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Energy-saving coating without pigment keeps the surface beneath cool

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Re: Energy-saving coating without pigment keeps the surface beneath cool

#11

Post by londons_explore »

hammyhavoc wrote: post #10
londons_explore wrote: post #8

Paint coatings can make a massive difference to temperatures in a home. People understand "black paint = hot", but that isn't even necessarily true, and there is far more to it. I believe building regulations should require specific performance from paint on new buildings, and that commercial painters be required to replace any paint on a 'same or better' basis. Performance would be measured on the basis of watts of…

Tell us more.

When you put a hot thing near a cold thing, they exchange heat and the temperatures even out.

The heat moves via light - infrared light usually. Cooler things emit less light overall, and the light they do emit tends to have a longer wavelength (thats why the embers of a fire might glow red, but a hotter fire might be orange or yellow).

For each color of light that something might emit or absorb, there is a 'shinyness' (technically known as reflectance spectra). A shiny surface reflects light, which means it will take longer to heat up, or longer to cool down.

By making a material which is shiny in the redder (ie. longer) wavelengths, yet not shiny in the shorter wavelengths, you can make a material which heats up fast when put next to a very hot item (like the sun), but doesn't cool down fast when put next to a very cold object (like the night sky). That would make a great paint for a building in a cold climate! This would be a visually 'black' material to our eyes, although you could design it to be any human color if you trade some performance.

Likewise, one can do the reverse. Reflective of short wavelengths, and non-reflective of long wavelengths. That will help it stay cool in the sun, and lose as much heat as possible at night to the sky. The ideal material for this would be visually white, but again, you can trade a little performance for any other color.

It is also possible to have panels which physically flip to reveal another coating either between summer and winter, or between day and night to get even better results - although obviously with a complexity cost. Shutters in some european countries are an early version of this idea.

Note - the above is a simple explanation. For the full explanation, see [1]

[1]: https://en.wikipedia.org/wiki/Black-body_radiation

Re: Energy-saving coating without pigment keeps the surface beneath cool

#12

Post by HopenHeyHi »

slimsag wrote: post #5

Two YouTube researchers[0][1] (they make science content that is very much not in the traditional form of YouTube) have been working on Infrared Cooling Paint for almost a year now and have been detailing how individuals can make it at home (although a fairly involved/lengthy process today.) There's definitely something here, hopefully someone sells it pre-made, I'd love to try some. [0] https://www.youtube.com/watch…

These two, NightHawkInLight and TechIngredients are great and you should watch all their videos not just about this subject.

Re: Energy-saving coating without pigment keeps the surface beneath cool

#13

Post by stdbrouw »

londons_explore wrote: post #11
hammyhavoc wrote: post #10

Earlier quoted context omitted.

Tell us more.

When you put a hot thing near a cold thing, they exchange heat and the temperatures even out. The heat moves via light - infrared light usually. Cooler things emit less light overall, and the light they do emit tends to have a longer wavelength (thats why the embers of a fire might glow red, but a hotter fire might be orange or yellow). For each color of light that something might emit or absorb, there is a 'shinynes…

Can a coating on the outside of a material really have an appreciable impact on heat transfer from inside to outside, at night? I get that a coating can block or admit light or radiation coming from somewhere else, but surely if the material itself is hot then thermal conduction within the solid will make the coating itself hot, and shed heat, too? Wouldn't you need some sort of "heat shield" offset from the outer walls for your approach to work at night, if at all? Or if not, why are we still covering homes with big chunks of styrofoam, polyurethane and mineral wool?

Among architects, I'm seeing a lot more hype about high thermal mass, e.g. sand-lime bricks and woodfiber insulation, to design houses that respond very slowly to outside temperatures.

Re: Energy-saving coating without pigment keeps the surface beneath cool

#14

Post by aaron695 »

londons_explore wrote: post #8

Paint coatings can make a massive difference to temperatures in a home. People understand "black paint = hot", but that isn't even necessarily true, and there is far more to it. I believe building regulations should require specific performance from paint on new buildings, and that commercial painters be required to replace any paint on a 'same or better' basis. Performance would be measured on the basis of watts of…

> Performance would be measured on the basis of watts of absorption under sunlight, and watts of emissions to the night sky. It is possible to design paint that visually is any color, yet maximizes or minimizes each of those parameters independently

This doesn't exist.

Or is there a link to commercial paints that can do this? Or testing on real buildings not claims from a labs media department?

Here's a link disproving thermal paints which are ugly as well as don't work - https://www.sciencedirect.com/science/article/abs/pii/S03787...

Given money most people could better insulate their homes so even if these could exist they are pointless unless they are also reasonably priced.

Re: Energy-saving coating without pigment keeps the surface beneath cool

#15

Post by londons_explore »

stdbrouw wrote: post #13
londons_explore wrote: post #11

Earlier quoted context omitted.

When you put a hot thing near a cold thing, they exchange heat and the temperatures even out. The heat moves via light - infrared light usually. Cooler things emit less light overall, and the light they do emit tends to have a longer wavelength (thats why the embers of a fire might glow red, but a hotter fire might be orange or yellow). For each color of light that something might emit or absorb, there is a 'shinynes…

Can a coating on the outside of a material really have an appreciable impact on heat transfer from inside to outside, at night? I get that a coating can block or admit light or radiation coming from somewhere else, but surely if the material itself is hot then thermal conduction within the solid will make the coating itself hot, and shed heat, too? Wouldn't you need some sort of "heat shield" offset from the outer wa…

There are benefits to all these approaches, and combining them all gives best results.

