“Natural Draft Cooling Towers” Natural contacts ambient air rising up through the tower either by forced draft using large fans in the tower. Natural draft is utilizes a tall chimney. Warm, moist air naturally rises due to the density differential compared to the dry, cooler outside air. Warm moist air is less dense than drier air at the same pressure. This moist air buoyancy produces an upwards, current of air through the tower.Natural that appears like a natural draft setup, though airflow is assisted by a fan.This association is misleading, as the same kind of cooling towers are often used at large coal-fired power plants as well. Conversely, not all nuclear power plants have cooling towers, and some instead cool their heat exchangers with lake, river or ocean water. 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. Natural cooling towers have become the design standard for all natural-draft cooling towers because of their structural strength and minimum usage of material. The hyperboloid shape also aids in accelerating the upward convective air flow, improving cooling efficiency. These designs are popularly associated with nuclear power plants. That contact causes a small amount of the water to be lost as windage (W) and some of the water to evaporate.