Efficiency, longevity, and safe operation of closed-circuit process chillers are critical and should be top of mind for those who are responsible for them. Chillers are the backbone of commercial and industrial cooling systems.
However, they are not a ‘fit and forget’ solution, and there are some easy ways to look after your chiller to ensure it lasts 10 years and more.
Water treatment is a fundamental part of a chiller’s operation and maintenance ensuring efficient and reliable operation.
Most maintenance engineers know that if a chiller’s water and glycol mix is incorrect, the effects can be rapid and disastrous, leading to corrosion, system deterioration, and leaks, as well as the build-up of rust, scale, biofouling and other debris.
All this can reduce the efficiency of the chiller and damage its components, ultimately leading to costly running, repairs or replacement.
Having no water treatment plan can cause issues to even new chillers. The chiller in this image is only 18 months old.
Essential water treatment checks for chillers
1. Don’t forget inhibitors
Glycol is an essential element of any heat transfer fluid used as part of a chilled water system, as it allows the fluid to be sufficiently chilled without freezing. However, an uninhibited glycol system can pose even more of a risk than plain water due to the highly corrosive nature of most glycols.
This requires inhibitors to be used at all times. Corrosion inhibitors are multifunctional hence careful selection is key. Their presence can include interference with the natural corrosion cell process, the buffering pH, and the formation of a protective film on the surfaces of the chiller’s components. Scale inhibitors prevent the precipitation of dissolved minerals, thus reducing the formation of scale build-up.
For those operating in areas where there is a risk of incidental human contact, such as the food or the pharmaceutical processing industry, the wrong inhibitors in an MPG solution, which is purpose designed for such applications, creates a serious contamination risk, but an NSF-accredited glycol overcomes that concern.
2. Monitor build-up of biofilm
The build-up of biofilm within the closed-circuit systems is one of the few key problems encountered during the maintenance. The build-up of biofilm and other detritus will not only affect water flow, but also prevent (film forming) corrosion inhibitors from working effectively with possibly catastrophic results.
The key to the effectiveness of a corrosion inhibitor within a closed-circuit system is ensuring complete contact of the inhibitor with the metal surfaces.
Cleaning out any “dirt & debris” from pipework can be difficult, however, it is made much easier using online cleaning products available on the market.
Cleaning out any “dirt & debris” from the pipework delivers both financially and environmental benefits including:
– Saving on energy costs due to increased heat exchange efficiency from both the process and plant
– Extended capital plant life expectancy for plants, pumps, heat exchangers and pipework
– Reduced downtime, avoiding loss of critical plant or equipment
– Saving on expenditures related with any unforeseen costly and untimely maintenance and repairs
– Improving Health & Safety by reducing microbiological contamination and running a cleaner system
3. Take regular water samples from various parts of the system.
Corrosion and degradation can happen anywhere within a system and it’s not enough to take water samples from just one location. Samples need to be taken from strategically positioned access points around the system and especially from high-risk areas such as heat exchangers, cooling jackets and any other sensitive product-fluid interfaces.
4. Test and monitor fluid pH levels
Not taking pH level readings as part of routine water sampling can have a major negative impact on the system’s performance.
As pH drops, acidity increases, and the corrosion rate increases as well. The reason for this is that low pH solutions (as we move further away from neutral pH 7) accelerate corrosion by providing hydrogen ions. Hydrogen attacks and damages the surface of steel and increases the corrosive effect.
Two metals commonly seen within heat transfer loops are copper and aluminium due to their conductive performance. However, these two metals are particularly sensitive to pH reduction. Copper is resistant to corrosion in the presence of oxygen in water because copper forms a stable layer of copper oxide on its surface, thus reducing the oxygen effect we see in other construction materials. Below pH 6.5 however this ‘protective’ copper oxide layer breaks down and with it the creation of a galvanic corrosion cell.
While chiller pH tolerances vary slightly depending on the materials used, I would recommend limits of 8.0 – 8.5. Incorrect pH levels may indicate that either not enough inhibitors have been used, or the glycol levels are too concentrated.
Both scenarios can very quickly cause high levels of corrosion throughout a system if left unchecked, leading to costly maintenance bills and unplanned downtime. Water treatment chemicals can ‘adjust’ the pH level using their in-built buffering chemistry and maintain it within the optimal range.
5. Check the clarity of the sample
Not all tests are as in-depth as pH level, and one of the most obvious signs that a chiller system is degrading or corroding internally is when there’s visible debris in the water sample. A water sample from a chiller operating correctly should be clear and if it’s not, then there’s already some internal system damage. This needs to be addressed immediately as the debris can soon lead to blockages in key areas of operation such as the heat exchanger, which will rapidly decrease the chiller’s efficiency.
6. Chemically flush your system and chiller immediately after installation
As soon as a new chiller is installed, the whole system should be flushed immediately to ensure the fluid is completely free from contaminants and at the highest quality possible, with no legacy debris or surface contamination present to cause damage to the fluid, the pipework and the new equipment. This golden rule should be followed whether it’s a permanent or temporary installation for planned or reactive maintenance.
7. Watch out for bacteria
The correct water treatment chemistry helps to prevent the growth of microorganisms in the chiller’s water system. Microorganisms such as bacteria and bio-filming organisms can thrive in some of the harshest of environments and when allowed to proliferate can cause a variety of problems in process chillers.
As we understand the ubiquitous nature of bacteria, we need to make assumptions that there is every likelihood that a number of bacteria are going to be introduced into our water systems including closed system circuits.
The most common process bacteria undertake is the production of biofilm. Such biofilms can harbour and allow to grow a multitude of numerous individual micro-organisms as well as capture system debris. With a build-up of biofilm which can be rapid (given all the right conditions) we can expect a number of costly issues to occur including reduction in efficiency, flow restrictions and pipework failure.
Evaluating the status of both protective chemistry and microbiological presence is fundamental to help ensure we have clean, efficient and protected systems, anything other is going to be costly. Therefore we need to proactively test and, where required, undertake appropriate corrective treatment like using biocides.
In conclusion, water treatment is an essential part of maintaining process chillers and can extend the life of the chiller’s components, improve its efficiency, and reduce its operating costs. It’s essential that your system fluid is checked, maintained and treated regularly to avoid problems ultimately leading to equipment and process system failure, inconvenience and expense.
Given the intricacies of taking a thorough and correct chilled water system sample, sometimes it pays to call in an expert. Regular water sampling and off-site laboratory analysis is available as part of some chiller manufacturer’s aftersales and servicing packages – including Planned Preventative Maintenance Packages (PPM) from ICS Cool Energy.
By: Dave Palmer, General Manager for the UK at ICS Cool Energy