How does ASHRAE recommend cooling towers be cleaned to avoid Legionellosis?

ASHRAE Recommendations Cooling Tower Legionella CES.jpgASHRAE's recommendations regarding Legionellosis are contained in ASHRAE Standard 188-2015, Legionellosis: Risk Management for Building Water Systems, and the ASHRAE Guideline 12 -2000, Minimizing the Risk of Legionellosis Associated with Building Water Systems.

ASHRAE recommends that cooling towers should be designed, installed, operated, and maintained in accordance with ASHRAE Guideline 12 -2000 to minimize the risk of dissemination of legionella bacteria. The guideline includes recommendations for cleaning and disinfection.


Recommended treatment for Cooling Towers including fluid coolers and evaporative condensers:

  1. System be maintained clean
  2. A biocidal treatment program be used
  3. Qualified water treatment specialist services

CDC Legionella Toolkit 


System Maintenance:

  • Regular visual inspections should be made for cleanliness
  • Cold water basin should be cleaned when any dirt, organ matter, or debris is observed or found through sampling
  • Drift eliminators should be inspected regularly and cleaned if required or replaced if deteriorated or damaged

Cooling Tower System Shutdown and Start-up

  • When the system is shut down for more than a period of three days it is recommended that the entire system be drained to waste.
  • When draining is not practical for short shutdowns, the stagnant cooling water must be pre-treated with the appropriate biocide regimen before start-up.

Monitoring for Legionella

Culturing of Legionella may be appropriate if done for a appropriate reasons:

  1. Verifying the effectiveness of a water treatment protocol
  2. Tracing the source of an outbreak
  3. Evaluating the potential amplification/transmission sources at a facility
  4. Verifying that the decontamination treatment procedures have been effective
  5. Caring for people in Health Care facilities with exceedingly high risk for developing Legionnaire's Disease.
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Refer to the equipment manufacturer’s operation and maintenance instructions for guidance on cleaning, suggested frequency of inspection and cleaning for various components, and recommendations for cleaning prior to initial and seasonal start-up.

ASHRAE Pubs referenced herein:

  1. ASHRAE Standard 188-2015, Legionellosis: Risk Management for Building Water Systems
  2. ASHRAE Guideline 12 -2000, Minimizing the Risk of Legionellosis Associated with Building Water System

Additional Resources:

  1. Prevention of Legionellosis for Facility Managers
  2. Are You Compliant with 2015 ASHRAE Standards on Preventing Legionellosis?

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Posted by Comprehensive Energy Services

Comprehensive Energy Services, Inc. is an award-winning, self performing provider and recognized leader in Design Build and Maintain Mechanical Contracting and Plumbing; providing a full range of advanced HVAC commercial, healthcare, and industrial services, including mechanical engineering design, mechanical construction, plumbing, IAQ, preventative maintenance and system maintenance throughout Florida.

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