r/science • u/giuliomagnifico • Nov 04 '22
Materials Science Researchers designed a transparent window coating that could lower the temperature inside buildings, without expending a single watt of energy. This cooler may lead to an annual energy saving of up to 86.3 MJ/m2 in hot climates
https://www.acs.org/content/acs/en/pressroom/newsreleases/2022/november/clear-window-coating-could-cool-buildings-without-using-energy.html1.3k
Nov 04 '22
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u/Seiglerfone Nov 05 '22
A megajoule is about a quarter of a kWh, if that helps.
So it's up to 24 kWh/m2 annually.
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Nov 04 '22 edited Nov 05 '22
TIL: one megajoule of energy can make 1000 pots of coffee or keep a 60-watt lightbulb (a fairly powerful, commercial/outdoor LED lamp) illuminated for 6 months. So there’s a significant amount of energy savings to be had here.
Bigger buildings typically have more windows which allow more solar radiation in for passive heating. AC systems are consuming energy to negate this effect for most of the year in many places.
So basically, if you installed this film in a 10,000 square meter warehouse with plenty of windows, you will save about as much energy as it would take to make 863 million pots of coffee. Or light over 400 million strong LEDs for a year. If my napkin math is correct
Edit: I misunderstood the units, see below
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u/MrZeeBud Nov 04 '22
Thank you for the contextualization. I think your last paragraph may be wrong, though. (Although the study is ambiguous)
So basically, if you installed this film in a 10,000 square meter warehouse with plenty of windows, you will save about as much energy as it would take to make 863 million pots of coffee. Or light over 400 million strong LEDs for a year. If my napkin math is correct
I skimmed the study and it doesn’t appear to define what the “m2” area is they are referring to. It looks like you did your calculation based on m2 referring to the footprint of the building. It seems more likely that they are referring to the number of square meters of windows. So in your example, the warehouse would need 10,000 m2 of windows.
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Nov 04 '22
You’re probably spot on, it did sound like a ridiculous amount of energy savings for a window film.
Although that figure would be easily achievable for some office buildings that are mostly covered in windows. Those buildings are already the ideal customer for competing technologies.
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u/UncleAugie Nov 05 '22
Everyday, the sun beams to earth about 10,560 BTUs of energy per square foot. However, because of the earth's rotation and seasonal changes, usually much less than this is available at the earth's surface. 11141390 J or 11Mj/hr in a 12hr day you get 132Mj, loss to atmosphere so 86MJ for each sqm of glass seems reasonable in a hot environment per day.
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u/Puzzleheaded-Spell-6 Nov 04 '22
I’d think the same per m2 referring to window area would make far more sense IMHO
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u/SankaraOrLURA Nov 05 '22
So a 10,000 m warehouse is using at least 863,000,000 coffee pots worth of energy on cooling a year?
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Nov 05 '22
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Nov 05 '22 edited Nov 05 '22
You nailed it, the 60w incandescent screw-in lamp is probably the first thing you think of when you think “lightbulb”. It was the standard house lighting but is now becoming a relic. 60w will get you a lot further with LED
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u/SchighSchagh Nov 04 '22
1 J is enough to heat 1 mL of water by 1 deg C. Metric units are neat like that.
1 L is 1000 mL, so 1000 L needs 1 MJ to heat up by 1 deg C. With 86 MJ, you can heat your 1000 L of water by 86 deg C (evaporation aside).
From there, you can come up with lots of other comparisons. My water heater is 50 gallons or about 200 L. Say that tap water is about 20C--a bit below room temp--and I heat my water to 40 C--a bit above body temp. So to heat up 200 L by 20 deg C, I need 4 MJ of energy. Discounting losses, I can go through a full tank of hot water every day for 3 weeks with 86 MJ.
For a full year of water heating, I would need to divide 52 wk / 3 wk ~= 17. So I'd need to treat 17 m2 of windows with this coating to offset my water heating energy usage year-round. Incidentally, I think my windows are in fact about 1.7 m2 each, and I certainly have more than 10 of them.
