New Metamaterial Enhances Natural Cooling Without Power Input

I don't see that this deals with ambient air temperatures and relative humidity, a must for building environmental control...We have reflective coatings, that merely lower the heat load a bit, but frankly a well insulated attic space and ventilation below the roof are much more effective....The roof must be able to withstand all the weathering elements and dust and dirt that precipitate from the sky and reflective surfaces require a clean environment, or constant maintenance....much better to use the roof space for some solar panels imo....

"...much better to use the roof space for some solar panels imo...."

Which also require a clean environment.

So, will it make my house colder in the winter?

It would cool your house in the winter if you just coated the roof with it. It would be only used in the summertime using circulating water.

I thought this was interesting, but I'm not sure it's practical. You can only move so much heat via radiation.

I agree with all but your last statement. Nearly all of the heat (energy) on this planet came via radiation at one time. I'll grant you that very few things on this planet have similar black body radiation spectra as the source shining on my desk through frosted glass nonetheless all of that transferred through the vacuum of space using only radiation, the least effective method of heat transfer.

Yeah, I was thinking of the application of cooling a building. As you say, radiation is the least effective method of heat transfer. Forced convection (fans) are more effective in the atmosphere.

We just had our (previously grey) roof replaced with a very white vinyl one. We also have a thermostatically controlled fan in the attic. During the installation and even more after the roof was replaced, we had (hopefully) the last major heat wave of the year. I can definitely say that the fan came on less frequently (as did the A/C) after the new roof was put on.

This is effectively saying that it may be better to prevent the heat from coming in to start with, than to try to get rid of it later, using whatever means.

It may be hard to determine whether we will need additional heating come winter...

If there is an obvious difference, I'll post it here.

White roof will not cause the house to lose heat in the winter more rapidly. That takes place primarily through doors and windows. Infrared thermography has proved this over and over.

Local albedo (white roof) can and should make a difference in the summer. Have you ever tried reading solar reflectivity of an asphalt composite shingle? I would be shocked if the reflected energy is more than about 20%.

That's what I'm expecting. This winter, I'll check it out. I do have an IR camera (FLIR One for IOS). Unfortunately, I didn't think to take pictures last winter with the old (tar and grey gravel) roof. I do have a couple of images of the house, but didn't include the roof.

I didn't think to try to set up an experiment to measure the albedo at IR wavelengths. I do still have some of the gravel, and a sample of the new roofing material, so I could do that this winter. I'll set aside some of the gravel so it does not get contaminated.

Use your snow gauge..., i.e., the rate at which snow disappears off the roof, which could be an additional factor in not selecting a white roof, especially if large frequent snow events take place. If no snow, then you are good to go.

I like you experimental design ideas. They sound reasonably sound for a quick and not so dirty answer.

We do occasionally get snow. The greatest depth was 15 inches in 2008. The previous greatest depth was 7.5" in the mid-70's. Yes, we've lived in the same house since 1970.

I understand (a neighbor told me) that the Farmer's Almanac is predicting a colder and wetter winter than last year. That's significant, since we had over 200% of normal last year! If so, I should be able to test the theory. The NWS has predicted snow for next week in the Sierra just east of here, which could be a start...

Just yesterday I picked and crushed grapes for this year's wine. I should have done it a week ago; the birds really took their toll. So the grapes are early, and a lot of leaves are falling already. Time will tell whether those are significant factors!

Presumably Lake Tahoe. It is by far the largest, and it is surrounded by many high peaks, ski resorts, and (on the Nevada side) casinos, but there are many other smaller ones, like Fallen Leaf, Union Valley, Ice House, Loon, Caples, and Silver. I've been to all of them except possibly Loon.

These are all high altitude lakes (by most people's standards), and I love high altitude. Unfortunately, my wife gets nosebleeds above 6k feet, so I don't go there nearly as much as I'd like!

The one we were on had houseboats primarily, was not a small lake (by my standards), although I recall being able to see the opposite shore from either side. Clearest water in a deep lake I have ever seen, with beautiful, large trout swimming in plain sight. There really is some good eating in there!

There were lots of hydraulic mining that had been done on the west slope coming away from the lake toward the valley. I think we were north of Fresno, and now I cannot really identify the lake. It seemed to be fairly well up in the hills, not quite to the Sierras. Chowchilla was the town where her relatives were living.

We have hydraulic mining scars right here in Placerville, but not at any of the lakes I mentioned.

