Several types of draft cooling towers are available (but these are not dry cooling systems), including the natural draught cooling tower and the mechanical or forced (induced) draft cooling tower. The natural draught cooling tower does not use a fan to circulate the air. Instead, the heated air is sent to a chimney where pressure builds between the heated and surrounding air. The pressure is what allows the air to move from the chimney to the cooling tower. While operating costs are low due to the absence of electrical fans, a large hyperbolic tower must be built for the process to work properly. Within the category of natural draught cooling tower, there are two types of cooling tower available to the consumer. Natural draught cooling towers are available in either a rectangular timber tower or a reinforced concrete tower for the air cooled condenser in power plant operations.
Conversely to dry cooling systems, the mechanical or forced draught cooling tower uses a large fan to ensure air circulation. For power plants which run on a peak load, a high rate of cooling water is required. The fan's motor speed for this job is approximately 1000 rpm. In this type of cooling tower, the air enters a chamber and is pressurized, but instead of using the difference in air temperatures to move the air, the fan is used instead. This fan is mounted on the top of the tower. It is a popular setup in large capacity installations. The forced draught cooling tower must contain a horizontal shaft for the fan which is placed at the bottom rather than the top of the tower.
One type of cooling tower is known as the induced draft cooling tower. The process by which it operates is relatively simple. It is known as a mechanical draft cooling tower and is more efficient than a forced draft cooling tower. The induced draft cooling tower uses half as much energy in comparison to its forced draft designs. A fan mounted on the top of the assembly pulls the air through ducts called 'fills' From there the air is pulled into the cooling tower using air intake mesh.
There are a couple of options for the shape of an induced draft cooling tower. Round or square induced draft cooling towers are available to fit the needs of the air cooled condenser in powerplant operations. Water distribution is done by static branch systems or else by using a sprinkler. This type of cooling tower is easy to install and maintain, as well as making less noise compared to other types of setups. the induced draft fan motor is powered by the cooling tower motor. Its purpose is to push the draft enough that it draws outside air into the cooling tower. This takes out the steam and results in lower water temperature or 'cooling effect'.
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