A cooling tower is a large tower or structure that lowers the temperature of a power plant or piece of equipment. It works by cooling a water stream and then getting rid of any extra heat. Air is transporated into cooling towers via evaporation. The following is a simple formula for calculating the evaporation in a cooling tower. Take the number of gallons of circulating water per minute and multiply that by the difference between the temperature of the water in the top of the tower versus that bottom of the tower. The degrees should be in Fahrenheit. Take the sum from Step 1 and multiply it by the specific heat of water, also in Fahrenheit. Take the sum from Step 2 and divide it by the latent heat of vaporization of water. An alternative method is to subtract the blow-down from the makeup. Then, subtract the windage losses. You can get the windage losses from the manufacturer of the cooling tower.