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Comment by teruakohatu | Hacker News Reader

They appear to just circulate air around the body, which makes sweat evaporate cooling the body. If they were actual air conditioners they would be indeed moving heat from the body into the surrounding air.

Edit: to be clear I am not suggesting heat/energy disappears. In this case they are cooling the air and the body using evaporation. The system appears to suck in hot air on one side and ejects cooler humid air on the other. More or less human swamp coolers.

https://en.m.wikipedia.org/wiki/Evaporative_cooler#Physical_...

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It's the same dilemma though. Now you are raising the humidity around you, making other peoples' sweat less effective at cooling them.

Although lowering humidity can be more easily done with just ventilation.

Not really, because the body self-regulates temperature by pushing out as much sweat as it needs to reach target temperature. A tool that facilitates evaporation allows the body to get by with less sweating. The amount evaporated will be the same, but the carrier won't be drenched. (PS: roughly the same, additional heat transfered from air to dry skin will need to be shed by sweating, but I doubt that this would make much difference compared to all the watts resulting from metabolistic base load, even in absence of physical activity)

Mandatory slightly related anecdote: on a summer drive through Morocco back when car air conditioners where a thing exclusive to America and the one percent I never felt sweaty as long as the car was moving.

Yeah I rarely ever feel sweat on my body when I run. It’s when I stop running that I get drenched and need to put a headband on.

(I live in a dry climate and generally don’t sweat much anyways, YMMV)

A few years ago I stopped sweating, almost completely. Trying to cool off is nearly impossible now.

I have an ice vest if I really want to go outside for then a few minutes.

Mirror clothing sounds like a dream.

Only in poorly ventilated enclosed spaces. But the sweat usually gets evaporated anyway only slower.

And when they are used outside, the added humidity is negligible compared to volume of surrounding air.

Evaporated sweat only cools the body if it leaves the area where the body is. So presumably they would be radiating warm air away from them.

Not necessarily, they might just be radiating humid air. It's the evaporation itself that leads to the cooling.

Hey as long as I feel cool and look cool I don’t care what it does.

But the humid air makes it harder for people around you to cool evaporatively (eg. sweating)

Well yes, you must (irreversibly) increase entropy somehow. The air itself won't be warmer though.

This is why we have wet and dry bulb temperatures.

Your intuition about temperature is focused on the dry-bulb temperature that a simple probe gives you.

A wet-bulb is literally a probe with a wet cloth or tissue around it.

As the humidity in the air increases the wet-bulb temperature approaches the dry bulb temperature.

This is absolutely “warming”. The latent heat of the air increases. The sensible heat remains the same.

Without the jacket the person will emit the same heat. The jacket fans do generate a trivial amount of heat, but it’s likely less than a desktop fan.

ventilation is a lot cheaper than AC though

Isn't that just the same thing, but using a natural process (sweating) rather than phase change in a refrigerant?

Evaporative cooling also moves heat from the body into the surrounding air, just encapsulated in water droplets.

So heat goes poof?

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