For evaporative coolers to work well, they have to constantly take dry air (outside) and add water to it through the screens, and blow it into a room.... If you put a cooler in a closed room (or one without very good external ventilation), eventually, the room's air becomes humid and it stops cooling. On mine, I had to cut holes in the walls, and put the coolers outside with the air blowing into the room (with a good place for air to excape the room also). I have problems when it rains outside on a hot day, because it barely cools anymore. Fortunately, in Vegas it only rains much a few times a year. In my new place, I got a pretty massive sized one. It is 4,500cfm sized, and the cham room is 6,750 cubic feet, so it exchanges all the room's air every minute and a half (I could pretty much have a BBQ out there and it wouldn't matter to the chameleons LOL).
Mine works excellent, yesterday my outside temps hit a high of 116 at my house, and my cham room never went above 80. Pretty good when you consider the small amount of power and a few gallons of water a day they use. Heck of alot cheaper than an A/C unit would be to run, plus they humidify the air.