5 ms·

This can also be used to heat and cool a building. Harold Hay experimented with a "Skytherm roof" back in the 1970s and built a house at Atascadero, CA. https:

This can also be used to heat and cool a building. Harold Hay experimented with a "Skytherm roof" back in the 1970s and built a house at Atascadero, CA. https://www.sciencedirect.com/science/article/abs/pii/S0960148199000798 https://www.sciencedirect.com/science/article/abs/pii/S09601... Harold Hay LA Times article: https://www.latimes.com/archives/la-xpm-2007-nov-10-fi-haroldhay10-story.html https://www.latimes.com/archives/la-xpm-2007-nov-10-fi-harol...

madaxe_again 3y ago
This is how buildings heat and cool, mostly - every part of a structure that can see the sky allows radiative heating AND cooling. People forget about the second part. And this is why we built our current house on a north facing slope, in a forest - against all common wisdom about siting. Place stays cool in the summer, warm in the winter - the other side of the valley literally caught fire this summer, and gets intense cycles of cooling in the winter, as it gets only ~4h of sunlight and 20h of radiation - our more sheltered side gets 0h of sunlight, but the slope and tree cover drastically reduce radiative cooling at night - it’s insane how much the temperature varies as you walk around at night, and you can feel the katabatic winds flowing down the valley and side valleys.
- coffeebeqn 3y ago
  > katabatic winds New word! So that’s what I experienced on a mountain side in Wyoming
- voisin 3y ago
  > And this is why we built our current house on a north facing slope, in a forest - against all common wisdom about siting. Can you comment or give more detail about the level of tree coverage required to have a noticeable effect of radiative cooling?
  - madaxe_again 3y ago
    Enough that the ground is mostly shaded on a summer’s day. Dappled shade, I suppose. You’re basically thinking about what percentage of the sky a given point on the ground can see, and a surprisingly small amount of cover goes a long way.
- stewpy 3y ago
  Which hemisphere are you on? If you're in the southern hemisphere do you want to have a south-facing slope(aka away from the sun)?
  - madaxe_again 3y ago
    Northern, in southern Europe. It really depends - typically a slope facing away from the sun in the temperate zone will be more heavily forested - the sunward side can be too extreme in its variation for much beyond scrub to take hold. We chose our siting based on what was best for our environment, and on noticing how the forest didn’t frost in the winter, and kept green and lush on the floor in the summer, when all else was parched. Considerations around daylight etc., followed after choosing a site. The walls facing downhill and up/down the valley are practically all window - the bedrooms, which face the uphill slope, have small windows, which are still large by the standard for housing around us.
- lukan 3y ago
  "~4h of sunlight and 20h of radiation - our more sheltered side gets 0h of sunlight, but the slope and tree cover drastically reduce radiative cooling at night" I still would always take that 4h of sunlight over 0h and just invest in better insulation. Don't you miss the sun in winter? But if you don't, well, then it makes sense. North facing sites are usually quite cheaper as well.
  - madaxe_again 3y ago
    We own both sides so the siting was by choice - the place is well insulated but having a more moderate ambient temperature outside, and having the windows shaded from the cold of space make a big difference. As to the sunlight - while we don’t get any directly into the house for 2.5 months in the winter, the far side of the valley, which is practically barren, ends up brightly lit, bringing a lot of indirect light in. Finally, for us, the summer is a killer - it can be over 40 for weeks on end, and the nights on the shadier side are much cooler, as we don’t have superheated rocks re-emitting IR, instead the canopy reflects and absorbs most of the solar irradiance. The daytime air will still be sweltering, but it doesn’t transfer heat anything like direct insolation. So the effect is more about the environment around the structure than the structure itself - although regarding the house the roof is exposed to the sky, as it’s heavily insulated and doesn’t matter, but the walls, which have a decent thermal mass being solid lumber, are always shaded, as are the windows, mostly through self-shading due to the orientation. Again, punishingly bright in there in the summer even without direct sunlight - most folks near us just eschew windows, or cover them with heavy shutters and so have no light and no view in the summer.

madaxe_again 3y ago

This is how buildings heat and cool, mostly - every part of a structure that can see the sky allows radiative heating AND cooling. People forget about the second part. And this is why we built our current house on a north facing slope, in a forest - against all common wisdom about siting. Place stays cool in the summer, warm in the winter - the other side of the valley literally caught fire this summer, and gets intense cycles of cooling in the winter, as it gets only ~4h of sunlight and 20h of radiation - our more sheltered side gets 0h of sunlight, but the slope and tree cover drastically reduce radiative cooling at night - it’s insane how much the temperature varies as you walk around at night, and you can feel the katabatic winds flowing down the valley and side valleys.

coffeebeqn 3y ago
> katabatic winds New word! So that’s what I experienced on a mountain side in Wyoming
voisin 3y ago
> And this is why we built our current house on a north facing slope, in a forest - against all common wisdom about siting. Can you comment or give more detail about the level of tree coverage required to have a noticeable effect of radiative cooling?
- madaxe_again 3y ago
  Enough that the ground is mostly shaded on a summer’s day. Dappled shade, I suppose. You’re basically thinking about what percentage of the sky a given point on the ground can see, and a surprisingly small amount of cover goes a long way.
stewpy 3y ago
Which hemisphere are you on? If you're in the southern hemisphere do you want to have a south-facing slope(aka away from the sun)?
- madaxe_again 3y ago
  Northern, in southern Europe. It really depends - typically a slope facing away from the sun in the temperate zone will be more heavily forested - the sunward side can be too extreme in its variation for much beyond scrub to take hold. We chose our siting based on what was best for our environment, and on noticing how the forest didn’t frost in the winter, and kept green and lush on the floor in the summer, when all else was parched. Considerations around daylight etc., followed after choosing a site. The walls facing downhill and up/down the valley are practically all window - the bedrooms, which face the uphill slope, have small windows, which are still large by the standard for housing around us.
lukan 3y ago
"~4h of sunlight and 20h of radiation - our more sheltered side gets 0h of sunlight, but the slope and tree cover drastically reduce radiative cooling at night" I still would always take that 4h of sunlight over 0h and just invest in better insulation. Don't you miss the sun in winter? But if you don't, well, then it makes sense. North facing sites are usually quite cheaper as well.
- madaxe_again 3y ago
  We own both sides so the siting was by choice - the place is well insulated but having a more moderate ambient temperature outside, and having the windows shaded from the cold of space make a big difference. As to the sunlight - while we don’t get any directly into the house for 2.5 months in the winter, the far side of the valley, which is practically barren, ends up brightly lit, bringing a lot of indirect light in. Finally, for us, the summer is a killer - it can be over 40 for weeks on end, and the nights on the shadier side are much cooler, as we don’t have superheated rocks re-emitting IR, instead the canopy reflects and absorbs most of the solar irradiance. The daytime air will still be sweltering, but it doesn’t transfer heat anything like direct insolation. So the effect is more about the environment around the structure than the structure itself - although regarding the house the roof is exposed to the sky, as it’s heavily insulated and doesn’t matter, but the walls, which have a decent thermal mass being solid lumber, are always shaded, as are the windows, mostly through self-shading due to the orientation. Again, punishingly bright in there in the summer even without direct sunlight - most folks near us just eschew windows, or cover them with heavy shutters and so have no light and no view in the summer.