Cooling towers are the most energy-efficient method available to reject heat from a building’s air conditioning system, but they are also the most maintenance-intensive option. Air conditioning is a way of life now; you rarely find commercial buildings without air conditioning in the mid-Atlantic region. We use it for human comfort, to preserve products, to preserve artifact archives, and to support human health. Maintaining mechanical equipment optimizes its life and limits the system’s downtime and the associated disruptions to the commercial building’s operation.
Cooling towers come in many shapes and sizes, but all generally circulate the condenser water over a coil or fill while a fan blows air to dissipate the heat to the atmosphere. Because of the varied methods and technologies, the Cooling Technology Institute (CTI) publishes standards that cooling tower manufacturers must adhere to, such as CTI STD-201 for performance, to become CTI Certified.
There are several major cooling tower brands, and all publish documents on their websites listing recommendations for startup and maintenance. These recommendations include inspecting strainers and the water fill or coil, removing scale build-up, flushing the cold water basin to remove settled dirt and debris, verifying that the make-up water supply is functioning properly, checking the condition of the drift eliminators, inspecting the electrical and piping connections, tightening fan belts, checking the oil level and oil quality on gear drive systems, lubricating fan shaft bearings, and having the chemical treatment provider check the water quality and the proper chemical levels. At startup, check the water level as a low level can draw air into the pipe system, adjust the float if installed, check the spray nozzles for the proper spray pattern, and check the basin heater operation.
As you have probably seen in the news, cooling towers can lead to Legionella outbreaks if conditions become favorable to propagate the growth of Legionella bacteria. The Center for Design Control (CDC) lists several design and maintenance strategies to limit the risk of cooling towers dispersing Legionella, such as avoiding stagnant water, using drift eliminators, keeping towers away from building ventilation intakes and maintaining proper water treatment. ASHRAE updated their Guideline 12-2023, Managing the Risk of Legionellosis Associated with Building Water Systems, reiterating the statements about cooling tower operation and including guidance on startup. They specifically address starting up after being shut down or idle for less than 5 days, which they call a wet standby, or longer than 5 days, which they refer to as a dry standby. The procedures for cleaning and disinfection are included, as well as the criteria for additional disinfection if a Legionella sample test comes back positive.
Further, the Department of Health and Mental Hygiene for New York City (DOHMH) mandates that cooling towers be inspected and disinfected regularly due in part to prior Legionella outbreaks. The DOHMH requires sampling for the presence of Legionella bacteria at least once every 90 days and for the presence of any other bacteria once a week. The cooling tower must be cleaned and disinfected if a sampling result demonstrates microbial concentrations over their prescribed limit. DOHMH further requires cleaning and disinfection any time the cooling tower is started up and requires cleaning at least twice a year.
If you are not servicing and cleaning your cooling tower regularly, put a plan in place to start, help improve your chilled water system’s energy efficiency, and reduce the risk of having your facility end up in the news associated with the next Legionella outbreak. For more information about cooling tower maintenance, contact Douglas Barnhart, PE, at dcb@ba-inc.com or 717-845-7654.