The Difference Between Closed and Open Circuit Cooling Tower Systems

A cooling tower is used to cool and circulate water used in settings such as oil refineries, petrochemical and other chemical plants, thermal power stations, and HVAC systems for cooling buildings. Cooling towers extract waste heat to the atmosphere through the cooling of a water stream to a lower temperature.

There are two different types of cooling towers: closed circuit cooling towers, and open circuit cooling towers. Both types of towers serve the same purpose, but they go about cooling the water in different ways.

A direct, open circuit cooling tower is an enclosed structure that distributes warm water over a labyrinth-like packing, or fill, which provides an expanded air-water interface for heating of the air and evaporation to take place. The water is cooled as it falls through the fill, and is then collected in a cold water basin below. The heated moisture-laden air leaving the fill is discharged into the atmosphere.

A closed circuit cooling tower, or dry cooling tower, involves no contact between the air and the fluid being cooled. This tower has two separate fluid circuits, one in which the fluid is recirculated on the outside of the second circuit, which is a bundle of tubes through which the hot water is flowing. The air drawn through this cascading water provides evaporative cooling similar to an open cooling tower, except that the cooled water never makes direct contact with the air.

Closed Circuit Cooling Tower Systems

Another closed circuit cooling tower system involves a separate heat exchanger package along with an open cooling tower.  The fluid on the hot side of the heat exchanger also never makes direct contact with the air.  This allows the heat exchanger to be put inside protected from outdoor weather elements along with other system advantages.

Both open and closed circuit cooling towers are effective for cooling water, but they each work in different ways.

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