oh man! I just poked ptsf@lemmy.world for a Austria!=Australia flub in another thread... my come uppins!

Practically all even semi-modern DCs are built for servers themselves to be air cooled. The air itself is cooled via a heat exchanger with a separate and isolated chiller and cooling tower. The isolated chiller is essentially the swamp cooler, but it's isolated from the servers.

There are cases where servers are directly liquid cooled, but it's mostly just the recent Nvidia GPUs and niche things like high-frequency-trading and crypto ASICs.

All this said... For the longest time I water cooled my home lab's compute server because I thought it was necessary to reduce noise. But, with proper airflow and a good tower cooler, you can get basically just as quiet. All without the maintenance and risk of water, pumps, tubing, etc.

yes. I programmed and integrated swap coolers at Amazon data centers. when the cool air hits the hot aisles the humidity goes down.

Industrial cooling towers are usually evaporative in my experience, smaller ones are large fans moving air over a stack of slats that the return water is sprayed or piped over and the collects in well for recirculation, larger ones afaik (like what you'd see at power plants) operate the same idea. Top ups and water chemistry is all automated.

Those systems have operation wide cooling loops that individual pieces of equipment tap into, some stuff uses it directly (see that with things like industrial furnaces) but smaller stuff or stuff that's sensitive you'll see heat exchangers and even then the server & PLC rooms were all air cooled, the air cons for them were all tied into the cooling water loops though.

From a maintenance POV though, way easier to air cool, totally seen motor drive racks with failed cooling fans that have had really powerful external blowers rigged up to keep them going to the next maintenance window. Yeah, industrial POV but similar idea.