ENTHALPY EXCHANGE VISUALIZED To understand the exchange of total heat that takes place in a cooling tower, let’s assume a tower designed to cool 120 gpm (1000 lb/min) of water from 85°F to 70°F at a design wet-bulb temperature of 65°F and (for purposes of illustration only) a coincident dry-bulb temperature of 78°F. (These air conditions are defined as point 1 on Figure 2) Let’s also assume that air is caused to move through the tower at the rate of 1000 lb/ min (approximately 13,500 cfm). Since the mass flows of air and water are equal, one pound of air can be said to contact one pound of water and the psychrometric path of one such pound of air has been traced on Figure 2 as it moves through the tower.