Natural Draft Cooling Towers

Natural Draft Cooling Towers

The basic mechanics of a natural draft cooling tower is this: warm air is less dense than cooler air and therefore rises in the tower and is released and pulled away, creating an upward convective movement within the structure of the tower that is a steady flow of air. Cooler air remains at the bottom, while the heat is drawn upwards. At the base of some cooling tower systems, nozzles spray mists of water into the air. As the warm, moist air rises, the cooler dry air that remains at the bottom of the cooling tower is drawn into an inlet and used in HVAC towers or for hot process cooling to replace heated air. Their water source comes from a large body of nearby water such as a lake. Sometimes referred to as hyperbolic cooling towers, natural draft tower systems are large and expensive and are most commonly used by large power companies.

As there is no need for a mechanically induced draft, there is minimal machinery maintenance required with a natural draft tower, and the cooling process will continue to function even if there is no electricity. This is a distinct advantage to using natural draft towers, and yet there are other factors to be considered. The amount of hot air removed from the tower is entirely dependent on natural factors and cannot be controlled. With a mechanically induced draft, an operator can increase the speed with which the air is moving and thus make the cooling process more efficient instead of relying on nature. There are two main types of cooling towers – cross flow towers and counter flow towers depending on the way in which the air moves and is drawn out. Natural draft towers are counter flow towers because the warm air is drawn upwards. A common design for natural draft towers is the hyperboloid shape which is important for accelerating the flow rate of the air and improving the overall efficiency of the cooling process. Towers shaped in this way use minimal materials and are structurally sound, therefore hyperbolic natural cooling towers can withstand environmental effects which may result from an exposed lifespan in harsh conditions.