COOLING TOWER | Inspecting & Cleaning Overview

November 16, 2022 |

There are 4 reasons to ensure your evaporative cooling tower is regularly inspected and cleaned:

  • To meet local / country codes and regulations [Legionella]
  • Manufacturers requirements [to ensure performance]
  • To control corrosion within the tower and system components
  • To ensure the equipment is operating as efficiently as possible

Please note that the following, like all information, is provided from our experience and research. As each tower and location could be different, you should not fully rely on it and ensure to conduct your own investigations as to the expectations and needs for your project. 

For our article on which Maintenace Checks should be conducted see our article on ‘What to do | Cooling Tower Preventative Maintenance Inspections

Table of Contents

Local / Country Codes and Regulations

Across the world, governments have required that a building owner who has any type of evaporative cooling system [for example, cooling towers] on their premises can clearly and easily prove that the systems are regularly cleaned and maintained. 

This is due to the increase in issues relating to Legionella and its impact on health and tracing the outbreak if it occurs.

New York City Local Law 77-2015 [USA]

For example under the New York City Local Law, 77 [2015] requires the building owner to register with the city, inspects, cleans, disinfects, and tests their cooling tower annually, certifying that they comply with the law.

Building owners are also obligated to create routine and long-term maintenance procedures for the equipment.

United Kingdom ‘Health and Safety at Work Act 1974, the Control of Substances Hazardous to Health

Under the above, there is a document HSG274 Part 1 Legionnaires’ disease: The control of Legionella bacteria in evaporative cooling systems that details the requirements for ‘duty holders,’ which covers employers and those in control of premises stipulating what their responsibilities are relating to Evaporative Cooling Systems, similar to the New York City Law above.

Under the document, there is a section called ‘Cleaning and Disinfection’ for advice on the cleaning requirements. There is also a section on the Legionella Risk assessment that should be completed with documents being updated and maintained regularly.

We have written more about the cooling tower maintenance requirements in our article ‘….’


How often should a cooling tower / cooling system be cleaned

Each installation and site location is different, but the best way to understand the frequency needed is based on previous inspection results and observations.

If the existing system is noted to have a good chemical treatment regime, clean ambient environment, clean process environment, and be free of fouling, then inspections would be conducted at less frequency than those systems where fouling is noted, meaning more regular cleaning.

If the installation is new and has no history to review, then we would suggest using your experience or the knowledge of someone with experience and starting with more frequent inspection and cleans.

Over time, if it is found that the fouling is not a problem, then reduce the frequency until having a nice balance of inspection vs. fouling being noted.

Referring to the HSE, they note 2 examples of how regularly a cooling tower should be inspected and cleaned, the information is provided as typical but not prescriptive:

  • Immediately before the system is first commissioned.
  • after any prolonged shutdown of a month or longer.
  • from any observations or suggestions of any regular inspections that are completed.
  • if the cooling tower system/pipework has been modified or altered, this includes any replacement of equipment such as pumps or chillers.
  • Every 3 months – Cooling Towers installed into a ‘dirty’ process and or ambient environment [industrial].
  • Every 6 months – Cooling Towers being part of a condenser system serving comfort cooling [office cooling]
  • Every 12 months – Cooling Towers installed in an extremely ‘clean’ process and or ambient environment [in a nice green field].

In addition to the above, the manufacturer’s maintenance manuals should also be referred to, as these can require a dedicated cleaning programme for the tower.


Steps required to clean the tower

To ensure the engineers are safe and the tower is cleaned correctly, the following will be covered:

  • Understanding what type of tower is installed
  • Documentation needed to complete the works
  • Personal protective equipment [PPE]
  • Tools and items required to complete the works
  • Pre-cleaning inspection
  • Cooling tower cleaning procedure/process
  • Reporting 

Understanding what tower is installed

Different types of towers will require a slightly different method of cleaning. 

Refer to our article ‘Quick Guide | Types of Cooling Towers and Ponds‘ to understand what type you have [counterflow/crossflow].


