A set is how many times you are going to lift and then take a break. So if you lift the weight five times, take a break, and lift again you will have done two sets. The five times would be your reps. My coaches like to write the workout like so: Squat 3x2, Bench 2x5, and so on.
Evaporative coolers use both electricity and water. How much water is used depends on the humidity of the day and the fan speed that the unit is set to operate on. A portable unit might use up to 4 litres per hour while a central system could use as much as 25 litres per hour. Ducted evaporative coolers must refresh their water supply otherwise it can become too salty, and a range of water management systems are used by different brands/models.
It is possible to have a cooling unit that does more cooling than it releases heat to the environment. The trick with indoor coolers is that the process by which they operate is not cyclic. These coolers are evaporative coolers and can also be used outside of a house to cool incoming air. They work by a similar principle as closed-loop cooler, but the fluid being used is water. The water needs to be resupplied as it evaporates.