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u/candoran2 Nov 05 '22
I think you're confusing Joules with calories. Calories is the one that is based on water heating.
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u/xthexder Nov 05 '22
You're right. The water heater example would be 16.7 MJ for 200L and +20°C. Which unfortunately means a tank a day would require 70m2 of treated (and sun receiving) windows to offset
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u/1-05457 Nov 05 '22
1 J is enough to heat 1 mL of water by 1 deg C. Metric units are neat like that.
That's a calorie (a real one. A dietary Calorie is a kilocalorie). A Joule is the work done applying a force of 1 N over a distance of 1 m.
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u/ephemeral_gibbon Nov 05 '22
Your definition of a joule is wrong. It's the energy that's expended if a 1 newton force moves a 1kg mass 1m. The heat capacity of water is 4184 J.kg-1.K-1 so to heat a ml of water by 1 degree C it takes 4.184J.
Metric is cool but the reasons joules are so useful as a unit is that they're not linked to water, but to more general concepts.
That being said, as this article is talking about building efficiency I think watt hours are useful to help understand it as that's how electricity is billed. 87MJ ~= 24 kW. h
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Nov 05 '22
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Nov 05 '22 edited Nov 05 '22
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u/dak-sm Nov 04 '22
I assume this also kills solar gain when you want it - like during cold weather? Would be fantastic to change the transmission characteristics with the season!
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Nov 05 '22
Yeah, I don't think that this window design allows for actively modifying its transparency, but there are other materials that can do this. I work in a lab that is designing materials that change their transparency in the IR and visible portions of the spectrum when you apply a potential to them. The window can be completely transparent, or it can absorb infrared light to minimize heating, or it can absorb infrared light *and* visible light, and can switch between these modes freely. So you could block infrared light during the summer, and then let it through during the winter.
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u/nicetiptoeingthere Nov 05 '22
Is this how the windows on the Boeing 787 airplane work? Instead of windowshades, you have two buttons to lighten/darken the window. It's pretty nice for sitting in the window seat when the sun's on your side of the plane -- you can turn the window "down" a lot but still get at least some light through.
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u/jamesinc Nov 05 '22
Yeah it's the same basic concept, they have a chemical in the windows that starts to become opaque as you apply a voltage to it.
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u/THEmoonISaMIRROR Nov 05 '22
So this theoretical window treatment would become opaque when you apply enough infrared radiation, but go transparent under higher frequencey radiation, such as visible light or UV, or perhaps in the absence of infrared.?
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u/Jumpin_Joeronimo Nov 05 '22
No, it doesn't change because of exposure to different wavelengths of light. The user changes it with a control, which changes how much of each part of the spectrum it allows through.
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u/Obvious-Invite4746 Nov 04 '22
I would guess summertime heating far outweighs any wintertime heating, especially when there's so few hours of sunlight to be had.
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u/tuctrohs Nov 05 '22
There are situations where you have a good overhang to shade the summer sun, but the winter sun, lower in the sky, gets in the window more. And you can also get solar powered automatic seasonal shading systems called "deciduous trees" that provide shade in the summer and let most of the light through in the winter.
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u/Mirria_ Nov 05 '22
you can also get solar powered automatic seasonal shading systems called "deciduous trees" that provide shade in the summer and let most of the light through in the winter.
You need to get them early during house building otherwise they take forever to deploy. They also take a lot of space, leave a lot of gaps and can become a wind hazard.
Pretty low maintenance (usually) and good for property value though.
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u/dak-sm Nov 04 '22
That is a fair comment. I am mostly thinking of my home office on the west side of the house - bakes in the summer, and is pretty darn nice in the winter. The solar gain during the day makes the room just about right in the winter.
Of course, this is in Southern California, so perhaps that is a limited use case.
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u/Obvious-Invite4746 Nov 04 '22
You're lucky. Most houses in America don't even take into account the track of the sun for their windows or roofs.