Documentation to complete the works

The following documentation should be written and approved before starting the works:

  • Risk assessment for the works
  • Method statement for the works
  • Drawings [schematic/layout]
  • COSHH assessment the works
  • Permit for the works
  • Discharge license
  • Cleaning checklist

Personal Protective Equipment [PPE]

For the engineers and operatives involved in this work, PPE is essential as there are various types of hazards. The following should be used and worn:

  • Hard Hat – to protect from bumping and hitting head.
  • High Visability Vest – Usually a site requirement for identification and to be able to see in low light conditions.
  • Eye protection – to protect from water and water droplets entering the eyes.
  • Face mask/respiratory protection, rated to correctly for the works – to protect from breathing in water vapor and droplets.
  • Overalls/Long Trousers/Long Sleeve Shirt – to protect skin and clothing
  • Gloves, rated correctly – to protect the hands from cuts, abrasions, and chemicals.
  • Steel toe-capped boots – to protect feet
  • Safety Harness and Fall Arrest – for works at high level

Cooling Tower Cleaning Equipment Required

To complete the cleaning successfully, the following cooling tower cleaning equipment and tools will be needed:

  • Access Equipment
  • Trolley
  • General Handtools
  • Water quality testing equipment [bottles/portable testing kit]
  • Flexible Hoses
  • Filtering System
  • Wet Vacuum
  • Jet Washer
  • Sump Pump
  • Cloths and Rags
  • Chemicals

Goodway sells a Cooling Tower Cleaning Kit that is a great way of getting what you need.

Access Equipment

Access equipment will usually be required, if not provided permanently at the cooling tower for access to and around the unit.

This equipment can consist of:

  • Ladders
  • Access Platforms
  • Elevated Working Platforms

Trolley

A trolley can help move the equipment and materials needed to complete the cleaning, from where there are stored to the working area/tower location.

General Handtools

General hand tools such as screwdrivers, hammer, cable ties, knives, etc.

Water quality testing equipment [bottles/portable testing kit]

To enable the water testing to be completed onsite and in the laboratory, a site testing kit including clean bottles will be used.

Flexible Hoses

Temporary hoses will be needed to connect the cooling tower basin to the building drainage, allowing the dirty water to be discharged.

Hoses will also be needed to connect any filtration devices used etc.

Filtering Systems

Using a filtration system installed to recirculate the water from the dirty cleaning process, through filters, and back into the basin clean.

This can help save a considerable amount of water from being discharged to drain.

The system will usually be portable and can be backflushed to drain once the strainers become clogged.

Wet Vacuum / Sump Vacuum Cleaner

A wet vacuum or similar type would be used to help clean and remove the sludge and debris from the basin and collecting for later removal and discharge.

Jet / Pressure Washer

The jet washer would help clean the internals of the tower, the basin, drift eliminators, and fill material.

Sump Pump

Generally, the tower will have a drain used to remove the water from the tower. A sump pump can be useful if the tower does not fully drain.

Cloths and Rags

Used to help clean the tower and its components.

Chemicals

Speak to your chemical specialist to help select the correct cooling tower cleaning chemicals, as qualified advice would be needed for each project. Below are a few that would generally be 

  • Descaler [Hydrochloric Acid]
  • Fill Cleaner
  • Biospray 
  • Chlorine Dioxide 

Cooling Tower Pre-Cleaning Inspection

As noted above, regular inspections should be completed, and below we will run through how the ‘pre-cleaning inspection can be completed. Again, like with anything Cooling Towers, refer to your local code/regulation requirements to ensure what is needed where your towers are installed.

Completing a thorough and detailed inspection will ensure the following:

  • Water treatment is effective – although we can’t fully rely on the chemicals that are injected into the condenser water system to fully control the fouling of the tower and its surfaces, the chemicals will slow it down. If the fouling is becoming more regular, it may point towards a problem with the chemical levels or what is being used.
  • Cleanliness of System – a visual inspection and some testing of water quality will quickly highlight any issues that are lurking in the system.
  • What type of cleaning will be required – sometimes it’s just a quick clean, and other times it’s a deep clean. The inspection would point towards which cleaning method would be applicable.
  • Meet codes and regulations – detailed inspections are usually required as part of local codes and regulations. Completing and documenting the inspection will help achieve this.

