The present invention relates to a system and method of cooling by latent energy transfer and, in particular, to cool a fluid by discharging unwanted low temperature thermal energy to a surrounding ambient environment utilizing a fluid evaporation process involving permitted or forced ventilation of air across a surface area of a heat transfer fluid. The invention further relates to an air treatment system utilizing the cooled heat transfer fluid for cooling air and for supplying ventilation air to the evaporation process. A body of liquid is cooled close to the prevailing wet bulb temperature, discharging unwanted thermal energy to the surroundings, rendering the liquid suitable as a cooling medium for removing unwanted thermal energy from a location or in a process.