The following briefly explains why Closed Systems require cleaning, and the two main methods of carrying out a sufficient Chemical Clean.
All natural water carries an amount of suspended solids, mainly carbonate deposits, Lime-scale and many other minerals, which over a period of time, especially in systems which have not been adequately treated with an appropriate Water Treatment programme, the system water will also pick up other deposits, such as corrosion.
As with any material, water can only hold a certain amount of solids / deposits in suspension, and at some point, these deposits will drop out of suspension as “Slugde”.
This sludge will build-up mainly at the low flow area’s of the system, such as Fan-Coil Units, radiators and Heating / Chilled Water Coils within Air Handling Units.
As the sludge builds up, this gives bacteria, most commonly Pseudomonas and Nitrite or Sulphite Reducing Bacteria, a perfect habitat in which to proliferate at high rates.
Once a system has a bacterial contamination confirmed, it is imperative to react quickly, as not only does the sludge / debris deposits reduce the efficiency of the system dramatically, the bacteria will notably lead to “Metabolic Corrosion”, which is a high rate of corrosion in a small area which causes system leaks, and the bacteria is also known to attack pump seals and valve glands.
There are two main methods of carrying out Closed System Cleaning for either Chemically Cleaning a system to remove the corrosion and sludge / debris deposits, or carrying out a Biocidal Clean to neutralise and remove a bacterial contamination:
Chemical Clean, Dynamic Flush and Retreat:
This is the process of carrying out an initial Dynamic Flush, or sometimes referred to as a “Balance Flush” to remove the majority of the suspended solids prior to adding an appropriate chemical cleaning agent to either neutralise any bacterial contamination present or remove iron-oxide from the internal surfaces of the system, and help lift any debris into suspension.
Once the Chemical Clean / Biocidal Clean has been completed, the system is then Dynamically Flushed to remove all suspended deposits to within at least 10% of the Incoming Mains Water quality. Once achieved, the system is then treated with an appropriate corrosion inhibitor to stop further corrosion taking place.
This process can be carried out with the system on-line with existing systems, or the system can be “Pre-Commission Cleaned” on new systems prior to going on-line.
This process requires a Side-Stream Filtration Unit to be installed on the system to be cleaned.
Once installed, this unit will pass a proportion of the system water through a media filter to remove the suspended solids. Initially, a low grade media filter would be installed to remove the larger particles, thus not blocking the filter with the fine particles which block the media, therefore not allowing the system water to circulate through the unit.
Over time the filter media is gradually replaced with finer media filters, until the system water has no suspended solids remaining, and is defined as “Polished Water”.
There are mixed opinions as to whether the system should be chemically cleaned prior to installing the Side-Stream filter, or if the chemicals can be added after the installation.
If the cleaning agent is added after the installation, the cleaning process will greatly increase the amount of suspended solids to be removed, therefore taking longer to clean the system, greatly increase the amount of media filters to be used, and increases the amount of labour required.
If the system is to be cleaned prior to the installation, is there a need for Side-Stream filtration if the initial system clean has been carried out to a high standard?
There is also a matter of opinion as to when the system is to be treated with the corrosion inhibitors. If left until the system is Polished, there will be the risk of “Flash” corrosion within the system whilst the system is un-treated, thus the cycle continues, and if treated initially, the suspended matter, any active corrosion and water losses whilst replacing the filters will deplete the active reserve of the inhibitors.