Abstract: The pre-cooler includes one or more cells which are oriented about an air stream to be cooled. A housing defines a perimeter of the cell with an inlet and outlet for air passing therethrough. Water outlet nozzles within the housing are preferably supported upon bars which orient the nozzles facing in a direction counter to flow of air through the housing. Each nozzle is coupled to a separate stage with multiple stages of nozzles coupled to separate valves. A controller opens or closes different valves. The controller measures ambient humidity and temperature conditions as well as air flow rates to calculate the amount of water to be added to the air and then opens appropriate numbers of stages of valves so that an appropriate number of nozzles spray water into the air to saturate the air. Flow rate control is thus provided without pressure variations, for optimal nozzle performance.