Oh, it doesn't take any skill! ^^ Just basic knowledge of chemistry.
Salt water has a lower freezing point than fresh water, so when it freezes, the ice is much colder than it would be as plain fresh water. Take this super cold ice and place it in front of a fan, and bam! Instant AC!
To make the solution, all you have to do is as a shit ton of normal table salt to water, then stick it in the freezer. You want to approach the saturation point, - ie no more salt will dissolve into the water.
Easy peasy! ^^