better off just pointing your satellite collectors at the sun.
Especially in space! We lose a good amount of irradiation energy from the sun to the atmosphere.
Even a power station doesn't bother trying to use that for anything.
A common use is space heating in buildings in winter, but you won't be running an air conditioner in that case, nor will your neighbors want it.
It's not that the heat isn't useful, or even that it's not a large amount of heat. It's that the heat is in the wrong place, and they need to efficiently get rid of it.
I'd have to recheck al the assumptions here because I put high odds that I constructed this back of the envelope set of numbers with some mistake in it...
What I am missing?
It's also not like other wavelengths are reflected right back, but when the atmosphere can absorb them, it will also emit them. (Radiation tends to be symmetric like that.) Conversely, the emitting panel will absorb this radiation, until equilibrium is reached.
That means that you need to use wavelengths where the air isn't literally glowing, if you want radiation cooling to work at all.
Or can you just sputter the oxides one-by-one onto a silver substrate?
And when it isn't as hot out, you can actually use the ground temp to radiate heat out of the house by itself, no need for coils and a fan to run in ambient air temp, right?
For a home aircon it might be OK, however the London Tube is having serious problems with this where many of the tube tunnels have warmed from around 14C to nearly 30C (57-86F) over the last 100 years. Leaving many of them quite hot. The surrounding ground around the tubes has warmed up and effectively heat soaked.
Heat is generated from a number of sources including diesel engines however apparently a large portion of the heat is generated by braking for each station. They've improved that by using electric regenerative braking now which in some cases can dump the power into other trains that are accelerating at the same time.
Some of the newer trains now also have air conditioning inside the trains, while that helps inside the train it doesn't help outside the train where even more heat is dumped.
Anyway for more information there is a good youtube video I can't find right now, so you could read this instead:
The other day, when it was 106F outside and I had to dry some clothes, I found it quite unfortunate that I was spending a bunch of energy to move hot air out of my house, while at the same time spending a bunch of energy creating hot air in my house to dry my clothes.
It would have been so nice if there were a reasonable way for me to take the heat already in my house and push it through the dryer.
(I could have hung them to dry, but I live too close to the freeway to do that -- they would have been dirtier than when I washed them)
In the US, but have been running Bosch condensation dryers for over a decade. Previous rental had one and the immediate difference I noticed was how much longer my clothes lasted from the cooler temps, so when I moved I bought my own W/D. No regrets.
Of course, only works for electric!
Also worth noting that dryers usually vent outdoors so they don't dump all the heat inside, where you'd then have to use the AC to remove it.
(2,842 cubic meters in liters)/365 = 7.7k liters.
The USGS  estimates 23,800 mega-gallons per day for domestic use by 268 million people. This is about 89 gallons or 336 liters per day per person.
Meat consumption accounts for 30 percent of the American figure, and sugar consumption is responsible for another 15 percent
> Similar to a geo-exchange (or geothermal) system, heat pumps transfer thermal energy from the warm sewage supply to a higher temperature range that’s effective for residential space heating and domestic hot water. While similar in concept, sewage heat recovery is more efficient and cost effective than typical geo-exchange systems. The heat source (raw sewage) has a higher temperature than ground-source heat (on average 18 degrees Celsius as opposed to 8), so it requires less energy to upgrade. Secondly, accessing the sewer line is less invasive and less capital cost intensive than drilling into the earth to access geothermal heat. It also utilizes a continuous supply of waste heat, closing the loop on a fundamental energy >> waste >> energy stream. 
I was only thinking of it in context of using the ground to sink heat, not as a real implementable plan. I think it goes without saying that the heat-pump-as-a-water-heater idea is far more pragmatic.
There are other systems for people with the land which may be less expensive which don't require drilling.
I spent several summers installing these systems, they are surprisingly simple and effective.
Power plants and ACs are not 100% efficient; the power plant converts chemical/nuclear/mechanical energy into electrical energy, releasing heat from work lost.
Your AC will convert electrical energy to cool the air around you, but because it is not 100% efficient, the total temperature of the system will rise.
There needs to be a way to get rid of that lost energy and remove it from the system. If you put that into the ground, it's still in the system. Ofc, even when they try to 'beam the heat to space', much of it will end up staying in the system (earth) as it reflects on clouds / water vapor, etc.
