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!)
That's why he insulates his box from the hot planet and enjoys the fact that the air is largely IR-transparent.
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!)
> as the nearest surroundings are the hot planet, which transfer heat more effectively! The box is insulated. In one case it's an unused refrigerator that opens on the top with more insulation apparently surrounding it. The planet may be hot but on a cold night the ground does nothing to warm me. Soil is not a good conductor of that heat at the surface nor is the air between it and the container. The planet stays "ho…
The ground does a lot to warm you, radiating terrestrial temperature BBR to your entire lower hemisphere, basically it's the same ~100W/sqm.
Sleeping under some tree cover on a clear night vs sleeping under the clear sky makes heaps of difference.
Why isn't this replacing aircon over the whole world? Unless that IR-transparent window is made of gold dust, it has to work out cheaper than the energy cost of running an air conditioner.
Adding to everyone else, but local climate makes a big difference. This isn't very useful unless you have dry still air, and it works best at night, but could maybe work during the day if you have a good view of the sky but have blocked the sun. Most places with dry still air don't need specific cooling at night, because "everything" already cools due to this effect, and it doesn't stay hot for long after the sun goe…
> Most places with dry still air don't need specific cooling at night, because "everything" already cools due to this effect, and it doesn't stay hot for long after the sun goes down.
Exactly this. This is reflected as well in the article, even if not promintently: they have 30C Celsius at midday (which is hot) and 4-5C at night (which is cold). 25C between day and night is close to desert behavior as far as diurnal air temperature variation [1] is concerned.
One phenomenon I've found peculiar on frosty mornings is that the grass directly under my (apple) trees doesn't freeze, leaving a noticeable silhouette on the lawn. I've assumed it was due to the cool, heavy air falling and the tree acting as a shield but this article makes me think there are more complex factors at play.
With the exception of two vacations to California, I have lived my entire life in high humidity locations. This sounds like magic, I understand the science and all, but that it can actually work is wild. It might work for me in the winter, when we regularly get drier weather and spend a most nights flirting with freezing.
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…
You might like NightHawkInLight's videos on the topic[0] and Tech Ingredients[1] - they've been working on making paint using this technology with an at-home DIY process and experimenting with it. [0] https://www.youtube.com/watch?v=KDRnEm-B3AI&t=285s [1] https://www.youtube.com/watch?v=dNs_kNilSjk
If you insulate it in vacuum with an IR transparent window (unfortunately $$$) you can get substantially cooler than ambient: https://www.nature.com/articles/ncomms13729
Could this be used for power generation at large scale, while cooling the Earth at the same time?
Here in Brazil we use a system with copper pipes in an insulated "box" to heat water during the day using this energy from the sun. A couple of years ago, in a cold winter day with a minimum of 5 degrees (celsius), just after the sunrise the water froze, broke the pipes and the glass above it. I couldn't understand what happened because the ambient temperature was above freezing point, maybe it was something like thi…
Fascinating! That does seem like the most likely explanation. This reminds me of the ancient ice ponds that made ice thousands of years ago in Persia. I read somewhere that they were able to make ice through a combination of radiative and evaporative cooling at night temperatures around the same as you experienced, about 5C.
Yes, I like this explanation, when that phenomenon happened in our house I thought one of our neighbours was dumb because he just put a blanket over the collector on the roof, as he said, "to keep it warm". But now I think he was right. Now, I don't know if this exists but it would be nice if there was a kind of glass that let radiation pass only to one side and not the other way, a kind of "valve", this could solve the problem of water frozing from radiation in our solar heating.
If you insulate it in vacuum with an IR transparent window (unfortunately $$$) you can get substantially cooler than ambient: https://www.nature.com/articles/ncomms13729
Could this be used for power generation at large scale, while cooling the Earth at the same time?
Consider this: quite powerful solar thermal generators [1] and furnaces [2] have been built, which use mirrors to concentrate sunlight. Do they create intense cold at night? No, because you can't focus coldness. The device in the article, and the one described above, depend on shielding a volume from terrestrial heat sources, and are effective only because the heat being transferred is minimized.
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…
Fascinating! That does seem like the most likely explanation. 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.