But specifically on coatings, it's true that conduction and convection also play a role, and radiation is only part of the picture. However, it is theoretically possible to design a coating that can cool a material by 45C (~80F) compared to ambient at night, and practically a cooling of 4C (8F) has been achieved [1]. 4C is pretty substantial, considering it stacks on top of the effects of insulation, high thermal mass, and efficient heating/cooling appliances.

Remember that in the daytime the effect is far more substantial - the difference between the best and worst thermal coatings could easily be 100C - when people say 'that rock is so hot I could fry an egg on it', it's simply due to the absorption properties of the rock under sunlight.

[1]: https://www.mdpi.com/2079-6412/10/2/144

Re: Energy-saving coating without pigment keeps the surface beneath cool

#16

Post by shanebellone »

stdbrouw wrote: post #13
londons_explore wrote: post #11

Earlier quoted context omitted.

When you put a hot thing near a cold thing, they exchange heat and the temperatures even out. The heat moves via light - infrared light usually. Cooler things emit less light overall, and the light they do emit tends to have a longer wavelength (thats why the embers of a fire might glow red, but a hotter fire might be orange or yellow). For each color of light that something might emit or absorb, there is a 'shinynes…

Can a coating on the outside of a material really have an appreciable impact on heat transfer from inside to outside, at night? I get that a coating can block or admit light or radiation coming from somewhere else, but surely if the material itself is hot then thermal conduction within the solid will make the coating itself hot, and shed heat, too? Wouldn't you need some sort of "heat shield" offset from the outer wa…

"Wouldn't you need some sort of "heat shield" offset from the outer walls for your approach to work at night, if at all? "

It sounds like this paint is a "heat shield" that modifies the rate of thermal transfer.

Shouldn't that mechanism improve the performance of the existing substructure and insulation?

Re: Energy-saving coating without pigment keeps the surface beneath cool

#17

Post by londons_explore »

stdbrouw wrote: post #13
londons_explore wrote: post #11

Earlier quoted context omitted.

When you put a hot thing near a cold thing, they exchange heat and the temperatures even out. The heat moves via light - infrared light usually. Cooler things emit less light overall, and the light they do emit tends to have a longer wavelength (thats why the embers of a fire might glow red, but a hotter fire might be orange or yellow). For each color of light that something might emit or absorb, there is a 'shinynes…

Can a coating on the outside of a material really have an appreciable impact on heat transfer from inside to outside, at night? I get that a coating can block or admit light or radiation coming from somewhere else, but surely if the material itself is hot then thermal conduction within the solid will make the coating itself hot, and shed heat, too? Wouldn't you need some sort of "heat shield" offset from the outer wa…

> why are we still covering homes with big chunks of styrofoam

The energy loss through foam depends on the temperature on each side of it. So if you can use a fancy coating to keep the outside of your house cool/hot in the day/night, then the energy losses through the styrofoam are reduced, and eventually your heating/cooling bill is reduced.

Re: Energy-saving coating without pigment keeps the surface beneath cool

#18

Post by shanebellone »

londons_explore wrote: post #15
stdbrouw wrote: post #13

Earlier quoted context omitted.

Can a coating on the outside of a material really have an appreciable impact on heat transfer from inside to outside, at night? I get that a coating can block or admit light or radiation coming from somewhere else, but surely if the material itself is hot then thermal conduction within the solid will make the coating itself hot, and shed heat, too? Wouldn't you need some sort of "heat shield" offset from the outer wa…

There are benefits to all these approaches, and combining them all gives best results. But specifically on coatings, it's true that conduction and convection also play a role, and radiation is only part of the picture. However, it is theoretically possible to design a coating that can cool a material by 45C (~80F) compared to ambient at night, and practically a cooling of 4C (8F) has been achieved [1]. 4C is pretty s…

Are they attempting to generate electricity from these coatings yet?

Sounds like both the "keep warm" and "keep cold" coatings offer that possibility.

Re: Energy-saving coating without pigment keeps the surface beneath cool

#19

Post by mensetmanusman »

https://www.3m.com/3M/en_US/energy-conservation-us/applicati...

3M sells film that does this. Advantage for film over paint is that it doesn’t build up, as it can be removed, recycled, and replaced. This is especially important for things that move so as not to gain additional weight.

Very cool material to experience in person. It’s black body emission is also tuned to exit the atmospheric IR window.

Re: Energy-saving coating without pigment keeps the surface beneath cool

#20

Post by Bjartr »

aaron695 wrote: post #14
londons_explore wrote: post #8

Paint coatings can make a massive difference to temperatures in a home. People understand "black paint = hot", but that isn't even necessarily true, and there is far more to it. I believe building regulations should require specific performance from paint on new buildings, and that commercial painters be required to replace any paint on a 'same or better' basis. Performance would be measured on the basis of watts of…

> Performance would be measured on the basis of watts of absorption under sunlight, and watts of emissions to the night sky. It is possible to design paint that visually is any color, yet maximizes or minimizes each of those parameters independently This doesn't exist. Or is there a link to commercial paints that can do this? Or testing on real buildings not claims from a labs media department? Here's a link disprovi…

Your link seems to be discussing paints that reduce conductive losses (paint with insulating additives) between the paint and the ambient air, whereas I believe the person you were responding to was describing paint that optimized radiant losses between paint and the visible sky and reduce reduce gains from the sun, which are independent of ambient air temperature.

For example, there's a reason so many buildings in the Mediterranean are painted white going back to antiquity.

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