Indoor Swimming Pool De-humidification / Environmental Control or Air Handling as it is sometimes called is required on all Indoor pools to prevent condensation and mold forming in the environment. Due to the laws of physics enclosed air with a water source nearby has a high relative humidity. Many pool builders believe incorrectly that you can just open a few windows or doors to ventilate the room, in practice all you are doing is letting out heat to prevent evaporation and wasting the energy in cooling the pool hall down.
The underlying principal of air handling it to maintain a water temperature within 1 degree of the air temperature and thus prevent the water evaporating. We also apply hot air to cold surface such as glass to prevent condensation forming. In nature we call this a due point, as you get on a sunny morning with a cold ground temperature.
As you can see form the diagram above there is a constantly circulating system of air that is constantly being dried before being re-introduced across cold surface such as large areas of glass. On m