Cooling Towers

Conservation of energy says that energy cannot be destroyed, yet many people never stop to think Cooling Towerabout what happens to the energy removed from a home or office by the air conditioner.  Cooling towers (shown to the right) are one device used throughout the industry to reject this waste heat to the environment. There are two basic types of cooling towers: the indirect (closed) and direct (open) style. Indirect (closed) cooling towers have the cooling water circulate through tubes within the tower where it is cooled by the air through convection from the pipes. The direct (open) cooling towers, on the other hand, have the cooling water mixed with air within the tower and cooled by a psychrometric process.

Cooling Tower Schematic [6]

Open cooling towers are made in crossflow and counterflow designs. The orientation of a crossflow cooling tower has the water running down and air flowing perpendicular to the water causing evaporation. A counterflow type consists of water flowing down and air flowing parallel in the opposite direction. In both cases as water is evaporated energy and moisture are added to the air. The resulting air-water vapor mixture (and the energy it holds) is then carried away from the cooling tower by air circulation. On cold, wet days the cooling tower will appear to be emitting smoke, which is a large

misconception. What is actually being seen is condensed water vapor leaving the tower. In other words, it’s a cloud machine! The cooling towers on campus are of the crossflow type. They reject the waste heat that is collected from the air conditioning processes across the entire campus. View the video below to get a better perspective of the cooling towers.

Cooling Tower Walkthrough Video

Types of Cooling Towers

Cooling towers also have different designs for water distribution. The two types of distribution are gravity and spray. Gravity distribution is used by crossflow cooling towers and consists of a hot water basin above the wet deck and metering orifices at the bottom of each basin. A wet deck is a series of cascading metal sheets Wet Deckthat water will flow over to increase the cooling rate by increasing the exposed surface area. The water flowing over the wet deck can be seen to the right (a picture of the wet deck is shown above). What you are seeing is the front of the cooling tower shown in the picture to the above left. The metered orifices distribute the water according to depth in the water basin. These systems can be inspected while in operation and require low pump head. Spray distributors are used on counterflow cooling towers and use spray nozzles mounted on pipes suspended above the wet deck.