Over the years, traditional wisdom has supported the idea of a water body such as pond, lake or a fountain to provide cooling effect to the surrounding environment. This effect lowers the indoor air temperature – a widely known concept of evaporative cooling. This phenomenon is largely witnessed in systems such as desert coolers in most Indian households.
Evaporative cooling lowers the indoor air temperature thus lowers the energy cost for air-conditioning in buildings. Reduced energy load contributes towards meeting the NZEB design goals. However, evaporative cooling is mostly effective in hot and dry climate where the humidity is low.
Air is in direct contact with the cooling media, water, in direct evaporative cooling. The most commonly used methods are water bodies and water sprays.
Passive downdraught towers catch hot ambient air through wind scoops at the top. This air is cooled either through mechanical systems like nozzle sprays or through passive systems like water filled vessels. The heavy cool air sinks to the bottom zone of habitable spaces. Efficiency depends on the temperature differential between the warm outside air and cool air inside the tower.
Publications
Evaporative coolers can replace mechanical cooling in hot-dry climates. In composite climates evaporative cooling systems can be used to reduce HVAC system use during early summer months when the temperatures are high and humidity is low.
It has been calculated that temperature of 1 M3 of air will be reduced by 1° centigrade by the evaporation of 0-5 gm of water.