(see diagram at left). Air flow first enters an open area beneath the fill media, and is then drawn up vertically. The water is sprayed through pressurized nozzles near the top of the tower, and then flows downward through the fill, opposite to the air flow. Advantages of the counterflow design: Spray water distribution makes the tower more freeze-resistant. Breakup of water in spray makes heat transfer more efficient. Disadvantages of the counterflow design: Typically higher initial and long-term cost, primarily due to pump requirements. Difficult to use variable water flow, as spray characteristics may be negatively affected. Typically noisier, due to the greater water fall height from the bottom of the fill into the cold water basin Common aspects Common aspects of both designs: The interactions of the air and water flow allow a partial equalization of temperature, and evaporation of water. The air, now saturated with water vapor, is discharged from the top of the cooling tower. A "collection basin" or "cold water basin" is used to collect and contain the cooled water after its interaction with the air flow. Both crossflow and counterflow designs can be used in natural draft and in mechanical draft cooling towers. Wet cooling tower material balance Quantitatively, the material balance around a wet, evaporative cooling tower system is governed by the operational variables of make-up volumetric flow rate, evaporation and windage losses, draw-off rate, and the concentration cycles. In the adjacent diagram, water pumped from the tower basin is the cooling water routed through the process coolers and condensers in an industrial facility. The cool water absorbs heat from the hot process streams which need to be cooled or condensed, and the absorbed heat warms the circulating water (C). The warm water returns to the top of the cooling tower and trickles downward over the fill material inside the tower. As it trickles down, it contacts ambient air rising up through the tower either by natural draft or by forced draft using large fans in the tower. That contact causes a small amount of the water to be lost as windage or drift (W) and some of the water (E) to evaporate. The heat required to evaporate the water is derived from the water itself, which cools the water back to the original basin water temperature and the water is then ready to recirculate. The evaporated water leaves its dissolved salts behind