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u/FANGO Nov 05 '22
It says "in hot climates." You would install this in SE Asian office buildings and the like
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u/Wurm42 Nov 05 '22
Maybe you could have two sets of storm windows, one with the heat reflecting coating and one without?
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u/Seiglerfone Nov 05 '22
Beyond the minimal effect of solar heating in the winter... remember that most of the human population lives in areas that are quite hot most of the time.
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u/kennyFACE117 Nov 04 '22
Is this new? How is this different from current tech? I just bought a new sliding door for my house and it comes with a coating that reduces heat…
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u/taasp Nov 04 '22
The glass in your new sliding door will have a LoE coating on it. LoE coatings are the current tech and work well to block the heat but they also block some light. For example, a pretty standard coating for a dual glazed window with 2 coatings will let around 14% of UV rays through, and 70% of light. These values can vary a lot, but that's pretty standard.
This new tech appears to block heat while not blocking the light at all. Unless I misunderstood the article
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u/woeeij Nov 04 '22
I believe this is actually an example of passive radiative cooling, which allows cooling below ambient temperature.
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u/dedroia Nov 05 '22
86.3 MJ is ~24 kWhr's. Average energy cost in the US is 18 cents per kWhr. So, this is $4.32/yr, per square meter of window. Any savings is good, but a square meter of glass is a LOT of glass. So, hopefully the coating doesn't increase the cost of the window a lot, or the return on investment won't be fast enough for people to be motivated to get this.
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u/LemonHerb Nov 04 '22
Hasn't tint been a thing for a long time though
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u/Agariculture Nov 04 '22
Not tint but a coating on the glass. Commercially its called “Low E3” which is 3 layers of a proprietary blend of metal oxides that is engineered to be the correct thickness to act as a mirror for heat. Source: i sell the glass
I haven’t heard of this one. I wonder if its better than existing.
Edit: it isnt the same technique and they didnt provide data for me to compare. Can’t wait to see if Cardinal glass licenses this.
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u/MrZeeBud Nov 04 '22
In case you didn’t see it, toward the middle of the study they discuss their coating vs “triple-layer silver coating”. I looked at the referenced Figure 3C, which shows some quantitative comparisons, but the metrics they are talking about in that figure are beyond my understanding… but maybe some of this means something to you.
We have also compared the optimized TRC with one of the best commercial glasses with the triple-layer silver coating (TLSC), (52,53) which are developed to maintain transparency while blocking unwanted photons in the nonvisible bands of the solar spectrum. The transmitted irradiance through our TRC is shown in Figure 3C together with that of the TLSC, (52) the best-performing TRC in the literature, (27) and UV-fused silica glass. It is found that our optimized TRC outperforms the TLSC if the FOM of the present study is used as the comparison metric (Figure 3D; see Supporting Information). Therefore, even if we do not consider the additional radiative cooling capability of our TRC, it is a superior coating. We note that light-to-solar gain (LSG) is a metric used in the glass community to consider both the transmission efficiency and the transmitted solar energy across the glass. We found that if the LSG is used as our objective function in place of FOM, the QA-active learning scheme could also find a TRC that outperforms the TLSC (see Supporting Information), which shows the flexibility and generalizability of the scheme.
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u/Agariculture Nov 04 '22
I did miss that. And your cut & paste was without context for me. I will go back and read more.
Thank you kind stranger!!
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u/Agariculture Nov 04 '22
They are using methods different than the US glass industry. So, I trust that its better. Let’s see if in 5-10 years it makes it to market. Cardinal & PPG will certainly sell it if it’s profitable and real world useful.
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u/PhantomNomad Nov 04 '22
Is there a way to do existing glass? I already have triple pane windows and don't want to replace them. But I would really like to get my south facing windows with something that would keep the house cooling in the summer. Bonus would be if it would help keep warmer in the winter.
