Ultrawhite BaSO4 Paints and Films for Daytime Radiative Cooling
pubs.acs.org
pubs.acs.org
It seems almost cheating to simply change their reflectivity for a huge cooling power savings.
In NYC we use black tar to seal the roof, but then it is painted silver or white. You almost never see an actual black or dark colored roof.
Most white paints used nowadays contain titanium white.
Nevertheless, many white plastics contain other white pigments instead of titanium white. Titanium white itself is inert, but when it is exposed to the sun light it can catalyze the destruction of organic substances like plastics or paint binders that have not been selected to be resistant to this.
So when using titanium white outdoors, the white paint must be specified as UV resistant.
I have not heard about paper that uses titanium white.
That might be due to the higher cost of titanium white, which might be too much compared to the cost of paper.
The barium that might have leached will be precipitated by the carbon dioxide from the air into barium carbonate.
Any form of soluble barium left in the environment will end soon as either barium sulfate or barium carbonate, which are insoluble, thus non-poisonous.
Barium is one of the least dangerous metals with high atomic number. You have to do something really stupid and deliberate with it in order to be able to poison anyone.
15 years ago I put a white, metal roof on my house, my summer cooling costs are half or less my neighbors' with the shingled roofs, and they've replaced their shingles in that time frame.
The crop duster aircraft also use my house as a navigation marker and we get to see them frequently.
I'm struggling with the same decision right now. I have a small (2k sqft is small in this area) 300k structure and I don't know whether it will be worth lot value in 10-15 years or still worth 300k+inflation+value additions. The surrounding neighborhood with 1-2million dollar structures says "lot value" even if it's pristinely maintained.
It is one of those upgrades you can add to a house that actually retains its value when you go to resell... Most metal roofs have lifespans that are minimum double that of shingles and, per your example, solar panels.
Of course, most people buying in the countryside aren't intending on moving out in fewer than 6 years; 7 minimum is generally considered the break even point around here.
It sounds like your area is one where the location and the market determine value far more than anything on the land, so treat it as "build to suit" commercial property and assume anything built on it is disposable.
Shingles are almost always more expensive because of laborious installation.
Its nowhere near as loud as an aluminum skinned mobile home.
The other side is that having a roof which warms itself in winter is better for reducing snow accumulation. Though that’s also less of a consideration for a slippery metal roof.
Plus, in practice, you'll want a ton of insulation between the interior space and the roof anyway. So if you've done a good job there it's kind of a moot point wrt/interior comfort. But sending that power back into space rather than absorbing it can reduce thermal cycle stress on the roof and keep the outdoor space nearby cooler.
So much wrong here. Asphalt shingles neither "retain heat" nor "warm themselves." You really do not want either property in a roof covering in a climate where it snows because that will cause the formation of ice dams. If you have snow on your roof, it obviously covers the black shingles - now you have a white roof anyway. If it is winter and you do not have snow on your roof, it is still not worth it - solar irradiance at 50° latitude (approximately Timmins, Ontario) is going to be about a factor of 7 less in January than in June. You are much better off with a white roof in northern Canada to reduce peak heat stress in the summer, which will continue to get worse and worse due to greenhouse gasses.
We had a steep roof in the Okanagan which rose about 20ft to the peak. That extra room was problematic in winter for heating but a life saver in the hot, sunny summer. The loft was unbearable during the summer.
A neighbor with a low roof would run a sprinkler on his roof all summer long, that's how bad the heat would get.
My previous house already had a light colored metal roof, and my current one is shingles that are not due to be replaced for another ten years or so, but these are good things to think on.
Not just black. Dark, fractulate, nigh-furry extremely light-absorbing black.
It's like they designed it to soak up sun and get hot. So hot that it starts to melt. So hot that you need to use special nails so they don't pull through the half-melted black goo.
Anything would be an improvement.
I like white painted steel.
Residential buildings usually have sloped roofs visible from the ground so the roof color is an architectural choice. Depending on the locale, current building codes can require enough roof insulation that very little heat flows through the roof in either direction. The insulation has an added benefit of preventing heat loss in the winter.
...in the USA.
