back
206 comments
In Japan they have these portable AC jackets. I believe they are mainly used by people working on building sites where it gets very hot in summer. While these are actively cooled rather than passively (as in the article), they seem like a better idea than air conditioning whole rooms.

https://wonderfulengineering.com/japanese-invent-a-jacket-wi... https://www.dailymail.co.uk/sciencetech/article-2016513/Japa...

(Sorry can't find any good links - the jackets aren't a fad and seem to be popular with builders)

Edit: The company website (Japanese) https://kuchoufuku.com

> "...they seem like a better idea than air conditioning whole rooms."

in the same vein, most people's behavior around heating/cooling is comically misguided and inefficient. most people believe temperature is what we're trying to control, and that's driven by how weather reports, climate controls, and even our language ("it's hot!") emphasize temperature (which isn't nefarious, and makes sense in their separate, respective domains) rather than heat transfer, which is what we're really after.

this is most evident in cars, where folks point air vents away from themselves while running the a/c (or heat) full blast, rather than pointing the vents at themselves and running at a lower speed. the former is based on the idea that the whole car's interior temperature needs to be lowered (or raised) for effective heat transfer away from (or to) the body, which is incorrect and inefficient. pointing the vents at you (on bare skin ideally) promotes heat transfer immediately instead of waiting to create a big enough temperature differential to do the same work.

I have seen these and pondered if it is rude to wear them. While it is actively cooling your body, you are aggressively blowing your heat to those around you. In a crowded subway train I would not want to be next to someone wearing this. However, perhaps I overestimate their effects.
It looks like it's more of an air "cooler" than an air conditioner. It probably works somewhat depending on the climate, but air conditioning actively cools the air (it produces colder air than the exterior air temperature) and reduces humidity.
> they seem like a better idea than air conditioning whole rooms

Is that really true? It's more efficient to cool larger rooms, because their surface area to the outside world is lower relative to the volume of the room.

Keeping entire factories or warehouses cool uses surprisingly little energy. Once they reach the desired temperature they stay there with only minor additional cooling.

Also, a ridiculous review of these by AvE (a channel I recommend to anyone who’s mechanically inclined): https://youtu.be/ySw0IHIwQ3s
The only device that gets that small is a Peltier cooler, and those have far less efficiency than a proper Air Conditioner / Refrigerant based pump.

You can experiment with Peltiers yourself: they're widely available on Digikey and are extremely small and effective at "air conditioning" like tasks (moving heat to the hot side, while cooling the cold side).

But due to their lack of efficiency, they can never properly compete against a large scale central air conditioner: be it a proper dehumidifier, refrigerator, or actual AC / HVAC unit.

-------

A 100W Peltier might be able to move 50W (meaning the hot-side is 150W of heat, while the cold side is -50W of cooling). Perfect efficiency (50W heat hot side / -50W of cooling cold side) is impossible, much like perpetual motion machines.

In contrast, a proper air conditioner might be closer to 100W of power delivering 300W of cooling (Emit 400W of heat on the hot side, and provide -300W cooling on the cold side).

Furthermore, the temperature difference from a Peltier is small, maybe 10C or 20C (and the bigger the delta, the less efficient a Peltier gets). A proper compressor / refrigerator can handle much larger temperature differences at much higher efficiency.

-------

So the key for Peltier is to find low temperature differences (maybe keep it to 10C to minimize the efficiency loss), at low-wattages (so that the inefficiency won't generate too much heat). Maybe 10W to provide -5W of cooling (cold side) and 15W of heating (hot side) which won't raise the temperature of the room too much, and still provide some degree of comfort to the people wearing the jacket.

But its clear to me that "air conditioning" is one of those "bigger is better" deals. You'd rather more centralize the hot-side vs cold-side (ex: make sure the hot side is outside, rather than having many hot-sides inside fighting each other, raising the temperature of the room you're working in)

There are also cooling vests packed with ice or other substances e.g. PureTemp from Glacier Tek [1], although I wonder how good are these compared to the traditional ice.

[1]: https://glaciertek.com/

Funny seeing all of the comments span multiple years asking to buy or distribute this product.
Is that shirt effective when it’s 40 degrees outside? I have noticed that the fan stops working for me after certain temperature.
I can't remember the exact situation, but it's better to keep a gigantic house at temperature than to let it get far out of temperature only to be recooled.

With something like this you'd need near constant cooling. Although still you are only cooling a small volume, so it could be better.

they have something like this but full body - for those people who wear the full body mascot outfits eg games/ Disney etc..
Okay heat map is cool, but what does it look like? any different?

Also how does it breath? Natural cotton shirts still feel the best to me. I hate Rayon.

I'm interested in this because I currently live in Singapore where it's sunny, annoyingly hot and humid all year round. I'd welcome something like this when I'm outdoors.

Just too light on the details.

