In the other thread on cooling planters, one thing led to another and @jtd suggested using foggers to create a fine mist. I have used foggers before, and the problem with them is that the mist barely moves, so there is hardly any cooling.
But that gave me the idea of using gravity to move the mist. Also one fogger won’t be enough for a balcony. And the water can’t be too high over the fogger, or it doesn’t work, so the water capacity of the fogger is very little and it keeps running out, which can’t do in a production system. There is also the additional issue of splattering of the water.
Finding solutions for all this, my idea is to create a fogging system at a height. About a foot or so below the ceiling. The overflowing mist will be pulled down by gravity and spread around a bit by ambient breeze. For my purposes, the breeze moving the mist is not a problem. The water will evaporate faster and provide better humidity and cooling, or condense on the plants, which don’t mind. A little may be wasted from being blown out of the balcony, but short of strong windy days, I don’t anticipate this being a big problem, since the mist will be sheltered from the outside by the plants themselves.
The design of the fogger will resemble a pipe based hydroponics setup, except instead of the pots, we have misters, and the water doesn’t drain out, it is evaporated out. The circular openings will reduce the splatter, while the expansion of water into vapour will increase air pressure forcing the mist out.
The problem of low water storage is solved in two ways. One, the long pipe will contain more water in the “allowed” height. This isn’t much, because there will also be many foggers there. Two, the end of the pipe will use a right angle turn up and a bottle with a diameter so that it fits upside down can fit into it with the mouth at the appropriate water level for our use. Material of the bottle should ideally be glass or something that is sturdy. A regular mineral water bottle will crush under air pressure and release the water.
Think of upending a 20 liter RO water can into the dispenser. Like that, but bottle upturned into the water intake. This is not automatic, but it will have to be refilled less often.
Alternatively, some clever electronics, a water level sensor operating a valve or pump can refill the system when the water level goes down.
If this works well, it has the potential to replace the misting sytem for over half the year and will consume a fraction of the electricity. Unless it cools extremely well, the misting system is likely to be necessary still in high temperature/humidity conditions (it loses effectiveness too, but has to work at least minimally due to the sheer mechanics of the method).