Comparing Cooling Towers and Dry Coolers
Evaporative cooling towers are one of the best long-term solutions for industrial cooling challenges. They offer advantages when compared to a dry cooler, notes one manufacturer. In a white paper, Gary Dicker, the director of DHD Cooling, offers his view on the two cooling technologies.
Cooling towers exchange the heat contained in the circulating water by spreading out the water over a large surface area and bringing air into contact with the surface of the water. The volume of water passed over the cooling tower is always much greater than the amount of evaporation that occurs, which is typically about 1.6 percent of the circulating flow. So, the opportunity for impurities to build up is reduced because the water has a constant washing affect. Couple this with the fact that fouling of the heat exchange surface does not significantly reduce the surface area of the water until it is very severe, and you have a heat exchanger that maintains its performance for much longer than a dry cooler.
With dry and hybrid coolers, the air coolers rely on passing large volumes of ambient air over a finned coil. In some circumstances, the air local to an air cooler can be influenced by other plant, or even the equipment itself, resulting in even higher inlet air temperatures. To achieve colder water temperatures, there are various methods of wetting the finned coils, or increasing the moisture content of the air. This will bring the air temperature down, which will reduce the inlet air temperature and improve performance. Many of these methods can result in the coil surface becoming wet for long periods which can help to adhere impurities in the air to the coil fins. Finned coils need regular cleaning, but they are hard to clean due to the trade-off between the water pressures needed to clean the coils versus the potential to fold the fins during cleaning.
Also, Dicker notes, one of the least-expensive components in a cooling tower is the fill pack (heat exchange surface), which is designed to be removed and replaced. Compare this to a dry cooler, where a coil serves as the heat exchange service and can be expensive and difficult part to remove and replace.
The ability to withstand freezing temperatures is another difference between the two cooling systems. Freezing the coils in a dry cooler can be catastrophic, crippling plants in a matter of hours. While cooling towers also can freeze, they often require little or no thought throughout the winter months.
And perhaps most importantly, cooling towers achieve the lowest cold water temperatures compared to dry and hybrid coolers, which can directly affect your productivity.
DHD Cooling maintains cooling towers that are 40 years old, and they still deliver the same cold water temperature that they did 40 years ago (providing the fill is clean and the air moving equipment and water distribution systems are working). Regular cleaning is simple to undertake, and replacement of the main components is also relatively easy.