This is the main reason why it suddenly gets so cold at night. From a radiative perspective, you might as well be facing a ceiling of Arctic ice above you.
I'm an amateur astronomer. When I do observations at night, I always add an extra layer of clothing. It's amazing just how really cold it gets when all you do is sit under the clear night sky.
When it's cloudy it's different. The chill effect due to the (lack of) radiation is much less intense.
> According to this article in Rail Magazine, the average temperature inside the tunnels was around 14° in 1900.
> increased the temperature of the surrounding clay so much that, today, average tunnel temperatures are between 20-25°C.
There are limits to the technology. Skyscrapers are simply too large for any reasonable number of wells to provide adequate heating and cooling, Mr. Orio said. And it would be very difficult to install a well beneath an existing structure.
a typical home of 2500 square feet, with a heating load of 60,000 BTU and a cooling load of 60,000 BTU will cost between $20,000 to $25,000 to install.
I would love to see self contained shade structures that would both shade and lightly cool the air underneath them.
So, to a first estimate, no. It's absolutely beyond what we're capable of. To a second estimate: these panels reject 70 W/m^2, so to counteract current warming we would need to cover .625% of the earth's surface in them, which is 3.2 million square kilometers, which is over 6x the area you'd need to replace all of humanity's energy use with solar power.
All in all, it doesn't make much sense.
If you have a square 1 m^2 solar panel, and a square 1 m^2 area to put it in, and you live at 35 degrees north latitude, you angle your panel up 35 degrees facing south. That gives you .428 m^2 of area, angled at 55 degrees, facing north, which will always be in the shadow of the panel. So stick a rectangular infrared radiator behind the solar panel.
So the area needed would be less than that needed to replace all of humanity's energy use with solar power, but the exact amount less depends on the latitude at which you place the solar panels.
I really wish HN had some mechanism of extra upvotes, e.g. by being allowed to hand out one extra upvote per day or week, or by paying 5 cents (eur/usd) to buy an extra upvote (with a maximum of X per post or Y per day, or both, or whatever)... but alas.
A quick fix might be to just add another item to the "Lists" link at the bottom that shows the top "Favorited" comments, based on how many people have it as their most recent (or 10 most recent) favorite.
What about plain mirrors? How efficiently do they reflect photons back into space? Presumably they're highly efficient for visible light; how easy is it to reflect infrared passively?
Shiny things are great at reflecting incident radiation (which is why they're good mirrors) but bad at radiating their own heat. Dull black things are bad at reflecting but good at radiating. The technical terms are reflectance, absorptance, and emissivity.
You could even imagine a combined product which would be a corrugated panel alternating "uphill" solar and "downhill" radiator segments with the dimensions tailored to the latitude. This could be installed flat on the roof.
There are also misting units that use approx 1-2 gallons of water a day (equivalent to a toilet flush) that can also reduce energy consumption by up to 30%.
Simple solutions for big savings.
Moneyquote: "The temperature of the surrounding air has a much bigger effect on cooling efficiency than direct solar gain, and the volume of air pulled in by an air conditioner is huge."
An AC Condenser sitting in the Sunlight will naturally be a lot hotter in temperature than one sitting in the shade. For example park your car in the sunlight and then park your car in the shade? Where will the surface of your vehicle be hotter/cooler? It has nothing to do with air temperature at this point. It is the heat of the sunlight that is raising the temp of the coils in the condenser just like it would raise the temp of the surface of a vehicle parked in the sun instead of the shade.
I live in TX. I have some experience with this.
This means that you can save at most 5% by putting the radiator in the shade.
(Metal sheets heat up quickly in the sun because they have low heat capacity. They also cool down quickly if you blow on them with a fan. Just because something feels "hot", it doesn't mean that a lot of energy is stored inside)
Anyone able to do the math? Keep in mind all the billions we spend on hurricane damage.
This reminds me of sun free photovoltaics. Somehow people managed to transform heat into coherent IR waves that could be converted by the usual PV cells.
And the sun will just get warmer anyway. It is folly to think we can play God. Climate change is normal, and natural. It has been happening since the beginning of time, and will continue long after all traces of life on Earth are gone. Who are we to attempt to interfere?
Again, imagine the amount of fossil fuel needed for mining, manufacturing, transportation, of a reflective panel that can cover 10% of the earth's surface. If indeed CO2 is at the root of this problem, ask yourself if the shade given by this sun shield would offset the manufacturing costs in terms of CO2 release.
