The cooling tower rejects waste heat contained in circulating cooling water utility to the atmosphere. They can be classified by the type of draft either mechanical or natural; by the way air and water flow, either crossflow or counterflow; and heat transfer mode, evaporative also known as wet, or dry. The conventional industrial cooling towers are mainly wet or evaporating ones, and for economical reasons, tend to have mechanical draft. The evaporative heat transfer process, implies high water losses, demanding constant make-up.
An industrial cooling tower is normally constructed in cell sections, each one being an almost independent tower, although sharing the same water treatment, but with separate circulation pumps and fans.
Water cooling process efficiency is greatly dependent on ambient conditions and heat rejection load. Other factors influence efficiency like heat transfer surface area, contact time between water and air streams, and air-to-water flow ratio. These factors must be balanced to select the best cooling tower for the design conditions.
Energy efficiency opportunities in water cooling units begin with selection of the appropriate cooling tower, considering site average atmospheric conditions. Selection of fillings influences air pressure drop, fan selection and sizing. Attaining cooling water quality to design conditions avoids surpassing the expected flow rate of circulating water and prevents additional tower cells being used in a certain process condition. This reduces supplementary energy consumption in pumping, besides leaving room for additional cooling demands. Staging or using variable speed drives for tower fans and water pumps is another option, especially if the tower has many cells. Turning off unnecessary cells momentarily should be considered.
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