Millerton Lake is north of Fresno and roughly east of Chowchilla, but I don't remember any hydraulic mining that far south.

Farther north are Lake McClure, Don Pedro Reservoir, and New Melones Reservoir. That last one is just off Hwy 49 south of Angel's Camp. There is definitely mining in that vicinity.

It almost has to be Lake McClure area. I must have been smoking something really good like banana skins when I drove up there. LOL

"...Farmer's Almanac is predicting a colder and wetter winter than last year."

I noticed that my cat already has a nice thick coat, and it's only mid-September.

Since a neighbor told me, it's already third-hand news. I assume that she was reading about predictions for our region (Western US, CA, or even Northern CA), but you probably know how dangerous it is to assume.

We either have a very small acorn crop, or they haven't started falling significantly yet. I think I remember that the acorn crop was supposed to signify something about the coming winter, but I don't remember which way the prediction was supposed to go...

Sounds like you have a healthy cat!

Generally lighter colors tend not to radiate heat, and your fan should not come on during the winter months, so I doubt that there will be any significant increase in need for heat.

Yes. Also will make it colder in the summer if that is what you want.

Radiation of infrared is not the same as conduction of heat, or convection. This thing is not transferring energy to the air mass (as such), but is radiating to the "black body" of the upper atmosphere and/or outside our atmosphere. According to Planck's laws of radiation, net energy flow is always in favor of radiation from the hotter source to the cooler. Since the material also reflected incident light, it lowers the thermal gain of the structure.

I thought this was an interesting topic, so I decided to look into it. Some things I did and did not find.

Cost is approximately 0.50 per meter/2.

Dr. Yin has a published white paper that can be downloaded describing how this works.

Dr. Yang says that a building can be wrapped with this film, but the building would also need to be wrapped with cooling/heating pipes ( water circulation) so the efficiency of the film doesn't cool the building in the winter.

I couldn't find information on how the material would be attached to a building or information on how or if the material can be recycled.

I went to Google.

1. Colorado.edu

2. Physics world

3. Science magazine

4. Construction dive

5. Chemistry world

6. LinkedIn > pulse > new > metamaterial > en...

Why not make this stuff more like venetian blinds, only make it so it can cover over 90% of the building (film in frames for slats).

Where can I find Yin's white paper?

Couldn't find a link to original paper but found a good article on

Green Building Advisor.com

Here's another team working on this: http://news.stanford.edu/2017/09/04/sending-excess-heat-sky/

And they've already put it on the market! http://skycoolsystems.com/

Interesting with two such similar projects funded by the same agency.

Here are those URLs converted to links:

http://news.stanford.edu/2017/09/04/sending-excess-heat-sky/

http://skycoolsystems.com/

It's a pretty big stretch to say they've "put it on the market.". It looks more like they are trying to find one. I didn't "sign up", but I don't get the impression that anyone can go somewhere and buy a system yet.

These panels would work best when placed in a horizontal position, as on a flat roof, but that is also the position that will collect the most dust, leaves, etc. Dust and leaves would reduce both the reflectivity of sunlight and the emissivity of IR, so they will need regular cleaning. There went that zero water claim!

The immediate take-away I got from the first link is: These panels can cool circulating water to below ambient air temperature. Does anyone else here see what that means?

It means there is a viable replacement for evaporative cooling systems in processing plants and power generation plants all over the world is what it means.

This is a gigantic water-resource saving technology. Ok, so it might take up considerable land to get the final temperature below ambient, but most of the cooling could take place by simple air exchange to within δt of ambient, then the radiative cooling could finish cooling all or part of the water further down, to improve cycle cooling efficiency.

True, within limits, and using water-free or very-low-water methods of keeping the panels clean. On the other hand I don't believe my brother ever cleaned the PV panels he put on his garage about 20 years ago, and they are still working, as far as I know. They are tilted at ≈20°, which may be enough for the rain to do the cleaning in his area east of Fresno..

Since these panels reflect virtually all of the sunlight, perhaps it would be effective to put vertically oriented strips of small PV cells crossing the cooling surfaces, and thereby generate both cooling and electricity from the same area...

I didn't see any numbers for the volume of water cooled per unit area per time.

when you consider the temperature gradient this operates over, the cooling rate (power) per unit area cannot be that large. Just large enough to be important.

Could this material be used in the manufacture/fabrication of plate type heat exchangers which would circulate cooling water?

That's precisely what they are doing right now.

I see no reason why it could not, hence it fits well into the idea of process cooling without using evaporation of the water.