5 Products that perform | Service that delivers | People that care From a system point of view, good design and operating conditions with a well-planned pipe layout and flow velocities build the first step to corrosion control. Additionally, regular maintenance and monitoring are advisable. If corrosion is a concern due to the results of the water analysis such as high conductivity and chloride levels, there is a range of chemicals containing orthophosphate, polyphosphate and sodium silicate (with/without added zinc) available which are safe for use in drinking water systems. Other options such as anodes to protect water heaters and hot water storage tanks from corrosion also exist, visit hamworthy-heating.com/ water-heater-corrosion-protection for more information. When it comes to system design, the potential difference between metals in a heating system is important to consider. When more noble and less noble metals are used in the same system, corrosion can occur. The bigger the potential difference between them, the bigger the risk. @hamworthy @heatingatwork hamworthy-heating-ltd HamworthyHeating Corrosion – Chemical or physical protection? Hard water contains a high amount of calcium carbonate and often magnesium bicarbonates. When water gets heated up, scale forms and deposits on equipment, which can lead - in the worst of cases - to its breakdown. In the ‘best’ of cases, it affects the performance, making it run less efficiently which increases running costs. Scale is the most common problem in hot water systems, given large parts of the UK are hard water areas. The graph on the right shows how scale thickness affects the efficiency of a water heater. The materials used in a hot water system play an important part in whether biofouling occurs or not. While microorganisms are always present in the form of a biofilm, they can gather more easily on rougher surfaces. However, even smooth surfaces aren’t entirely 'immune' but lower the risk. Biofouling eventually develops where the problem gets out of hand. As the microorganisms feed on organic and inorganic substances contained in the water and can multiply rapidly, it is important to keep them at bay. When corrosion is present, dangerous pathogens in the biofilm have an even better chance to thrive. 1 One of these are Legionella bacteria. For this reason, the system design should avoid dead legs where they can grow under favourable temperatures (20-45°C). Following HSG274, a guidance for duty holders such as employers, landlords, and others in charge of buildings e.g. facility managers, hot water should be stored at 60°C or higher and distributed at 50°C or higher (55°C in healthcare premises). 2 In water heaters, a built-in legionella protection cycle which automatically heats up the water to this temperature at certain intervals can provide safety. To avoid scalding incidents, thermostatic mixer valves (TMVs) need to be fitted. 3 These are already mandatory for new build domestic bathrooms. 4 Guidance for buildings that are used by the public such as healthcare premises, care homes, schools, hotels and leisure facilities, also recommends the installation of TMVs. No economies with scale Biofouling and Legionella Finishing off the installation (disinfection) It is recommended to carry out a disinfection according to HSG274, once the hot water system has been installed, followed by a system flush until all chemicals are removed. To protect the aquatic environment, a so-called consent to discharge might be required when the system is drained. To test if the disinfection was successful, a bacteriological sample should be taken a week after it has been performed. Prepared for the future After the disinfection and when the system is ready to take up operation, Hamworthy recommends consulting a water quality professional to commission the water quality of the system. Commissioning sheets and water quality certificates are then kept for future reference. Anodes also require regular check-ups as they need replacing when worn down to 60 per cent to ensure continuing protection. If any water treatment equipment is installed, this also needs to be regularly looked at. Other than visual checks, regular water samples should be taken to monitor water quality, also on a bacteriological level. Designing a safe and efficient hot water system depends on many factors. Therefore, a bespoke approach to design, equipment and material choice is necessary for each individual application. Lastly, it is a matter to find a balance to overcome all the risks. Find out more If you would like to know more about water treatment of domestic hot water systems, take a look at ICOM’s Water Quality Consideration of Domestic Hot Water Systems for Commercial Applications Guide which has been developed in cooperation with ICOM members to promote best practice in hot water systems: www.icom.org.uk/users/register/ 1. https://www.researchgate.net/publication/11162443_ Biofouling_in_water_systems_-_Cases_causes_and_ countermeasures 2. http://www.hse.gov.uk/pubns/priced/hsg274part2.pdf 3. http://www.hse.gov.uk/healthservices/legionella.htm 4. https://assets.publishing.service.gov.uk/government/ uploads/system/uploads/attachment_data/file/504207/BR_ PDF_AD_G_2015_with_2016_amendments.pdf Interestingly, compared to most other compounds, calcium carbonate becomes less soluble the higher the water temperature, increasing the presence of scale-forming salts. This is the reason why problems occur especially in hot water applications. However, high temperatures are needed to prevent the growth of Legionella bacteria. Regular maintenance is vital to ensure an efficient and reliable system. This means the installation needs to be cleaned and scale removed. If hard water becomes an issue, a physical water softener or chemical treatment can be an option.