Evaporative Air Coolers are also called Desert Coolers, Wet Air Coolers and very old ones were known as Swamp Coolers. They work using evaporation to cool the air around you and are great for hot dry days, because the only moving parts in a swamp cooler are the water pump and the fan they are almost silent to run, lightweight and portable as well. They can even be used outside for spot cooling and next to your desk in the office if you want to keep the temperature down just around you!
Evaporative coolers work by air being passed over a moist honeycombe material, the warm air from the room will evaporate the water on the honeycombe, this evaporation uses heat energy in the air - meaning the air coming out of the cooler will be colder than the air coming in.
It works a lot like when you sweat on a hot day, the water that is being perspired is being heated up by your body, when it evaporates it is taking this heat energy away from your body and into the air around you.
Water is put into the tank of the evaporative cooler, the colder the water the better it will perform (putting a couple of ice cubes in there would be a good idea). You simply then need to move it into position and plug it into a standard 13a power supply. Occasionally topping it up with water / ice