SPONSOR CPD PROGRAMME Continuing professional development (CPD) is the regular maintenance, improvement and broadening of your knowledge and skills, to maintain professional competence. It is a requirement of CIBSE and other professional bodies. This Journal CPD programme can be used to meet your CPD requirements. Study the module and answer the questions on the final page. Each successfully completed module is equivalent to 1.5 hours of CPD. Modules are also available at www.cibsejournal.com/cpd Chemical-free water treatment This module considers chemical-free water treatment in closed-loop water systems in building applications such as heating and cooling This article outlines the factors that drive the need for water treatment in closedloop water systems and focuses on the processes that provide chemical-free water treatments. It also explores how such systems provide treatment of closed-loop water systems, such as those used in heating and cooling systems for buildings. Water treatment is typically undertaken at the pre-commissioning stage and as an ongoing process to establish and maintain water quality. This ensures that the circulating water does not become contaminated with particulate matter, bacteria or other harmful substances (such as shown in Figure 1), which can lead to system failure. As discussed in the comprehensive guide BSRIA BG 50,1 appropriate water treatment can help to inhibit corrosion and protect the metal components of the system, so reducing the opportunity for leaks, reductions in efficiency and, ultimately, system failure. It can prevent the formation of scale on the inside of pipes, fittings and heat exchangers that will otherwise reduce the efficiency of the system and reduce system reliability. Appropriate water treatment can also control microbial growth, helping to prevent bacteria and other microorganisms that can grow in closed systems, causing problems such as corrosion and fouling. Monitoring and controlling the water quality across the life of the installation will improve system performance, lower energy costs, reduce the need for repairs and maintenance, and potentially extend the life of the system. There are several parameters that will impact the water quality in closed-loop systems. Oxygen dissolved in the water acts as a powerful oxidising agent, readily interacting with metals and accelerating corrosion processes. Dissolved oxygen may be minimised through proper system design, degasification, and by maintaining a closed loop with minimal air ingress. Total dissolved solids (TDS) an amalgam of minerals, ions, and other dissolved substances in the water will increase the waters electrical conductivity and impact the rate of scale accumulation and corrosion. Water hardness is specifically identified as the amount of calcium and magnesium salts in water, generally in the form of bicarbonates, chlorides and sulphates that, if left, will accumulate as insoluble carbonate (scale) in water systems. Chloride ions are notorious for promoting localised corrosion, as they can penetrate and destabilise the naturally forming protective oxide layer, leaving the underlying metal vulnerable to corrosion. The acidity or alkalinity of the water, as measured by the pH, significantly influences corrosion rates. Generally, lower pH (more acidic) environments increase corrosion, as this dissolves the protective oxide layer on the surface of metals, leaving the underlying metal exposed and vulnerable to corrosion. Conversely, slightly alkaline environments can help thicken the protective oxide layer, offering better protection although excessively high pH can induce other degradation processes (such as disrupting the passivity of stainless-steel components). Higher pH will tend to reduce most bacterial growth. However, the bacteriological quality of the water will be highly dependent on the cleanliness of the initial system and the fill water. These factors interact and influence each other, so a holistic approach considering www.cibsejournal.com March 2024 49 CIBSE March 24 pp49-52 CPD Module 230.indd 49 23/02/2024 13:55