I had heard of this before, but I wasn't sure if it was even true! Now it's being developed into a new technology.
@#12, I'm sure you'll find it a very interesting article.

https://www.newscientist.com/articl...ioning-could-work-by-beaming-heat-into-space/

 

Interesting.
But achieving the large radiative area in a vacuum chamber with a large IR transparent window needed for reasonable heat radiation could be problematic to do at a practical cost.
I think the amount of heat energy radiated by this method is quite small on an area basis.

 

More typical pie-in-the-sky ivory-tower dreaming.

They go out of their way to thermally isolate the space being cooled using ten heat shields, superinsulation, and vacuum chambers pumped down to the microtorr range so that they can achieve the smallest parasitic heat load they can in an area about the size of a soup. They don't mention the cooling power they achieved, but it was probably in the sub-watt range by quite a bit. Then talk immediately starts about using this to cool large office buildings, even though the paper itself states that significant temperature reductions require ultra-low parasitic heat losses. In fact, in the presence of parasitic heat loss typical of "unsophisticated" experimental setups (which by most standards would be pretty damn good, just not ultra great), their approach achieves almost the same performance as other previously demonstrated radiative approaches (about a 10°C differential) -- and that's still for a sealed, isolated chamber. Quite a huge leap for any kind of thermal throughput like even a small air conditioner would need to handle.

 

Right. I call BS.
The "parasitic" heat in this case is millions of BTUs per hour.
There is no mention of BTUs per square foot of radiator surface.
Wouldn't it be lovely to have a magic heat window into outer space!
A square foot of magic IR radiator replaces 1000 square feet of air cooled radiator coils on top of a building...
but only into a clear sky...
We could put a dozen of these in the Sonoran desert and fix Global Warming.
ROFL!

 

Thanks all for your eye-opening opinions... boy, I'm glad I'm not the one looking for investors in this technology

 

I call BS.

but you did find it interesting... didn't ya?

 

but you did find it interesting... didn't ya?

No. Mr. Pragmatic found it a waste of time.

The mere mention of air conditioning was a red herring the size of Montana.
Nothing but click bait.

 

No. Mr. Pragmatic found it a waste of time.

The mere mention of air conditioning was a red herring the size of Montana.
Nothing but click bait.

... bummer.... perhaps I could get you interested in investing on very a very attractive piece of land on the moon instead?

 

a very attractive piece of land on the moon

Well, that would guarantee a clear sky to facilitate radiation.

 

Well, that would guarantee a clear sky to facilitate radiation.

And no need for a vacuum pump.

 

I found this interesting only because my dad used to tell me about an exam question he had in a chemical engineering class. It asked what is the highest temperature at which you can still get frost to form on a surface. I believe the answer was 40°F, after a few simplifying assumptions. Of course the only reason it is so high is because of black-body radiation to space. It's certainly a relevant phenomenon, but it's already in wide use!

 

I found this interesting only because my dad used to tell me about an exam question he had in a chemical engineering class. It asked what is the highest temperature at which you can still get frost to form on a surface. I believe the answer was 40°F, after a few simplifying assumptions. Of course the only reason it is so high is because of black-body radiation to space. It's certainly a relevant phenomenon, but it's already in wide use!

I'm guessing wind chill also plays a role?

 

This is just the opposite of the 'Sydney Tube' solar hot water collector, which is a tube in an evacuated tube, that gets VERY hot in sunlight. I saw a demo where oil in one was used to fry eggs. They are used all over the world now for solar hot water.

This cooling device is simply something that gets cold when exposed to the clear sky. It's a brilliant idea. I've no idea of what it costs to make, or it's lifetime, but the performance is interesting, from:

https://arpa-e.energy.gov/sites/default/files/Day 1 radiative cooling - Aaswath Raman.pdf


Your department of energy commissioned a study www.pnnl.gov/main/publications/external/technical_reports/PNNL-24904.pdf that suggests (in the executive summary) that for a 5000m^2 office building:

Relative to the VAV system, the proposed photonic radiative cooling system saves 103 MWh electricity in Miami, 55 MWh in Las Vegas, 50 MWh in Los Angeles, 24 MWh in San Francisco and 43 MWh in Chicago, per year. The saved electricity represents 50%, 45%, 65%, 68%, and 55% of the VAV system cooling electricity, respectively in the above five cities.

So it's not BS or junk science, the physics is sound, the economics are uncertain.

 

I'm guessing wind chill also plays a role?

No actually you need very still conditions so that convection doesn't warm your surface. And wind chill only affects a wet surface. You can protect a plant from frost by misting it with water.

 

So it's not BS or junk science, the physics is sound, the economics are uncertain.

It's a very clever way to get more value out of the evacuated tubes in a solar collector of that type. I saw a prototype installation years ago but haven't seen much since. I think the players went out of business.

 

So it's not BS or junk science, the physics is sound, the economics are uncertain.

From what I understand, it's the technology itself that would be extremely hard to implement in an economic and reliable way.

 

Well, to do what they did in the lab would be tough. But as noted, there has been a commercial product that comes very close, a black body radiator inside an evacuated clear tube.

One of the things limiting the efficiency of any air conditioner is the size of its heat exchanger. If I could run my hot freon lines somewhere over the house so that they could radiate to space at night, I would absolutely increase the efficiency of my A/C system. But piping and heat exchangers cost money.

 

Your department of energy commissioned a study www.pnnl.gov/main/publications/external/technical_reports/PNNL-24904.pdf that suggests (in the executive summary) that for a 5000m^2 office building:

Look at page 35 for a graph showing 10% effectiveness for Miami in June, July, and August.

Considering where I am, and what I'm used to calculating for, that justifies my instinctive reaction in post #7.

 

Yeah, you need dry air above you to get much radiation.

 

Yeah, you need dry air above you to get much radiation.

Dry and clear... I'm sure pollution level is a factor too.