TIL Ancient Persians built Yakhchāls, innovative ice storage structures dating back to 400 BC. These dome-shaped coolers used evaporative cooling to keep ice frozen even during hot summers.

You can. You can get evaporative coolers (in the US, sometimes called swamp coolers). I have one. They use much less power per unit of cooling than air conditioners, but come with some drawbacks:

You can only cool so far (well, you can build multi-stage systems to cool further, but then power efficiency drops off). Air conditioners don't have such a limitation --- throw more power at them, and they'll make air colder.
You must have low humidity, so that the water can evaporate. At 100% relative humidity, they're totally inoperative. Air conditioners don't have this requirement.
If using them indoors, you have to ventilate to the outside, usually by keeping some windows open, or you'll just drive humidity up to the max and then they'll stop functioning. This does have the benefit of keeping air fresh, having a high turnover, but caps how cool they can make a structure. Air conditioners don't require this.
More maintenance. You occasionally need to replace the membrane and put something in the water to kill algae, same as a swimming pool. Don't do that, and algae will build up and it'll get a dank smell. Air conditioners just require cleaning or replacing an air filter occasionally, and if you don't do that, just become less efficient.
An evaporative cooler requires a water feed and for forced air, power. Air conditioners only require power.
They will exacerbate any humidity problems, like mold.

There are also some benefits:

For direct systems (the simplest and cheapest), where the humidified air blows at you, you get the benefits of a humidifier, like not getting chapped lips or becoming dehydrated easily. In arid and semi-arid environments where evaporative coolers work well, this is pleasant.
You can reasonably use them outdoors and in non-sealed environments like a garage. Air conditioners would be really inefficient for this.
You can easily throw essential oils in the water to get a scent diffuser.
They actually cool the air, rather than just dumping the heat somewhere else, as air conditioners do (which in cities, heats up the area around buildings).

I understand that there are also some hybrid "evaporative-assisted" air conditioners that have the air conditioner dumping heat into what amounts to an evaporative cooler. That'd get some of the efficiency benefits of an evaporative cooler without the humidity constraints.

You can find them in the hot, arid American West, where the conditions work well for them.

https://www.usgs.gov/media/images/evaporative-coolers-work-best-dry-areas-us-area-a

4 comments

What's stopping us from using similar techniques in hot climates now? Why aren't we building similar structures as homes in Phoenix instead of the standard suburban homes?
- Probably because you still need a lot of water for this to work.
  Or a clever contraption with something with a lower evaporation point and a closed loop that catches the evaporated fumes for reuse. Maybe add the ability to speed up the process with a little electricity and you've got modern AC.
- I am not an engineer, but PV-panels (or wind turbine or any other power generation system) and an AC might achieve a better result using less space?
- You can. You can get evaporative coolers (in the US, sometimes called swamp coolers). I have one. They use much less power per unit of cooling than air conditioners, but come with some drawbacks:
  You can only cool so far (well, you can build multi-stage systems to cool further, but then power efficiency drops off). Air conditioners don't have such a limitation --- throw more power at them, and they'll make air colder.
  You must have low humidity, so that the water can evaporate. At 100% relative humidity, they're totally inoperative. Air conditioners don't have this requirement.
  If using them indoors, you have to ventilate to the outside, usually by keeping some windows open, or you'll just drive humidity up to the max and then they'll stop functioning. This does have the benefit of keeping air fresh, having a high turnover, but caps how cool they can make a structure. Air conditioners don't require this.
  More maintenance. You occasionally need to replace the membrane and put something in the water to kill algae, same as a swimming pool. Don't do that, and algae will build up and it'll get a dank smell. Air conditioners just require cleaning or replacing an air filter occasionally, and if you don't do that, just become less efficient.
  An evaporative cooler requires a water feed and for forced air, power. Air conditioners only require power.
  They will exacerbate any humidity problems, like mold.
  There are also some benefits:
  For direct systems (the simplest and cheapest), where the humidified air blows at you, you get the benefits of a humidifier, like not getting chapped lips or becoming dehydrated easily. In arid and semi-arid environments where evaporative coolers work well, this is pleasant.
  You can reasonably use them outdoors and in non-sealed environments like a garage. Air conditioners would be really inefficient for this.
  You can easily throw essential oils in the water to get a scent diffuser.
  They actually cool the air, rather than just dumping the heat somewhere else, as air conditioners do (which in cities, heats up the area around buildings).
  I understand that there are also some hybrid "evaporative-assisted" air conditioners that have the air conditioner dumping heat into what amounts to an evaporative cooler. That'd get some of the efficiency benefits of an evaporative cooler without the humidity constraints.
  You can find them in the hot, arid American West, where the conditions work well for them.
  https://www.usgs.gov/media/images/evaporative-coolers-work-best-dry-areas-us-area-a