Closed system water treatment: Ensuring heating and chilled water systems are adequately treated

Although the management and maintenance of the closed systems (also known as ‘closed circuits’ or ‘closed loop’) within buildings are of paramount importance, they are sometimes overlooked. In a closed system, water does not – in theory – come in to contact with air, and so reduces the chance of contamination.  However, as closed systems are very rarely truly closed, they are not maintenance-free.

The boilers, chillers and associated plant and pipework which heat and cool buildings are likely to contain dirt, debris, mill scale, particulate matter and, potentially, biofilm. All of these can be introduced during the installation process and, if left in the system, can drastically affect the performance of the systems and lead to general decline and increased wear. This can occur through the build-up of scale, corrosion of pipework and metallic surfaces, especially heat exchangers and wear on seals, pump impellers and all surfaces, especially where there are bends in pipework.

Unwanted particulate matter travelling round the system and impacting surfaces causes general wear – in essence like ‘liquid sandpaper’ continually eroding the fabric of the systems. This can eventually lead to blockages and loss of performance through reduced flow rates and leaks. These often occur in the most inconvenient places, such as above false ceilings where fan coil units are installed, at joints of radiators, etc., where leaks will often spill onto tenants’ carpets. Additionally, these issues will reduce the life span of some of the most expensive equipment within a building – the boilers and chillers.

Pre-commissioning closed systems

The aim is to avoid or minimise the issues outlined above as far as is ‘practically possible’. Scale and corrosion will always occur within heating and chilled water systems to some degree. Similarly, because of the nature of flowing water, there will always be some erosion and – due to the tenacious ability of microorganisms to colonise even the most inhospitable of environments – it is rare to find a system that is free from any microbiological contamination. To that end, when a building is being fitted out and systems are being tested and commissioned, there are procedures to follow regarding chemically cleaning and flushing the closed water systems during the various stages of installation and commissioning, as outlined in BG 29/2012 Pre-Commission Cleaning of Pipework Systems. Following that, the systems are to be dosed, where relevant, with scale and corrosion inhibitors to minimise scale formation and slow the corrosion process to acceptable levels (corrosion can never be stopped entirely, as any metal will want to revert back to its original state as a metal ore), biocides to control microbiological growth and Glycol to prevent freezing.

Routine testing of treatment levels within closed water systems

Unfortunately, even when the above tasks are carried out thoroughly, as outlined in BG 29/2012, there is often a lack of documentation to prove this, especially in older buildings, where there have been a number of changes of ownership over the years. Additional complications include:

1. Closed systems are very rarely truly closed and there will always be some losses to a degree, which will reduce the effective concentrations of inhibitors and biocides dosed and, additionally, there can be ingress of oxygen (which will accelerate the corrosion process), and potentially biological growths or debris which are often present in feed and expansion tanks
2. Tenants will carry out additions and alterations to the closed water systems during their fit-outs. When they connect into the main heating and chilled water systems, they can introduce contaminants or simply dilute the treatment chemicals already within the system if they don’t follow the principles outlined within BG 29/2012 and, additionally, BG 50/2013 Water Treatment for Closed Heating and Cooling Systems.

How the S₂ Partnership can help

A comprehensive, thorough audit of the closed water systems within a building will provide the confidence that the systems are adequately dosed and treated to minimise the deleterious effects that excessive scale, corrosion or bacteriological growth can have on not only the efficiency of closed water systems but, ultimately, the longevity. An audit will also help minimise the adherent problems that reduced flow rates, blockages or leaks will undoubtedly cause if closed water systems are not appropriately maintained. Contact us for further information.

Our team of dedicated and professionally trained staff ensure the ability to deliver a comprehensive and effective water management service. The S₂ Partnership is a member of the Legionella Control Association, delivering key services including risk assessments, consultancy, training and analytical services.

The S₂ Partnership Registration Certificate can be viewed here. To see a current copy of the Legionella Control Association Code of Conduct which S₂ Partnership comply with click here.