The larger the physical size of the cooling tower, the more energy efficient it is. The least efficient are the forced draft units. Look at the various designs also from Marley and Baltimore Aircoil. They all work by rejecting the heat of the condenser water to the air by evaporation. The water is distributed equally to the cooling tower fill so it gets in intimate contact with the air either forced by the fan (blown through the fill) or induced draft (drawn through the fill by fan suction). Air can pass crossflow or counterflow to the fill with respect to the water flow. Along with evaporation, there is water lost to drift & some water must be bleed off under the water treatment program so as not to exceed the design concentration cycle. Typical total water makeup required for evaporation, drift & bleed is 0.05 gpm/ton. The heat evaporated is equal to the cooling tons + the compressor input. This is about 15000 Btu/hr. Figure latent heat of evaporation at about 970 Btu/lb, 62.34 lb/cubic, 7.481 gal/cubic ft & 60 minutes per hour, you get 0.03 gpm per ton for evaporation.