But: During the day, is the sky actually colder than ambient air? ChatGPT4 says it's not: " However, even when considering a part of the sky that is not directly exposed to sunlight, the sky temperature during the day is generally still not lower than the ambient air temperature. This is because the Earth's atmosphere absorbs and scatters solar radiation, which warms the air and contributes to a higher sky temperature even in areas far away from the sun"
Is it hallucinating and you found other data?
Also, even if it is a few degrees colder, the radiative cooling effect would be minimal, since heat transfer is proportional to DeltaT**4.
I read somewhere that it might work for other wavelengths... and indeed:
"The Earth's atmosphere consists of several gases, such as water vapor, carbon dioxide, and ozone, which absorb and emit radiation in specific wavelength bands. These absorption bands are known as "atmospheric windows," and they allow certain wavelengths of IR radiation to pass through the atmosphere with minimal absorption. For example, the 8-13 micrometer wavelength range is one of the most prominent atmospheric windows in the IR range.
If a surface can selectively emit thermal radiation in these atmospheric window regions, it can achieve radiative cooling even during the day because the emitted radiation can escape into space without being significantly absorbed by the atmosphere. In this case, the sky temperature, as seen by the surface at these specific wavelengths, can be lower than the ambient air temperature, allowing the surface to cool down.
Developing materials and coatings that have high emissivity in these specific wavelength bands and high reflectivity in the visible and near-infrared range (to avoid solar heating) is an area of active research in the field of radiative cooling. These materials can potentially enable passive cooling of surfaces during the day, even in the presence of sunlight."
GPT4 is making stuff up. Go watch the video I linked at the beginning, it explains the same technique but with using a water cooling loop instead of just connecting directly, which makes sense if you need heat during the winter but is very inefficient otherwise. There are also some paints which are specifically used for this and there are videos about those as well, which may be the materials its referencing and would be a reasonable layer to go between the thermally conductive one and the polyethylene
As a New Englander, my knee jerk reaction is "That will perform poorly with snow."
I did say specifically Los Angeles. In New England cooling is rarely the issue.
Great idea!! Simple and beautiful.
But: During the day, is the sky actually colder than ambient air? ChatGPT4 says it's not: " However, even when considering a part of the sky that is not directly exposed to sunlight, the sky temperature during the day is generally still not lower than the ambient air temperature. This is because the Earth's atmosphere absorbs and scatters solar radiation, which warms the air and contributes to a higher sky temperature even in areas far away from the sun"
Is it hallucinating and you found other data?
Also, even if it is a few degrees colder, the radiative cooling effect would be minimal, since heat transfer is proportional to DeltaT**4.
I read somewhere that it might work for other wavelengths... and indeed:
"The Earth's atmosphere consists of several gases, such as water vapor, carbon dioxide, and ozone, which absorb and emit radiation in specific wavelength bands. These absorption bands are known as "atmospheric windows," and they allow certain wavelengths of IR radiation to pass through the atmosphere with minimal absorption. For example, the 8-13 micrometer wavelength range is one of the most prominent atmospheric windows in the IR range.
If a surface can selectively emit thermal radiation in these atmospheric window regions, it can achieve radiative cooling even during the day because the emitted radiation can escape into space without being significantly absorbed by the atmosphere. In this case, the sky temperature, as seen by the surface at these specific wavelengths, can be lower than the ambient air temperature, allowing the surface to cool down.
Developing materials and coatings that have high emissivity in these specific wavelength bands and high reflectivity in the visible and near-infrared range (to avoid solar heating) is an area of active research in the field of radiative cooling. These materials can potentially enable passive cooling of surfaces during the day, even in the presence of sunlight."
(ChatGPT4)
GPT4 is making stuff up. Go watch the video I linked at the beginning, it explains the same technique but with using a water cooling loop instead of just connecting directly, which makes sense if you need heat during the winter but is very inefficient otherwise. There are also some paints which are specifically used for this and there are videos about those as well, which may be the materials its referencing and would be a reasonable layer to go between the thermally conductive one and the polyethylene
Yeah, as usual it's a bit more complicated, haha. Here is a paper that I sadly don't have time to read right now: https://www.researchgate.net/publication/332459395_Radiative_sky_cooling_Fundamental_principles_materials_and_applications
Curious where this thread goes... :-) Thanks for posting.