Why must the doors and windows be left open ?
Because the air being pumped in Collects heat and moisture and impurities from inside the building and it must therefore be exhausted. The Evaporative Air Conditioner does NOT recalculate the inside air, and if you close the building the effectiveness of the machine will be greatly diminished and you will become very uncomfortable .

Does Evaporative Air Conditioning increase the humidity ?
In most cases, it does slightly. BUT remember that the temperature has also dropped. it is the combination of temperature and humidity that creates human comfort, and Evaporative Air Conditioners are used so widely around the world because they can create comfortable conditions. For example, 80% humidity and 30°C is very uncomfortable, but 80% humidity and 16°C is quite comfortable . Furthermore, comfort is also improved by increasing air velocity in hot conditions and Evaporative Air Conditioners create sufficient air movement to also minimize the effects
of humidity .