Scientists Reveal Roof Coating That Can Reduce Surface Temperatures Up To 6C On Hot Days (theguardian.com) 52
An anonymous reader quotes a report from the Guardian: Australian scientists have developed roof coatings that can passively cool surfaces up to 6C below ambient temperature, as well as extract water from the atmosphere, which they say could reduce indoor temperatures during extreme heat events. One coating made from a porous film, which can be painted on to existing roofs, works by reflecting 96% of incoming solar radiation, rather than absorbing the sun's energy. It also has a high thermal emittance, meaning it effectively dissipates heat to outer space when the sky is clear. Its properties are known as passive radiative cooling. [...]
In a study, published in the journal Advanced Functional Materials, the researchers tested a prototype for six months on the roof of the Sydney Nanoscience Hub, pairing the cool paint with a UV-resistant topcoat that encouraged dew droplets to roll down into a receptacle. As much as 390 milliliters per sq meter per day could be collected for about a third of the year, the scientists found. Based on that water capture rate, an average Australian roof -- about 200 sq meters -- could provide up to 70 liters on days favorable for collecting dew, they estimate. [...]
In well-insulated buildings, a 6C decrease in roof temperature "might result in a smaller fraction of that cooling being reflected in the top level of the house," [said the study's lead author, Prof Chiara Neto of the University of Sydney], but greater temperature reductions would be expected in most Australian houses, "where insulation is quite poor." She said the coating could also help reduce the urban heat island effect, in which hard surfaces absorb more heat than natural surfaces, resulting in urban centers being 1C to 13C warmer than rural areas. The researchers found that the prototype coating was comprised of poly(vinylidene fluoride-co-hexafluoropropene), which is used in the building industry but was "not a scalable technology going forward" due to its environmental issues. However, they are now commercializing a water-based paint with similar performance that is affordable and environmentally safer, costing about the same as standard premium paints.
In a study, published in the journal Advanced Functional Materials, the researchers tested a prototype for six months on the roof of the Sydney Nanoscience Hub, pairing the cool paint with a UV-resistant topcoat that encouraged dew droplets to roll down into a receptacle. As much as 390 milliliters per sq meter per day could be collected for about a third of the year, the scientists found. Based on that water capture rate, an average Australian roof -- about 200 sq meters -- could provide up to 70 liters on days favorable for collecting dew, they estimate. [...]
In well-insulated buildings, a 6C decrease in roof temperature "might result in a smaller fraction of that cooling being reflected in the top level of the house," [said the study's lead author, Prof Chiara Neto of the University of Sydney], but greater temperature reductions would be expected in most Australian houses, "where insulation is quite poor." She said the coating could also help reduce the urban heat island effect, in which hard surfaces absorb more heat than natural surfaces, resulting in urban centers being 1C to 13C warmer than rural areas. The researchers found that the prototype coating was comprised of poly(vinylidene fluoride-co-hexafluoropropene), which is used in the building industry but was "not a scalable technology going forward" due to its environmental issues. However, they are now commercializing a water-based paint with similar performance that is affordable and environmentally safer, costing about the same as standard premium paints.
Does it also make julian fries? (Score:3)
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Speaking of solar, it seems like it would make more sense to cover as much of the roof as possible with it. Use reflection where you can't install PV or water heating.
If it's cheap and durable enough, maybe it could be used with solar as a reflector.
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If I could snap my fingers and get rooftop solar I would, but I think, what if some of all those new holes in my roof were to leak? And my roof is 20 years old, I guess you have to un-do all the solar to replace the shingles?
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Given the mention of (presumably) asphalt shingles I assume you're in the US? Good-quality solar panels here (without a tariff premium) are so cheap that the dominant cost is labour for the install, not the panels. In particular if you do the install yourself it's pretty much a no-brainer to plaster your roof with panels because the incremental cost/effort to install 5 vs installing 20 is minimal.