It would be more effective to simply plant more trees, or protect the Amazon from logging or somehow convince China to stop building coal-fired power plants, or the whole world to convert to nuclear power. etc.
Or just build a ladder to the moon. This is silly.
They are already convinced: https://www.csmonitor.com/World/Asia-Pacific/2017/0303/China...
I don't think so. There's not a lot of evidence "they" (meaning the CPC) are convinced of global consequence to stop. The desire for growth outweighs any actual concern for the future of the planet from their perspective. Without direct evidence of outcome, a tyrannical social structure operates from the top, expecting to deal with the future by sacrificing the bottom. The Aztecs, the Pharaohs, the Romans, USSR etc all fell when they external sources overwhelmed the existing mitigation methods (insidiously or violently) and China will probably travel the same route. One might hope it's not the final lasting dynasty 100 years from now.
...or better yet...
So... you could just do that.
Cooling systems consume 15% of electricity generated globally and account for 10% of global greenhouse gas emissions. With demand for cooling expected to grow tenfold by 2050, improving the efficiency of cooling systems is a critical part of the twenty-first-century energy challenge. Building upon recent demonstrations of daytime radiative sky cooling, here we demonstrate fluid cooling panels that harness radiative sky cooling to cool fluids below the air temperature with zero evaporative losses, and use almost no electricity. Over three days of testing, we show that the panels cool water up to 5 ∘C below the ambient air temperature at water flow rates of 0.2 l min−1 m−2, corresponding to an effective heat rejection flux of up to 70 W m−2. We further show through modelling that, when integrated on the condenser side of the cooling system of a two-storey office building in a hot dry climate (Las Vegas, USA), electricity consumption for cooling during the summer could be reduced by 21% (14.3 MWh).
And you can read the full article via sci-hub to get all the experimental details.
You don't just get electrical savings. Unlike other AC heat transfer systems, the heat is not pumped into the local surroundings, but is ejected from the Earth.
Can someone translate that into layman terms? The chained negative exponents are somewhat confusing. I would think 70 W m^2 would me square meters, but what's 70 W m^-2? I assume it's not really mappable to dimensions at that point...
> 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.
A little further research shows that the atmosphere is opaque at numerous wavelengths and it's probably safe to assume that they intentionally targeted the opaque ones: https://i.imgur.com/eUmTltm.png
A title is a title. And the title claims 'heat' not reflecting infrared wavelengths between 8 and 13 micrometers. And imho 'heat' is more then certain ranges of infrared wavelengths. So in that sense i can see why somebody uses the word clickbait in regards to this title.
While i'm just afraid the moon will start to condensate
Furthermore, regarding cloud cover, I am dubious of the premise that even the specified wavelengths penetrate otherwise opaque cloud cover. Sure, maybe that portion of the spectrum penetrates the typical atmospheric mix, including light water vapor, on an otherwise clear day, but, color me unsurprised if it fails to penetrate smog, diesel and particulate pollution, and other common dust constituents in cloud nuclei. I mean, even radar can be blinded by dense storm clouds.
But hey, maybe I'm wrong, maybe it's a 100% miracle cure. Maybe it's that awesome. I hope I really am just a big dummy, too lazy to read a blurb more than three sentences long.
Then ask for a summary, or point out that it's not well written for easy dissemination of facts.. There's no need to call a title out as click bait when it isn't. There's plenty of click-bait titles to go around, we don't need to malign accurate titles without cause. A click-bait title isn't just wrong or unclear, it's purpose is to intentionally mislead people for views. An accusation of click-bait is similar to an accusation of lying, which is different than being unclear or incorrect. As such it should be reserved for cases where there's evidence to back it up, otherwise discourse breaks down, in the same way accusing someone of lying when they are unclear (or you are unclear on their meaning) doesn't lead to useful discussion.
You have questions regarding the veracity of the statement? Sure, figure that out, and then make a statement about how accurate it is. If you aren't part of the signal, you're part of the noise.
And if you think this title wasn't thought of to maximise clickthroughs (again, regardless of the content of the article as clickbait ONLY applies to the title) ... you are very naive..
Other titles could be, getting rid of excess heat via infrared into space. Which would be less interesting to majority of people, as people read it, and think 'oh airconditioning, i got that... oh a new unit that beams into space ... neato...'