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Comment by DayDollar | Hacker News Reader

So what can create dry air? Circulation chimneys and cool caverns were the moisture runs down the wall? I wouldnt want to rely on electricity in a wet-bulb.

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Finding ways to cool the air down without electricity might be easier. If nights are still cold you can use thermal mass to get a long-term temperature average (kind of like your caverns). The ancient Persians combined that with evaporation cooling to create fridges. There are also specially engineered paints that radiate heat energy in very specific wavelengths that aren't absorbed by the atmosphere, breaking the equilibrium between absorption and emission of IR and cooling the material by a couple degrees.

I think there are two ways to deal with getting moisture out of the air: 1. desiccants 2. cooling it down past saturation

Desiccants aren't nearly effective enough to dehumidify something like a room. [EDIT: apparently desiccant dehumidifiers are a thing too, although much less common in the home consumer world, so never mind -- disregard this whole comment!]

The answer is #2. Air conditioning units and dehumidifier units, which are essentially the exact same thing except for where the hot air output goes. (AC's send the hot air outdoors; dehumidifiers mix it back with the now-dehumidified cold air.)

> Desiccants aren't nearly effective enough to dehumidify something like a room.

I'm not sure this is true. There's some nasty desiccants that can work effectively, but the trouble is usually in regeneration.

ACs don't send the hot air outside. They transfer the heat outside. They usually recirculate the inside air. But the act of running the inside air across the cooling coils causes water to condenser on the coils and thus dehumidifies the air as well.

If portable A/C units aren't sending the internal air outside, does that mean they're also just circulating outside air as a way to disperse the heat, rather than actually blowing air outside?

Some portable A/C units do send hot air outside, and some don't. The two-hose models AFAIK are the latter type (although the un-insulated hoses are wildly inefficient)

https://youtu.be/_-mBeYC2KGc

And compression

I think electric dehumidifiers are way underused. In a cool wet climate, they're really all you need to stay comfortable down to the 50s. Anywhere you have cold wet air, it can be converted to dry warm air much more efficiently than resistive heating with those things.

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