Seasonal cooling towers across the nation are started up each Spring. It is crucial that cooling towers are cleaned and sanitized every year for both operation efficiency and for public health protection.
Cooling Towers produce ideal conditions for Legionella bacteria growth and aerosolization.1 The location of cooling towers is often proximal to direct sunlight which, combined with the warm tower water, causes slime and biofilm to grow. Slime and biofilm act as a protective barrier for Legionella bacteria, allowing the bacteria to amplify. Often installed on open rooftops, cooling towers are also susceptible to windblown debris. This debris can offer nutrients to the bacteria, further enabling Legionella bacteria to grow. Cooling towers emit water vapor drift in plumes that, depending on the size and location of the tower, can travel over wide geographical areas. If towers are not cleaned regularly, the odds increase that the water vapor will contain Legionella bacteria, possibly affecting a large number of people.2
The second reason cooling towers must be cleaned is that if not done regularly, cooling towers decrease their operational efficiency. Efficient cooling towers use the least amount of water as possible to maintain its cooling processes, saving the facility money. Maximizing the number of water cycles through the cooling tower system will increase the tower’s productivity by minimizing blowdown water quantity and reducing make-up water demand. However, while more water cycles are good for water conservation, it can lead to increased scale build up on tower components. This can decrease heat transfer ability and cause downtime and corrosion problems.3 It is important to remove this scale with regular cleaning to ensure that cooling towers operated properly and efficiently. Per the recently updated, ASHRAE Guideline 12-2020-Managing the Risk of Legionellosis Associated with Building Water Systems, an annual off-line cleaning and disinfection is recommended as a minimum frequency.4
Don’t forget! New York State Department of Health requires all cooling towers to be cleaned prior to start-up if the system has been shut down for ≥5 days. Even more stringently, New York City Department of Health and Mental Hygiene requires that all cooling towers be cleaned no less than two times each year.
1. OSHA. Control and Prevention. https://www.osha.gov/SLTC/legionnairesdisease/control_prevention.html#hotwater . Legionellosis (Legionnaires’ Disease and Pontiac Fever). Accessed February 11, 2019.
2. Nygard K, Werner-Johansen O, Ronsen S, et al.An outbreak of Legionnaires’ disease caused by long-distance spread from an industrial air scrubber in Sarpsborg, Norway. Clin Infect Diseases.46(11);2008:61-69.
3. Office of Efficiency and Renewable Energy.Best Management Practice #10: Cooling Tower Management.Federal Energy Management Program. https://www.energy.gov/eere/femp/best-management-practice-10-cooling-tower-management. Accessed February 12, 2019.
4. ASHRAE. (2020). Guideline 12-2020 — Managing the Risk of Legionellosis Associated with Building Water Systems . Retrieved from https://www.techstreet.com/ashrae/standards/guideline-12-2020-managing-the-risk-of-legionellosis-associated-with-building-water-systems?product_id=2111422#product