The mechanism used to move air through a cooling tower influences cooling performance, energy consumption and operating conditions. The main airflow arrangements are induced draft, forced draft and natural draft.
Induced Draft Cooling Towers
The fan is typically positioned at the air discharge near the top of the tower. It creates pressure below ambient in the upstream section, drawing outside air through the tower.
Discharging warm, moist air upward at high velocity helps reduce recirculation—the return of exhaust air to the tower’s air inlets. However, wind, nearby structures and unsuitable placement can still cause recirculation.
Forced Draft Cooling Towers
The fan is located at the air inlet and pushes air into the tower. Positive pressure downstream of the fan drives airflow through the equipment.
Operating in the incoming ambient air, away from the warm, saturated exhaust stream, can benefit component service life. Actual lifespan also depends on materials, environmental conditions and maintenance. Lower exhaust velocities in some designs can increase susceptibility to recirculation, making inlet and discharge positioning important.
Natural Draft Cooling Towers
Natural draft towers rely on the stack effect created by the density difference between the warm, less dense air inside the tower and the surrounding air. Conventional natural draft designs do not use fans to generate airflow.
Large installations often feature hyperbolic shells. These towers can serve facilities with substantial heat loads, including nuclear and large thermal power plants. Although no fan energy is required, energy is still needed for water pumping.