Reason wrote:
....
Using a heat exchanger to reduce the humidity is a great idea, but it
wouldn't really work, because any form of air-cooling drops the air to near
or below the dewpoint anyway. That's why air-conditioners have water
drains. I've never seen an air-conditioner or a swamp cooler that could
produce low-humidity cool air.
....

Funny, I've never seen an air conditioner that didn't produce very low
RH air. In a normal air conditioner the coils are very cold, well below
the dew point, and water condenses out of the air. This cold air is
then sent into the building where it becomes very much warmer and it's
RH plummets.

Swamp coolers are another thing entirely, they work by putting water
(humidity) into the air so they can not produce low humidity air.

Anthony