Sequence for Inspection and Cleaning

Note that any works associated with the maintenance and checks of the cooling tower/condenser system should be conducted by a person who is competent, experienced, and qualified.

Ensure that the local requirements are fully investigated and understood, as they vary from location to location.

Step 1: Ensure the documentation is in place

All documentation should be in place and available before the works commence. The below provides a guide of what would generally be needed:

  • Risk assessments
  • Method Statements
  • Drawings [schematic/layout]
  • COSHH data sheets
  • Previous maintenance records [this is to review and see any common issues occurring]
  • Water treatment service report [this is to review the current water quality analysis is inline with requirements, quality of water, and frequency of sampling/testing].
  • Permit works
  • Discharge licenses
  • Cleaning checklist

Step 2: Inspect and understand the system

Using the drawings, review the system to ensure understanding of the following:

  • its design
  • number of cooling towers and configuration
  • layout
  • pumps
  • chillers
  • valve configurations
  • drain/sampling points
  • pipework connections/balance pipes
  • electrical supplies
  • filtration systems
  • chemical treatment systems/dosing locations and delivery method
  • water quality monitoring system
  • make-up water supply
  • utility water supply
  • storage tanks

Step 3: Ensure all tools and equipment/PPE are available

Within the method statement, there will be a list of the tools and equipment needed to complete the tasks. We have noted some of these above under the section  “Personal Protective Equipment & “Tools and items required.”

Ensure all items are available as per the evaluation, method statement, risk assessment, and COSHH datasheets.

Step 4: Write a description of the system and its operation

Within the records for the works that are being conducted, there should be a fully detailed explanation of how the system is currently operating by using words and or marked-up drawings.

Initially, this will allow for any immediate issues and problems to be highlighted.

Step 5: Review Water Treatment Service Reports

A review of the water treatment service reports should be conducted to ensure that the works have been completed throughout the year.

The reports will prove that the make-up and cooling water has been regularly inspected, sampled, tested, and analyzed, ensuring it is of the correct quality for the system and that no underlying issues or more frequent testing should be conducted.

Below is a table from the HSE guideline:

RefParameterMakeup Water SystemCooling Water SystemNotes
1Calcium or Total Hardness
[mg/l CaCOȝ]
MonthlyMonthly 
2Total Alkalinity
[mg/l CaCOȝ]
QuarterlyMonthly 
3Conductivity [µS/cm]
or
Total Dissolved Solids [mg/l]
MonthyWeekly 
4pHQuarterlyWeekly 
5Inhibitor Level
[mg/l]
n/aMonthly 
6Oxidising Biocide
[mg/l]
n/aWeekly 
7Microbial Activity
[cfu/ml]
QuarterlyMonthly 
8Legionella Analysisn/aQuarterlyBS 7592 Sampling for Legionella bacteria in water systems. Code of practice
9Total Iron
[mg/l Fe]
QuarterlyMonthly 
10Chloride
[mg/l Cl]
MonthlyMonthly 
11Concentration Factor
[calculated value]
n/aMonthly 
12Calcium Balance
[calculated value]
n/aMonthly 

The following equipment should be used to understand the water quality:

  • Send samples to the laboratory
  • Dip Slides
  • Incubator
  • Colorimeter

Click here to see the tools and how results should be interpreted. Location and timing of sampling.

Sampling would usually be conducted at the return pipework to the cooling tower away from the dosing system. If possible, each test should be conducted at the same time of day to ensure the dosing/chemicals in the system are not affecting the results.

Step 6: Complete the pre-clean inspection

Inspect the installation focusing on the following areas around and within the tower for fouling:

