61–70 of 94 posts
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If it's either 36C or 36K at night, you've made a bad decision on where to live.
Don't forget Rankine, although you are making equally bad decisions as Kelvin there
Earlier quoted context omitted.
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 int…
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)?
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.
Earlier quoted context omitted.
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 int…
> 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?
Many years ago, I had an indoor swimming pool with solar heating. Some days in the middle of summer that water got too warm. So I'd run the water through the black plastic solar collectors at night-time to throw away that excess heat.
We also thought it was too cold to swim if the air temp was below 35C (95F).
Australia.
Many years ago, I had an indoor swimming pool with solar heating. Some days in the middle of summer that water got too warm. So I'd run the water through the black plastic solar collectors at night-time to throw away that excess heat.
I’m missing the basic premise here, how does pointing an insulated box at the sky at night cool whatever’s in the box?
A black body will emit radiation (and receive radiation) until it's in equilibrium with its surroundings. In theory, the black bit of box radiates heat into space, and receives some of the CMB until both are at ~3K. It's how we cool satellites and spacecraft. But the effect is quite small, and I'm suspicious of it (as the nearest surroundings are the hot planet, which transfer heat more effectively!)
If you insulate it in vacuum with an IR transparent window (unfortunately $$$) you can get substantially cooler than ambient: https://www.nature.com/articles/ncomms13729
Checking my understanding here: in a very simplified sense, is this saying that we’re taking energy, be it from ambient temperature during the evening or that plus solar radiation during the day, and essentially bottlenecking/‘forcing’ it to radiate in the spectrum that’s atmospherically transparent and can thus escape to space? Seems the use of insulating it in a vacuum would be to minimise heat loss until it’s cool…
If you insulate it in vacuum with an IR transparent window (unfortunately $$$) you can get substantially cooler than ambient: https://www.nature.com/articles/ncomms13729
Here in Brazil we use a system with copper pipes in an insulated "box" to heat water during the day using this energy from the sun. A couple of years ago, in a cold winter day with a minimum of 5 degrees (celsius), just after the sunrise the water froze, broke the pipes and the glass above it. I couldn't understand what happened because the ambient temperature was above freezing point, maybe it was something like thi…
This reminds me of the ancient ice ponds that made ice thousands of years ago in Persia. I read somewhere that they were able to make ice through a combination of radiative and evaporative cooling at night temperatures around the same as you experienced, about 5C.
If you insulate it in vacuum with an IR transparent window (unfortunately $$$) you can get substantially cooler than ambient: https://www.nature.com/articles/ncomms13729