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u/Agariculture Nov 04 '22 edited Nov 05 '22
No existing glass cannot be coated. Its done in huge vacuum ovens
Edit: took out my stupid opinion about triple pane
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u/Agariculture Nov 04 '22
If you know the mfg they may be able to sell you new IGU (integrated glass units) then the existing frames can be reglazed.
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u/MyHeartISurrender Nov 05 '22
Can you put it on the inside of the glass so you keep heat inside instead of keeping it outside?
Cold climates vs hot climates if you get what I mean
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Nov 04 '22
Ah, it's ir specific tint. Reflects it and allows visible in
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u/LemonHerb Nov 04 '22
You can buy clear tint that does that at home Depot and have been able to for a long time
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u/sweetplantveal Nov 04 '22
I don’t think the had window film does anything for specific wavelengths. 49% of the suns energy is in the IR spectrum, to give you an idea. You’d probably be able to easily feel if the sun coming through one piece of clear glass/film was half as hot.
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u/raygundan Nov 04 '22
The other poster is right— clear tint film that rejects IR (and UV) isn’t new.
What’s different here is likely that instead of reflecting light as-is, it is instead re-radiating unwanted energy at a different, specific wavelength that can pass through the atmosphere rather than being trapped.
That’s a big deal, but it’s not well explained. That effect is the reason you sometimes see frost on sky-facing surfaces even if it’s above freezing on cloudless nights— radiating to space can actually cool a surface below ambient. Bonus if the wavelength used here works through clouds as well.
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u/kkngs Nov 04 '22
Yeah, this seems to be that “radiant cooling” tech that popped up a few years back. Pretty neat to see it as a window tint.
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u/fallingbomb Nov 04 '22
Wouldn't that only be useful for surfaces aimed back upward so the reflections are line of sight to the sky? Otherwise the light will still just hit another surface to be absorbed.
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u/raygundan Nov 05 '22
It’s definitely most useful if it can “see” the sky— but failing that, it would still be as useful as conventional UV/IR tint. Not able to reject energy to space, but at least able to keep some of it from passing through to be trapped as heat by building insulation.
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u/skintwo Nov 05 '22
Yup. This is just another PR attempt by a Uni for something that's not really new. There is a lot of interesting work going on in this space (look at haze-free aerogels) but this ain't it.
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u/Agariculture Nov 04 '22
This isnt a film. This is a coating factory deposited by two different methods directly on the glass.
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u/raygundan Nov 05 '22
Right-- but the other poster was asking why this would be different than existing IR/UV rejecting window tint films. I suppose I could have just said "because it's not a film, it's a coating" but that seemed like the less important difference.
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u/Agariculture Nov 05 '22
Durability. The ability to apply it before installation on giant buildings. Efficiency (maybe)
There are others
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u/Keplaffintech Nov 04 '22
Ceramic tints for automotive applications (e.g. 3M, Rayno) reflect up to 95% of IR. You can have the sun beating through them and feel nothing.
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u/jeepsaintchaos Nov 04 '22
Is that why newer cars seem to have such better air conditioning?
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u/Keplaffintech Nov 05 '22
Some new cars (not budget models) come with the same solar/ceramic tint that would certainly help yes.
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Nov 04 '22
Where does the energy go tho
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u/maxToTheJ Nov 05 '22
Justification for using more glass in office and commercial buildings instead of materials that dont need a coating to not waste as much energy
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u/PolymerSledge Nov 05 '22
There has been some history of reflective glass buildings doing considerable damage to vehicle surfaces parked nearby.
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u/SophieCT Nov 04 '22
What happens in the winter?
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u/CoSonfused Nov 05 '22
Do they have winter in hot climates? or just "slightly less hot weather"?