RefDescriptionSystem StatusFocus on
1Review General System ConditionOn/Off1. Damage to protective finishes
2. Scaling and corrosion
3. Biofilm and fouling occurring on wetted surfaces
4. Build-up of dirt and debris
2Internal Surfaces, Structure, and SupportsOff1. Corrosion
2. Damage
3. Build-up of deposits
3Water Distribution SystemOn/Off1. Nozzles and/or hot water basin debris
2. Water distribution
3. Damage
4. Leakage
5. Corrosion
4Fill Pack
[this will usually require the whole pack to be removed or use a camera]
On/Off1. Fill pack debris and scaling
2. Water distribution through the pack
3. Damage
4. Leakage
5. Corrosion
6. Installed correctly [orientation]
5Drift Eliminators
[where possible remove for inspection]
Off1. Debris and scaling
2. Distribution through the Eliminators
3. Damage
4. Leakage
5. Corrosion
6. Installed correctly [orientation]
6BasinOff1. Basin debris and build-up of deposits
2. Biofouling/organic material
3. Water distribution and flow to the condenser system
4. Damage
5. Leakage
6. Corrosion
7. Pipework connections
8. Anti-vortex guard
7Sweeper/Filtration Systems
[including pumps etc.]
On/Off1. Corrosion
2. Damage
3. Build-up of deposits
8Chemical Dosing System
[including all pumps etc.]
On1. Corrosion
2. Damage
3. Dosing is sufficient
4. Storage of chemicals safe
5. Chemical correct
9Bleed-Off SystemOn1. Corrosion
2. Damage
3. Operating as per design

If it is seen that the system and components are heavily contaminated and fouled, especially the basin and tower fill pack, then this could also affect the other items in the system such as pipework, pumps, chillers, and strainers.

These should also be inspected if there is a concern and evaluated if further works would be needed. 

All findings should be clearly documented and remedial actions recorded.

Step 7: Cleaning Process

Once the pre-clean inspection has been completed and based upon the findings, the next stage will be to define the cleaning process to remove each issue and clean the tower.

This will vary depending upon what is found and how much is seen.

The below provides some examples of the steps to take:

RefObservationImpactAction
1Damage to protective finishesAcceleration of corrosion1. Clean, remove any corrosion and
2. Touch up with protective paint
3. Put a process in place to stop future damage
2ScalingMakes chemicals ineffective
Impact on the output of equipment
Loss of efficiency of the equipment
Potential reduction in flow rates
1. Clean with scale remover
2. Check water treatment process and make adjustments where needed
3BiofilmSimilar issues with Scaling
Impact on the output of equipment
Loss of efficiency of the equipment
Accelerate corrosion
Risk of Legionella growth
1. Clean with appropriate chemicals
2. Disinfect with appropriate chemicals
3. Check water treatment process and make adjustments where needed
4AlgaeGeneral fouling/staining
Provides a location for bacteria to grow
1. Clean with appropriate chemicals
2. Disinfect with appropriate chemicals
3. Review how algae are forming [light source] and try to remove
4. Check water treatment process and make adjustments where needed
5Dirt/Debris [leaves/other contaminants]Impact operation of equipment
Damage to equipment
Impact water flow
Impact filtration systems
Impact operation of fill pack
1. Clean and remove from the tower
2. Review frequency of cleaning
3. Inspect filters/screens to understand how entered the tower and if it can be avoided
6Silt/SedimentLocal corrosion where sediment collects
Impact on the efficiency of the equipment
Contamination of cooling water
Contamination of balance pipework
Impact on the chemical cleaning process
1. Check flow velocity as general build-up happens due to low flow areas in the tower
2. Clean with applicable equipment and chemicals
3. Review frequency of cleaning
4. Review water treatment process
5. Review filtration and, if effective
6. Review if the system would benefit from a sweeper system [link]
7Organic Deposits [oil/grease]Impact on the output of equipment
Loss of efficiency of the equipment
Accelerate corrosion
Impact on water quality
Impact on the water treatment system
1. Clean with appropriate chemicals
2. Inspect reason why deposits are happening and resolve to try to minimize future issues

Once the above has been completed, the physical cleaning of the cooling system, etc., can take place.

Step 8: Pre-Cleaning Disinfection

Using an oxidizing biocide [chlorine, bromine, chlorine dioxide] and a bio-dispersant, the cooling tower and water should be disinfected to ensure a safe environment and minimize risks for the engineers completing the works.

For the specific concentration, liaise with a chemical specialist for direction.

Once introduced to the system, the solution should be circulated throughout the system with the tower fans in the ‘off position.

This will allow mixing to take place through the system.