In many (most?) other countries pure ethanol can be bought easily over the counter, and where I live even at any gas station. Yes, you could drink the ethanol from the gas station here (it has no additives, but better dilute it first), but nobody does because the cheapest cachaça isn't any more expensive.
You can get pure, food grade ethanol at the pharmacy.
You can buy it, but it'll be taxed like drinking alcohol.
However, I'm surprised that other alcohols (e.g. isopropanol) that don't suffer from this cannot be used instead of ethanol.
I only read the abstract, but it seems like they’ve considered your stated limitations.
“we experimentally demonstrate remarkable full-daytime subambient cooling performance with both BaSO4 nanoparticle films and BaSO4 nanocomposite paints”
“providing great reliability, convenient paint form, ease of use, and compatibility with the commercial paint fabrication process.”
Also, you can always get commercial licenses for restricted substances like ethanol; that’s not an actual problem for house paint jobs.
Only ethanol needs to be denatured. You can easily get 99.953% pure isopropyl on Amazon, and it isn't poisoned because isopropanol is already poison.
Select quotes:
> Overall, the BaSO4 film reached a solar reflectance of 97.6% and an emissivity of 0.96 in the sky window (Figure 2b). Its solar reflectance is significantly higher than that of the commercial white paint (400 μm thickness), especially in the UV and NIR ranges. [...] For the BaSO4 paint, a standalone paint sample of 400 μm reached similar optical properties (98.1% solar reflectance, 0.95 sky window emissivity)
> To demonstrate the reliability of our BaSO4 paint, we conducted abrasion test, outdoor weathering, and viscosity characterizations. [...] The BaSO4 paint reached a wear index of 150, comparable to the commercial exterior paint with a wear index of 104. The weathering test was conducted by exposing the BaSO4 paint outdoors for 3 weeks (Figure 4b). The solar reflectance remained the same within the experimental uncertainty.
I cringe every time a HN comment starts with “this is nothing new; not ground breaking; people should’ve expected this”.
So much for a discussion forum where you’re meant to read the post and spark insightful commentary.
Actually, its because ethanol is a aziotroph with water at about 95%. To distill it further, you need to add dangerous and toxic organic compounds. 95% ethanol is the highest that is still safe to drink.
It's easiest to find at the hardware store as very thin tape for wrapping pipe threads, but I bought a few bars of it (about 5mm x 30mm x 300mm) on eBay years ago, so I know it comes in a form that would be more convenient for making into roofing or siding material. I don't know how it holds up to weather, though. According to that paper, it needs to be at least 0.5mm thick to reflect longer wavelengths, so anyone who's curious about testing it should find the thicker stuff like I did.
[1] https://www.researchgate.net/figure/Reflection-coefficient-f...
But for teflon to passively cool, it would have to be strongly absorbent in the IR.
The way it works is this: the sun’s rays are at 5500 K. So you pick the set of materials that reflect light in the visible gap (the atmosphere takes care of the rest).
This keeps the material from getting heat.
Then, from this set, you pick a material that is strongly absorbent in IR.
If it absorbs in IR, itll emit there too, there y cooling itself
The trick is to design a system where the total power absorbed across the solar irradiance spectrum is less than the power that is emitted in the sky window, so that the system is a net power sink (in this case to the tune of 100W per sq. meter or so).
It does very well. The main terminal of Denver International Airport has an enormous PTFE-coated fiberglass fabric roof. It's decades old now and has weathered hail, high winds, and Colorado sun without any significant wear that I know of.
EDIT:
The same product has since been used in a bunch of other stadiums and other large structures, including the Georgia Dome where it survived a near-miss by a tornado with only minor tears:
https://spinoff.nasa.gov/Spinoff2009/ip_2.html
> "The material is pound-for-pound stronger than steel while weighing less than 5 ounces per square foot. It offers up to 24 percent solar translucency while providing as much as 75 percent solar reflectance"
Black is both best radiator and best absorber. So it works perfectly in space (where you minimize incoming energy by turning it perpendicular to sun), and not so good on surface.
This material works by being reflective in spectrum, where most of sunlight energy is (which makes it white, as visible spectrum ~= sunlight on earth surface), and being 'black' (good radiator and absorber) in other spectra.