One thing I noticed is that their control was a cotton shirt "about the same thickness" as the new one. But the new shirt is "550 micrometers" thick, which is about twice as thick as a regular T-shirt. So maybe they're tilting the scales a bit to make the cooling effect seem a little better?
Looking at the pictures in the scientific article it doesn't look particularly weird, just a white cloth: https://science.sciencemag.org/content/early/2021/07/07/scie...
Unfortunately this new fabric only helps with the "sunny" part (it keeps you cooler when you are exposed to direct sunlight), but not with the "hot" and "humid" part...
Yeah the lack of even a regular color photo is weird.
PSA: Patagonia makes these fantastic lightweight "Capilene cool daily" short- and long-sleeved t-shirts that feel like they must have some magical active cooling built in along with their SPF 50 protection. I don't know how they did it, but I own half a dozen and will continue to gift and recommend them as the greatest t-shirts ever made.
They are UPF not SPF and recently they announced a voluntary recall because they weren't actually UPF 50.
Older Patagonia "Capilene" material have undesirable "odor retention" feature. Patagonia claim the updated version does much better. Do you have any experience between the new vs old (circa ~2000-2005 version)?
Thanks for the suggestion, I’ve been looking for a shirt that keeps me cool for a while, I just ordered one!
The Uniqlo Airism line has some extremely light and breathable shirts. The "micro mesh" ones are insane. But the style is not going to be everybody's taste, unlike the Capilene shirts which pretty much just look like a normal t-shirt.
Various manufacturers make UPF clothing, Outdoor Research, Kuhl, and Black Diamond are some. REI's house brand has worked well for me, though the fit is baggy.

A white cotton t-shirt is said to be SPF 15.

Never thought I'd read about Patagonia clothing on HN of all places. /s
The headline is somewhat inaccurate, the fabric reduces the heating by the sun by 5°C, which is still useful of course.
Wonder how it holds up to laundering/drying.

Remember those shirts that changed color based on temperature but couldn’t be put in the dryer?

I wonder if it would be useful for things like curtains or overhead canopies, adding some passive cooling to spaces to reduce the need for mechanical cooling
I wonder why they haven’t tested a full model? They say the cost is low and production is easy, so why not do that to prove it works before going to manufacturers?
Just to point out the obvious: this ain’t gonna make a blind bit of difference if wet bulb temperatures enter the kill zone, so do not rely on this to protect you from the effects of climate change.
Great to see the academic tradition of roasting graduate students as an experiment is being carried on. :)

Seriously now, as someone who occasionally spends a good while walking about in direct sunlight, I'm really interested in this, especially since I have noticed a marked increase in temperatures over the last few years and my Summer walks have become quite arduous...

I've been waiting for something like this my entire life. I hope that fabric is good enough for producing underwear.

Not even remotely overweight but I produce a considerable amount of extra heat. Seriously, whoever starts selling panties that cool my junk is going to be rewarded handsomely

The need for the material to be tight fitting isn’t actually a problem for athletic wear. If you’re wearing a wicking shirt you would also want it to be tight fitting. And a lot of rash guards will be tight because they wick in addition to providing uv protection. So I’m skeptical that the researchers really understand the applications for their material. There’s also no discussion of how it performs when it gets wet.
If it is like a mirror then what about people around you getting all that light reflected back into their eye - light which they can't really "see"? Seems like if you are around something like that all day where multiple people are wearing such clothes that it could possibly be damaging?
If this sends the heat into space, what happens if you’re indoors? Would it still cool you?
I can honestly say this is the most exciting article I've read in a long time. Can't wait for this to be commercially available.
Can it be used in reverse to keep the body heat in instead? If the body is producing the radiation, it should be usable in reverse.
I need a pair of boxers made from this stuff.
I wonder how they do against UVA and UVB.
The military will love that stuff. Could you drape it over vehicles as well to hide from infrared optics?
The paper: https://advances.sciencemag.org/content/3/11/e1700895

And the paper for nanoPE: https://science.sciencemag.org/content/353/6303/1019

... TLDR, they sandwiched a reflective and emissive surface inside of a thermally transparent material. Body heat convects to the surface (so it needs to be tight fitting), and the surface is radiatively coupled to the environment (emissive surface), but not to the body (reflective surface). You lose out on directly radiating body heat through the nanoPE, but that doesn't work well anyway.

Anyway... it probably wouldn't work very well if the ambient temperature was high since it is absorbing LWIR from the environment. The article does mention MIR (MWIR) a few times, though. There isn't anything MWIR specific with this fabric, but the atmosphere is generally very cold in that band, so maybe LWIR can be reradiated in the MWIR by the fabric even when the ground temperature is at/above body temperature. The blackbody power in the MWIR at 98.6F is pretty poor, so it can't be much.

They used an ambient temperature of 22.0C in the paper, which is kind of cheating (why bother with a cooling shirt at that temperature?). The LWIR coupling will help a lot at that temperature. Once the ambient gets close to human body temp, though, it'll not work nearly as well. One could run the numbers to see, the thermal model is pretty simple.

All that's needed now is to produce enough of it wrap it around the earth.
The interesting part is how big are the environmental costs of the production?
IANAS, but I'm puzzled by the use of the word "cooling". This fabric doesn't actively cool the wearer, or reduce the temperature, it simply prevents temperature from rising, keeping things up to 5 degrees cooler, if they were already cool to begin with.
Or just use linnen...
Can I put this around my CPU?
BootStrap website really needs this in the documentation for its components
They are talking about the atmospheric window - the band of EM/heat that can be freely radiated out to space unblocked by our atmosphere.

This is an important concept in global warming/ghg that you almost never see discussed. The band that CO2 absorbs (15 microns mainly) is not in the atmospheric window. The 15 microns band is already absorbed by water vapor, and is almost 99% saturated as is.

(This is where some particle physics students stop talking so they don't upset people)