EVAPORATIVE cooling is energy-efficient@ environmentally?benign@ and cost-effective in many applications and all climates. Applications range from comfort cooling in residential@ agricultural@ commercial@ and institutional buildings@ to industrial applications for spot cooling in mills@ foundries@ power plants@ and other hot environments. Several types of apparatus cool by evaporating water directly in the airstream@ including (1) direct evaporative coolers@ (2) spray-filled and wetted-surface air washers@ (3) sprayed-coil units@ and (4) humidifiers. Indirect evaporative cooling equipment combines the evaporative cooling effect in a secondary airstream with a heat exchanger to produce cooling without adding moisture to the primary airstream.