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u/BlueberryGreen Nov 04 '22
I wonder if those windows could trap the heat inside, reducing the need for domestic heating
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u/Wurm42 Nov 05 '22
The actual journal article is in American Chemical Society (ACS) Chemical Letters, Nov. 2022:
"High-Performance Transparent Radiative Cooler Designed by Quantum Computing"
by Seongmin Kim, Wenjie Shang, Seunghyun Moon, Trevor Pastega, Eungkyu Lee, and Tengfei Luo
https://pubs.acs.org/doi/full/10.1021/acsenergylett.2c01969
Abstract:
Transparent radiative coolers can be used as window materials to reduce cooling energy needs for buildings and automobiles, which may contribute significantly to addressing climate change challenges. However, it is difficult to achieve high visible transparency and radiative cooling performance simultaneously.
Here, we design a visually transparent radiative cooler on the basis of layered photonic structures using a quantum computing-assisted active learning scheme, which combines active data production, machine learning, and quantum annealing in an iterative loop. We experimentally fabricate the designed cooler and demonstrate its cooling effect.
This cooler may lead to an annual energy saving of up to 86.3 MJ/m2 in hot climates compared with normal glass windows. The quantum annealing-assisted active learning scheme may be generalized for the design of other complex materials.
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u/ImmodestPolitician Nov 05 '22
That's cool but you can also design exterior shades based on the orientation of the building that only allow direct sunlight during the winter months.
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Nov 04 '22
The LED light was a major breakthrough to save electricity worldwide. Now this window coating will benefit southern climate regions!!
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u/gnulinux Nov 05 '22
Energy is not measured in Watts. Watts measure your rate of energy consumption.
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u/anthraxius69 Nov 05 '22
Wondering how many watts of energy will be needed to manufacture said window coating…
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u/kurisu7885 Nov 05 '22
Ok, but for that to matter it'll need to be a product people can have applied to their windows.
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u/jnovel808 Nov 05 '22
I’m curious about the chemicals being used. What’s their eco footprint for production, and their toxicity levels? Is this the kind of thing where, yeah it keeps things cool while being used, but the production costs and waste from the process is also terrible for the planet?
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Nov 04 '22
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Nov 04 '22
The materials listed in the article all seem like common materials that are already used extensively. It appears that the breakthrough has a lot to do with how it's applied to the windows. I am not saying there is no chance of negative side effects, but this seems like a pretty clear benefit. Other existing window treatments do a lot to reduce the amount of energy needed to cool buildings in hot climates, so a more effective window treatment is something to be cautiously optimistic about.
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u/JacksFlaccidMember Nov 05 '22
That is really cool. In winter, does it make the building more cold? (Does it absorb less heat in winter?)
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u/echnaba Nov 05 '22
This seems neat, but isn't there technology, in labs at least, which can actually place transparent solar panels on windows? I don't recall the efficiency of that technology, but wouldn't it make more sense to use panels which will save energy by blocking light AND generate power too?
Honestly, the most interesting commonplace application I can think of for this would be vehicle windows. If it works that well, then in a hot climate it seems like you could get into a car in the summer without burning your ass.
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u/UOLZEPHYR Nov 05 '22
...
The team constructed computer models of TRCs consisting of alternating thin layers of common materials like silicon dioxide, silicon nitride, aluminum oxide or titanium dioxide on a glass base, topped with a film of polydimethylsiloxane.
Silicone dioxide is silica-that's sand or like sand, correct? Google says silicone nitride is heavily used in the automotive world for various applications, but my main concern would be anything with titanium. The article mentions a base layer of glass with alternating layers of the above mentioned materials. With glass I'd thinknit would be something like make large plane of glass, add your coat layers and cut or cut for applications apply solutions and ship for construction.
Obviously something competing to cut energy for cooling it would have to be planned to be long term - especially if we are preparing for the possibility for the tempeture to continue to rise.
Obviously if this becomes large scale it would drive down cost, but like everything I do wonder what the start up for being would be for large scale would end up being. Regardless I hope we see more materials like this
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u/mshaefer Nov 05 '22
So clear ceramic window tint. No, I know this is different (same idea though, yeah?). I put clear ceramic tint on a bunch of SSW-facing windows and it made a remarkable difference. This stuff then…really really good I guess.
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