The time for the circulation should be agreed with the chemical specialist, below provides some guidance from the HSE Legionnaires disease technical guide [table “” not found /]

Minimum Circulation TimeMinimum Continuous Disinfectant Level [as free CI2]
5 hours5 mg/l
2 hours25mg/l
1 hour50 mg/l

Once the solution has mixed with the cooling water, re-energize the fans. This will ensure all of the disinfecting solution will interact and ‘touch’ all internal surfaces of the tower that will be wet during normal operations.

As the system runs and circulates the disinfecting solution, it should be sampled and monitored, adding more to the system if required.

The UK HSE document notes that ‘The normal disinfectant level required depends on the minimum circulation period adopted. A continuous minimum residual of 5mg/l as free chlorine, for a minimum period of 5 hours should be maintained.’

If there is a restriction on time, then a higher concentration can be used for a shorter time period. Still, before doing this, a review of system materials, etc., need to be conducted to ensure there will be no impact.

There is a correlation between the pH of the water and chlorine efficiency. Chlorine efficiency is reduced if the pH is over 8. To counter this, increasing chlorine is an option but not ideal. Other less risky measures would be to increase the bleed-off or adding other chemicals to reduce the pH and maintaining the chlorine mix.

If there are multiple towers on a system, then each should be sampled, etc.

Again, make sure to get advice from a chemical specialist on what would be acceptable for this work.

Step 9: De-Chlorination and Draining

Once the above has been completed, the next step will be to ‘de-chlorinate’ the system water to drain correctly.

De-chlorination is the process of removing the residual chlorine from the cooling water that was used to disinfect. This will allow it to be discharged safely into the local environment [ensure obtain any required permits etc.]

Sulfur Dioxide is usually used for this, but other methods can be carbon absorption, sodium metabisulfite, sodium bisulfite, and hydrogen peroxide.

Make sure to get advice from a chemical specialist as to what would be acceptable for this work and refer to any local needs/requirements to allow discharging of cooling water.

Once the de-chlorination has been completed, the cooling towers should be drained.

Step 10: Manual Cleaning of Cooling Tower and Components

At this point, the system will have been operationally understood, inspected, disinfected, and now be ready for manual cleaning of the tower and its components.

At this point, we need to understand the sequence of works that need to be completed. The below sequence of works could be used as a base. Notes on using high-pressure water jets: Using high-pressure water jetting to help clean parts of the tower and remove debris is usually quite common, but the risks should be understood, as the process will create aerosols and be considered during the method statement and risk assessment approval process. It is advised by the HSE that the following precautions should be taken and suggested included within the risk assessment.

  • Operatives should wear appropriate respiratory protective equipment, can refer to [HSE53 Respiratory protective equipment at work: A practical guide]
  • Consider people/members of the public nearby
  • Nearby buildings should be unoccupied, or
  • if nearby buildings are permanently occupied, windows should be closed, air inlets blanked off and ventilation systems shut down
  • Area being water jetted should be tented
  • Engineers and operatives completing the works are qualified, trained, and experienced

Equipment, Tools, and Documentation

All equipment tools and documentation should be available from the previous stages, which will allow the works to commence.

Readying the System for Cleaning

Make sure that the system is ready for cleaning, checking the following:

  • Chemical treatment/dosing isolated/switched off
  • Makeup water isolated
  • Condenser water supply isolated
  • Condenser water return isolated
  • Balance pipework isolated
  • Bleed off pipework isolated
  • Electrical supply isolated [locked out/tagged out]
  • Drainage, and if using filtration, is connected and hose discharging to appropriate drain
  • Water supply available and connected for providing clean water

Sequence of Cleaning

The following sequence can be used as a base for cleaning the tower, using the appropriate chemicals, equipment and assuming the basin is drained.

Ensure to log all cleaning and works, including photographs [before and after].

The sequence covers mainly an induced-type cooling tower.

Clean top of the tower

The best way to start is at the top of the tower, to allow the dirty water to drop into the cooling tower basin, where it will be cleaned at the end.

Clean all external surfaces and the inside areas that can be reached.

Tools/Equipment: Pressure washer, cloths, cleaning products, chemicals

Clean the hot water basin at top of the tower

The hot water basin feeds the tower fill pack and needs to be checked and cleaned to ensure no debris or scale buildup.

