Cooling Towers: Behind the Screens
The cooling tower is often the forgotten component of the cooling system when it comes to maintenance. During design a tremendous effort is made to ensure that the cooling tower is unseen and unheard. As with many mechanical components, the “out of sight, out of mind” concept compliments the architecture and environment of the facility but can be the beginning of serious operational problems.
Health concerns and rising energy costs make a preventative maintenance program essential to keeping the cooling tower operation safe, efficient, and in good quality. Several simple procedures can increase safety and prevent loss of efficiency by maintaining proper water flow, airflow, and water chemistry, as well as preventing corrosion in the cooling tower.
“Health concerns and rising energy costs make a preventative maintenance program essential to keeping the cooling tower operation safe, efficient, and in good quality.”
Debris management is a significant first step in proper cooling tower maintenance. Cooling towers operate by drawing in large amounts of air through a heat transfer surface that is cooled by the distribution of water over the surface. Unfortunately, this process indirectly makes the cooling tower operate as a very large air scrubber. As the air is “scrubbed”, organic debris falls into the tower basin and begins to decompose. This creates a nutrient-rich environment for bacteria and algae growth. If not kept in check, the decomposed debris is recirculated through the tower via its spray pumps. This reduces tower efficiency and clogs the spray nozzles. The spray nozzles should be routinely checked for even spray and cleaned according to the manufacturer’s recommendations. Achieving uniform spray distribution helps optimize the tower efficiency. Also, regularly cleaning the suction strainer and flushing the basin through the tower drain will control debris and improve the tower water conditions.
A well implemented water treatment program is the second critical step in tower maintenance. Proper water treatment will control scale build-up, protect against corrosion, and control biological contaminants. Legionnaires’ disease is caused by bacteria often present in cooling towers. If untreated, the tower water could be a possible health risk to the occupants of the facility. Fortunately, a water treatment program in addition to debris management can virtually eliminate the potential risk associated with bacteria. In addition to adding the proper chemicals to the water in the cooling tower, the rate of make-up water should be adjusted to maintain proper water chemistry and prevent accumulation of impurities in the re-circulated water and tower basin. Proper operation of the water fill assembly should also be periodically checked to ensure that water is maintained at the correct level in the basin to prevent over-filling and wasteful spillage of water through the overflow.
Finally, scheduled maintenance of the tower drive system is important in maintaining efficiency and extending the life of the tower. Lubrication of the fan shaft and motor bearings should be performed regularly according to manufacturer’s recommendations. In belt-driven systems, belt tension and drive alignment should be checked monthly. Gear-driven systems should have the oil level and quality, as well as shaft alignment, checked regularly to optimize efficiency. Discharge air damper operators should be checked to ensure that the dampers are fully opening and minimizing the restriction of airflow during operation.
Advance planning and comprehensive observation can maximize efficiency, reduce health risks, and ensure that “out of sight, out of mind” does not define the standard for your maintenance program.
– Timothy J. Scharf, PE, LEED AP
Tim is a Principal, Licensed Mechanical Engineer, and LEED Accredited Professional. Please feel free to contact Tim for further details regarding the above information.
