They would hang wet sheets inside the screened panes, and as the warm air passed through the screen, it would be cooled by the wet sheets. That cooler air would circulate slowly, cooling the sleeping area and easing the suffering that summer nights could cause.
The Today's Coolers Technology
Today we have the technology to cool our indoors sleeping and living quarters much more effectively, but one of these technologies, the air cooler, works very effectively on a similar principle as the one employed by those earlier cooing attempts.
Different types of evaporative coolers
Evaporation happens in nature all the time. It is the way that our bodies cool themselves by the process of sweat evaporating off of the skin. You’ll notice the effects of natural evaporative cooling near bodies of water as a cool breeze comes off the water, especially in areas with hotter, drier air.
As the dry air passes over the water, the air will absorb some of the water and become cooler because heat naturally tries to equalize itself. Meaning that when a hotter and cooler material intersect, the nature of thermodynamics is that the 2 materials will transfer heat until they are the same temperature.
So as the air meets the water, some of the heat moves from the hotter air to the cooler water, leaving the evaporative cooler than it was. A cooler simply puts this natural event to regular use in a machine that will efficiently and effectively cool your home or office.
Main Manufacturers or Distributors
But an evaporative cooler doesn’t just cool the air, it also moves it through the room with a fan or blowing system. The cooler pulls fresh hot air from outside through moist pads so that it can pick up water and be cooled by as much as 30 degrees. The pads also have the added advantage of acting as an air purifier or ionizer. That cooler, cleaner air is then blown throughout the room or the building.
Because the cooler has to have dry air in order to pick up water and be cooled, evaporative coolers work best in 
dry, hot climates. But where they do work, they can be much more cost effective than regular air conditioners or other cooling home appliances. Not to mention the fact that they are also better for the environment. You can even find solar-powered evaporative coolers for the truly environmentally concerned.
There are sizes with air speeds available for every need, from portable window coolers to high-powered industrial coolers for commercial use. Whatever the need, there is an evaporative cooler to meet it.
