Passive evaporative cooling has great potential as an alternative to conventional air-conditioning in and hot climates because of its low cost and zero pollution. This paper describes a novel evaporative cooling system with an automatic wind-tracking device to improve its operating efficiency. The design and operating principles are discussed. A mathematical model is simplified by the assumption of convective heat and mass transfer of staggered streamlets of water. A computer program has been developed to calculate the deflection and length of spray water streamlets, as well as evaporative water mass, minimum cooled water temperature and required cooling time. A typical example illustrates that approximately 20 kg water are evaporated and around 26 min are required for 980 kg of water to be cooled from 28 degrees C to the wet bulb temperature of 19.2 degrees C of ambient air in a typical and hot climate (relative humidity = 0.30, dry bulb temperature = 32 degrees C and wind velocity = 4 m s(-1)). The application of adsorbents, would allow the evaporative cooling system to be applied in hot, humid climates, in addition to hot climates with low humidity. Copyright (c) 2006 John Wiley & Sons, Ltd.