The price for whatever the magic paint in TFA is isn't given but I doubt it'll be cheap, which means it could
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The Man in the White Suit (Score:2)
More details omitted by The Guradian -
The company created to commercialize the technology [dewpointinnov.com]
Press Release from the University of Sydney [sydney.edu.au]
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Removable for the winter? (Score:4, Insightful)
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Right, that's the problem. I believe it takes more energy to heat a house from 30 to 70 degrees in the winter than it does to cool one from 85 to 70 in the summer. Obviously there are more variables at play.
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its australia, it doesn't get that cold.
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Winter is rarely less than 0 (32F), more often around the 8-10 mark (50F). A lot of money is spent on cooling. Maybe more than northern hemisphere countries.
Yes, there is some money spent in winter, but insolation is much lower then too, enough to be close to negligable, a little loss from the insolation in Winter isn't going
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Right, that's the problem. I believe it takes more energy to heat a house from 30 to 70 degrees in the winter than it does to cool one from 85 to 70 in the summer. Obviously there are more variables at play.
For those very numbers you're right, now do those numbers apply everywhere, or just where you live? I know plenty of places that put a LOT of energy into cooling and yet have zero heating function. On the flip side where I live we only have heating and no cooling. But in any case heat reflective coatings work both ways. Fundamentally it doesn't just take energy to change a temperature, it takes energy to compensate for the energy lost. It doesn't say here that this coating works only one direction.
Re: Removable for the winter? (Score:3)
You don't like heat in the summer, why use it in the winter. I'm sure you can sell the ice from all the condensation to offset the costs. You should probably disclose it will cause some form of awfulness in 20 years time what we weren't aware of today.
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Am I going to pay way more to heat my house in the winter?
Maybe? Do you heat your house in the winter? Many people in the world don't. Just like I don't cool mine in the summer. If you're in an area of wildly swinging summer to winter temperatures then this probably is not a good solution for you, that doesn't mean it isn't an amazing breakthrough for a LOT of people.
Okay that was the obvious one dimensional answer, the more complex answer is that radiative control goes both ways. Take for example a typical modern triple glaze window, it contains two IR reflective
Prior Art (Score:5, Funny)
"White paint"
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slate grey colourbond is very popular these days. massive heat island effects in new developments.
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"White paint"
White paint isn't good enough to cause passive cooling. Hell, not all white paint is white in the infrared. Getting something that's emissive too is even harder. All this is pretty much mentioned in the summary. Next time read it before being snarky.
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Fair enough, fancy white paint.
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A word of warning about "roof paint" (Score:5, Informative)
A word of warning about roof paint.
Years ago Florida Power and Light (FPL) offered rebates and encouraged people to paint their roofs white to reflect sunlight and lower bills. Many gullible people took the bait.
Then the problems started. The paint would shrink, damaging the roof, letting water in. it was a disaster. Even tile roofs were affected. Water leaks. Disaster. Ruined houses. Lawsuits.
I'd be very leery about doing any such thing to a house. Maybe if the material is engineered from birth to be reflective, but as a coating? Fuck that.
There's always someone (or large groups of someones) trying to gyp people using "The Environment" as bait.
https://www.palmbeachpost.com/... [palmbeachpost.com]
Re:A word of warning about "roof paint" (Score:4, Informative)
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We had to have our entire roof reshingled after a particularly bad storm.
It turns out that of the various colors, the lightest (or 2?) was actually energy star rated. So we took it.
It turned out to be worth about 2F inside as compared to the prior black shingles.
We got another 2F when we replaced the swamp cooler--the newer model had an 18" pad instead of 12".
Between the roof and the bigger pads, we only had a single non-monsoon season day where we had to switch over to AC this summer--in Las Vegas!
(I'm go
Re:A word of warning about "roof paint" (Score:5, Informative)
For those of you confused about how a thin coating of paint could possible damage shingles, it wasn't standard paint. It was a stretchy elastometric paint that's specifically banned by the state's building codes for use on asphalt roofs. It damages them in multiple ways. First when the paint shrinks it's apparently strong enough to cup/curl the shingles. Second, when water gets under the paint it becomes trapped and rusts away the roofing nails far, far faster than normal.