The filter should also be cleaned/changed.

Tools/Equipment: Cloths, cleaning products, new filter media

Clean the Drift Eliminators

The drift eliminators installed in the higher area of the tower should be removed, if possible, and cleaned to remove any buildup of foreign matter and scale. An acid clean can be used if there is scale build-up, using appropriate acid and inhibitor. 

Once clean, they can be reinstalled and checked to ensure the orientation is correct.

Tools/Equipment: Pressure washer, cloths, cleaning products, chemicals

Clean the Fill Pack/Mesh

The fill pack and mesh should be removed, if possible, and cleaned to remove any buildup of foreign matter and scale. An acid clean can be used if there is scale build-up, using appropriate acid and inhibitor. 

Once clean, they can be reinstalled and checked to ensure the orientation is correct.

If it is not possible to remove the pack, then it can be cleaned in situ by using the pressure w

If the pack does not clean effectively, then possible replacement may be required.

Tools/Equipment: Pressure washer, cloths, cleaning products, chemicals

Clean the Internals of the Tower

Once the fill pack has been completed, clean the inside of the tower, starting at high level and working down to the basin.

Tools/Equipment: Pressure washer, cloths, cleaning products, chemicals

Clean the Tower Basin

Finally, clean the basin of the tower removing all fouling, debris, and any silt build-up with the wet vac. Use the pressure washer to push debris etc., from the outside of the basin to the inside.

Be mindful if there is a sweeper system installed and not to damage it.

If using a sump pump to remove the dirty water, ensure that it drains to the sewer and put a sock on the discharge to catch any debris and silt, etc., so it does not clog the drain.

Tools/Equipment: Pressure washer, wet vac, cloths, cleaning products, chemicals

Spray system water through the tower

To help move any debris left behind from the cleaning process, allow the nozzles/hot water basin to operate, moving water down the fill pack and around the inside of the tower.

Check Tower Basin

Check the tower basin and remove any debris with wet vac that was flushed out from the previous step.

Tools/Equipment: Wet vac

Check and clean side stream filters

If there is a side stream filter installed, check and clean.

Step 11: Post-Cleaning Disinfection

Once the tower has been cleaned, the system should be refilled and then disinfected, as per Stage 8 above. Monitor the levels and top up if required.

Step 12: Putting back into Operation

If returning the cooling tower immediately back to normal operation, the disinfectant can be allowed to decay/reduce over the first few hours. An initial level of chemicals can be added, in line with advice from the chemical specialist.

If the system/cooling tower is not being immediately put back into service and expected to be left idle, the water should be dechlorinated, the tower drained, and flushed, leaving it empty.

When starting up after being idle, fill with fresh water, enable the water treatment programme, and include an initial startup dosage of chemicals.


Reporting and Recording of Data

As per the HSE requirements, all tower cleaning works should be recorded and available for future inspections. It is noted that the following items should be included within the report:

  • names and positions of people responsible, for carrying out the various tasks
  • a risk assessment and a written method statement detailing the tasks and control measures that are to be adopted
  • schematic diagrams of the water system
  • layouts of the water system
  • details of precautionary measures that have been applied/implemented and dates on which they were carried out;
  • remedial work required and carried out, and the date of completion
  • a log detailing visits by contractors, consultants, and other personnel
  • cleaning and disinfection procedures and including reports and certificates
  • results of the chemical analysis of the water
  • results of any biological monitoring
  • information on other hazards, eg treatment chemicals
  • cooling tower and evaporative condenser notification
  • training records of personnel
  • the name and position of the person or people who have responsibilities for implementing the written scheme, their respective responsibilities, and their 
    lines of communication
  • records showing the current state of operation of the water system, eg when the system or plant is in use and, if not in use, whether it is drained down;
  • either the signature of the person carrying out the work or other form of authentication where appropriate.

System Recommendations

Make recommendations on the system to the client or facilities team relating to control measures, inspection, and cleaning.


References

The following documents were referenced to provide some of the above information.

EPA Wastewater Technology Fact Sheet – Dechlorination

HSE Part1: The control of legionella bacteria in evaporative cooling systems


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