This technical troubleshooting guide looks at closed water systems, highlighting the most common problems that affect such closed heating and chilled water systems. The guide examines the problems of scale, corrosion, foaming and the build-up of bacteria and biofilm in closed loops. It also gives guidance on the selection and application of specialist water treatment chemicals designed to tackle specific issues.
Troubleshooting closed water systems
Many of the problems that affect closed heating and chilled water systems, such as scale and corrosion, can also affect open water systems.
However, one of the main differences in a closed water system is that the water is encapsulated in a closed loop arrangement and so can be chemically treated at much higher and consistent concentrations, given that there is none of the water (and associated chemical) loss typically associated with open systems.
There are a number of problems which crop-up frequently when considering both the on-going maintenance and water testing of closed loop systems… and each problem has a different chemical treatment solution which works best at dealing with it.
Dealing with scale formation in closed systems
Closed systems generally don’t suffer from serious scaling issues, unless the water used to charge the system initially is particularly hard.
Scaling can also occur if make-up water added to the system periodically to top-up water levels is particularly hard.
If however, you are experiencing high levels of calcium carbonate (scale) inside the water system, then you should consider using an on-line descaling product which can be dosed in to the water.
This type of on-line de-scaler will gradually decrease the levels of scale as the system runs as normal.
Dealing with calcium carbonate deposits which have built up on the internal pipework surfaces can also help to prevent under deposit corrosion.
Descalers can also save you money on your energy bills by restoring heat transfer efficiencies – as scale can act as an unwanted insulator.
How to control high copper levels in closed water systems
If you have detected high levels of copper in your closed loop water system, then one of the best treatment methods is to add in an azole based film-forming inhibitor.
Such products work by forming a protective barrier on the surface of the copper which helps to protect it.
Ideally you should look for a copper corrosion inhibitor that contains enough azole to also protect small amounts of yellow metal within the closed system from becoming corroded.
If your pipework system is extensive with lots of copper present, then you might need to add a separate yellow metal corrosion inhibitor to make sure that you have adequate levels of protection against both copper and yellow metal corrosion.
Controlling foaming in closed-loop systems
Foaming can affect closed systems but is less common than problems such as corrosion and scaling… if it occurs however, it still needs to be dealt with effectively.
Foam found in a closed water system is usually due to poor system design, and a high rate of water flow through the pipework.
Adding a low dosage of a special antifoaming agent can help resolve these issues.
Nitrite reducing bacteria (NRB) and reduced nitrite levels
If you are already dosing your closed water system with a multi-metal corrosion inhibitor, and you have determined through water testing that you have appropriate levels of molybdate, but are still struggling with nitrite levels that are significantly less than 250 parts per million, then the most likely culprit is nitrite reducing bacteria, or NRB.
If your system has been colonised by this type of bacteria, then you need to consider adding an appropriate biocide into the water system to deal with it.
Once added allow the biocide to circulate around the system for around one week, and then test again to ensure that you have managed to get bacterial levels under control.
When you are confident that the nitrite reducing bacteria are under control you should then look to add a nitrite supplement to bring the levels in the water back up to greater than 250 parts per million.
Controlling biofilm in closed loop systems
Even when biocides are being added into your system, sometimes this isn’t enough to bring the levels of bacteria and microbes down to acceptable levels.
The most common reason for this stubborn build-up of bacteria is due to the formation of biofilm (or slime) in the system.
This slimy biofilm forms a protective barrier or shield that sticks to the inside surfaces of the system, protecting the bacteria and preventing the biocide from doing its job
Over time, the bacteria break free from the biofilm to re-contaminate the water in the system.
The build-up of biofilm can be treated by dosing a special chemicals called bio-dispersants, designed to disrupt the biofilm, lifting the film away from the surface of the pipework so it can then be removed.
An added benefit of using bio-dispersant chemicals in a closed water system is that removing the biofilm from the pipes will also prevent corrosion forming under the slimy deposits, and ensure that any corrosion inhibitors used are fully in contact with the surface metals to protect them.
Bio-dispersants are typically used in conjunction with a biocide to control the overall numbers of bacteria.
It’s important to remember that once it’s been dislodged, the biofilm has to go somewhere in the system.
Consider also the possibility of clumps of free-floating biofilm blocking smaller pipes entirely.
If your pipes are wider, then strainers added into the system will collect any larger clumps of slime that are dislodged.
Once the bio-dispersant chemicals have been added, any strainers fitted to the system will need to be removed and carefully cleaned regularly to ensure the closed system doesn’t block.
Selecting water treatment for closed loop systems
You should always seek specialist advice when developing a water treatment programme for closed heating and chilled water systems to ensure any chemical additives used are the most appropriate for your needs, given the individual specification and design.
Closed water system experts
Water Treatment Services offer a comprehensive range of solutions for the management of closed heating, chilled and cooling water systems.
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