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There are rubberized coatings with aluminum in them which don't shrink and are fine on a roof. I would imagine the coating would go on something like this rather than on shingles
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They make metal roof "shingles". Basically huge pieces of sheet metal. Maybe not good for hurricane country, but you can get white metallic reflective paint for metal - we call it "automotive paint".
Metal roofs have the slight disadvantage of being loud in a hail or heavy rainstorm, but that's what insulation is for. They also serve as a good base for solar panels.
As a bonus, they last twice as long as shingles. They cost more though.
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try using mirrors. What could go wrong? :)
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You're post is daft and one sided. Many people all over the world have painted roofs. Your situation applies to one type of coating on one type of roof (and one that is almost uniquely American at that). I've never lived in a roof that wasn't painted. In fact we've often re-coated our roofs over the years. But then we also don't make them out of left over oil industry crud, like those bitumen shingles I'm still amazed are used.
oh I've heard of that (Score:2)
it's called WHITE PAINT
it's an incredible new innovation, you should try it!
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It's not just white paint. Being highly reflective is only 1/2 the equation. There are certain materials with extremely high IR emmissivity which will actively cool the structure they are applied to. Not only that, but it must be a frequency of IR that the atmosphere is transparent to. Whether such coatings are ready for widespread use is up in the air.
This guy has several videos about trying to homebrew such a coating Making Infrared Cooling Paint From Grocery Store Items (w/Novel CaCO Microsphere Syn [youtube.com]
Re: oh I've heard of that (Score:2)
Sorry, FANCY white paint
Sounds great but.... (Score:1)
boat (Score:2)
6C is ok but not amazing (Score:3)
Worth bearing in mind that solar panels reduce roof temperatures by 20C+, and cause materially larger drops in heat flow into the building and HVAC use.
Obviously, the paint can cover the whole of a building's roof, and potentially its entire surface, while solar only covers a portion.
And I'm all for both-and. But it's important to understand that this 6C is helpful but not earth shattering
Metal Roofing (Score:4, Informative)
Years ago I owned a highly renovated one room brick schoolhouse (ground-source geothermal heat pump, radiant floor heating, two stories). The attic was cooled with a power vent (at some temp (I think it was like 115f) a central fan would come on and push hot air through a single top vent and pull it up through the eves). In the summer almost every afternoon when it was sunny you could hear the power vent come on.
About 10 years into ownership I installed a metal roof [edcoproducts.com] with a slate-like look. The company claimed that the roof would make the schoolhouse more energy efficient by reflecting a lot of the incoming solar heat. Well, the power vent *never* came on again in the 3 years after I installed the roof. At one point I even checked to make sure it was still working. In fact the A/C would only come on maybe a couple of times per summer instead of almost every day.
The install cost was about double what shingles would be, but next time I have to install a roof I'm doing the same thing. These things have a lifetime non-prorated warranty unlike shingles which are prorated. I don't have the house anymore and I'm not affiliated with the company in any way.
So,... (Score:2)
So, in other words, um, paint the roof white.
So if I make the shape of a parabolic reflector (Score:2)
It's called white paint! (Score:2)
Existing product reduces by 22.2222C (Score:2)
Unfortunately, because of <insert cause of everything in the United States being more expensive>, the paint price went up more than 2x for a 5-gallon bucket.
Something similar exists (Score:2)
A friend of mine has a backyard astronomical observatory.
In the Great Lakes weather, it is challenging to keep the equipment inside safe year-round from humidity and condensation. Summers are hot and humid.
Other friends have an A/C that they keep running, so there is no condensation, and no mold on optics, and rust on electronics.
This friend though, does not use an A/C at all.
Instead he covered the observatory's roof with something that commercial building use to safe energy. It reflects all the incident In