Below about 5,000 ft, you can expect the temp below ground to average between 45 and 65 degrees, depending on location. The lava tubes around Mt. Adams and Mt. St. Helens average around 45 degrees most of the year, although there is at least one cave that maintains ice in it the whole year. Likewise, I think the big hole in South Dakota is a little bit warmer, but then it breathes a lot more than the lava tubes. IIRC, Carlsbad and Mammoth maintain about 65 ambient pretty much the whole year. The government used to store cheese and butter in some of the caves around Mt. Adams, thus some were named the "Cheese" and "Butter" cave systems. As a whole, I found the lava tubes far too humid even at the lower temps, considering you don't go in them without at least a hard hat, coveralls, boots and gloves.

Bike week is early enough in the year (still winter here) that evaporative cooling will still kinda work, especially if you have a big enough air flow, so long as it doesn't rain. Right now, a swamp cooler in central Florida would be fairly worthless. You'd be better off with just a fan. IIRC the air chillers in Pensacola at NTTC Corry Station used an open water circuit on the exchanger elements, but that had more to do with improving thermal conductance to ambient I think than with evaporative cooling. It wasn't the heat of vaporization that was being utilized so much as the fact that water flowing over a surface makes a much better thermocouple.

Any gas that can be condensed into a liquid can be used as a refrigerant. Ammonia is one of those who's temp range is more suited to refrigeration applications, in that the pressure vessel required need not be so robust.

It seems counter-intuitive that by the application of heat, you can actually cool a volume of air.
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The ultimate result of shielding men from the effects of folly is to fill the world with fools.
-- Herbert Spencer, English Philosopher (1820-1903)