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Reducing the risks of solids deposition

Side-stream filtration reduces the risk of solids deposition and under-deposit corrosion in low-flow pipework, plate heat exchangers and radiators.

It can also be used to help maintain a low concentration of suspended solids in circulating water, following BSRIA-compliant pre-commission cleaning and flushing.

In addition, the longer-term benefits of the early installation of side-stream filtration means it maintains water quality throughout the ongoing operational functions of the system.

Generally, to achieve BSRIA BG29/2012 criteria, side-stream filters should remove particles as small as 5/1,000th of a millimetre (5 micron) and must turn over the system volume within a 24-hour period.

It is critically important to have the right chemical inhibitor circulating through the system. One of the characteristics of a good chemical inhibitor is that it should break down any sludge to release and lift debris into the system flow before it finds its way back to the side-stream filter for capture.

There are a number of types of side-stream filters on the market. Some support the use of media beds, some are anti-cyclones and others have filter bags or cartridges.

However, all have a built-in circulating pump to run the filter and most have BMS interface to inform building owners when filters are blocked.

A number of side-stream filters use back flushing and disposal of the waste direct to drain. This means that if the waste is automatically removed and disposed of, the maintenance team is un-able to see whether or not the system is corroding. The evidence simply disappears without any visual checks.

Therefore, for optimal performance a good side-stream filter should be married to a good inhibitor. It should also be capable of being checked every time a filter is changed.

Ask yourself: why has the filter got blocked? If it is on an old system, the amount of time between filter changes should be increasing; if it is a new system, you need to investigate further.

In an age when we need to curb energy use for building owners, can we not simply use the system circulating pumps to run the side-stream filter?

For instance, if the heating system and the system circulating pumps are off during the summer period, the side-stream filter does not need to operate as it would just be a waste of energy.

Similar to a traditional dosing pot that uses the differential pressure of system pumps to dose chemicals into the system, the side-stream filter can use the system pumps to clean up the system.

Better still, what about a dosing pot that becomes a side-stream filter and costs next to nothing to run? So what is the most effective type of side-stream filter? You decide.

Richard Harrison-Cowley is director of research and development at Vexo International

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