Modern Building Services

MODERN BUILDING SERVICES MARCH 2023 29 FEATURE PIPED SERVICES, PUMPS ANDWATER What are the key indicators of corrosion? The introduction of real-time monitoring technology for closed circuit systems has really changed the game in terms of corrosion control. Previous to this, sampling and corrosion coupons were the only monitoring options; and while both still play a role in HVACmanagement, we now have the technology to pick up the early warning signs and intervene at amuch earlier stage before corrosion has occurred. Corrosionmonitoring systems detect awide range of parameters in real-time, with live readings taken every 15minutes and sent direct to responsible parties.Whenwe studied this, over 1,800 alarmswere triggered over an 8-year period; detecting a range of problems that would largely have remained invisible under the old system. Frommost to least common, the causeswere: High dissolved oxygen – 25% of alarms Closed heating / chilled water systems need to be air-tight to prevent the ingress of dissolved oxygen. For a typical closed system, dissolved oxygen levels should be around 0.1 to 0.2mg/L. Oxygen is the precursor of most types of corrosion. Pressure – 22% of alarms Positive (but not excessive) pressures must be maintained to prevent air being drawn in. Conductivity/dosing – 22% of alarms For systems dosed with chemicals, conductivity is directly related to concentration. Measuring this parameter is essential to ensure that minimum thresholds aremaintained, otherwise inhibitors are ineffective, and glycols offer insufficient freeze protection. Conversely, over-dosing is environmentally unacceptable and an expensive waste. Temperature – 15% of alarms This is a key parameter of any HVAC system and needs to be constantly checked to ensure it is operating at the intended level. pH – 7% of alarms Must be maintained within the limits set by the chemical supplier in order to ensure metals are immune from corrosion or adequately passivated. Crevice corrosion – 7% of alarms Crevice corrosion can occur even if general corrosion rates are low. It occurs in localised regions, such as weld seams, crimpled joints or under debris, due to differential aeration effects and is a frequent cause of pitting attack and pin-holing. Galvanic currents – 2% of alarms The galvanic current is the current that flows between different metals within a system, for example, steel and copper. Maintaining low galvanic currents is indicative of low oxygen levels and/or good inhibition of metallic surfaces. Make the connection By monitoring all these parameters together in real-time, responsible parties are able to identify the root cause of a problem, enabling early intervention and preventing costly downtime and repairs. For instance, oxygen ingress can be caused by pressurisation issues or the demand for fresh make-up water as a result of a leak or planned drain-down. The latter would also explain why conductivity (related to dosing level) was decreasing, indicating a need for remediation and chemical top-up. How much does prevention save? As buildings become smarter and more connected, the stakes become much higher and the manual monitoring approach is simply no longer fit for purpose. With real-time monitoring systems installed, either built-in from the start or used for short or long-term maintenance outcomes, savings can be made across the board. If a water system fails, costs will not only be incurred through replacement and refit, but also management and consultancy, and any legal bills. For a large system there are some examples where these costs have exceeded £10m in replacement and legal fees. Even the cost of remediation (investigation, replacement of parts and recommissioning/water treatment) will exceed £100k in most circumstances. A closed water system that doesn’t break down, doesn’t suffer from corrosion, and runs at peak efficiency, is saving huge amounts of money long-term and it is only through 24/7 real-time monitoring that this operational certainty can be achieved. Behind the scenes and hidden from view, corrosion is a huge problem for some of the UK’s most critical infrastructure. With effective real-time monitoring technology in place, it is possible for responsible parties and facilities managers to identify the precursors of corrosion and make early interventions to prolong the life of valuable HVAC assets – potentially savings millions of pounds in the process. We have published a white paper, ‘Behind the scenes of closed-system HVAC’ 1 which examines its findings over the past eight years and introduces the new range of corrosion monitoring technology. Source 1 www.hevasure.com/news-insight/ closed-loop-hvac-systems-explained- faqs More information can be found at www.hevasure.com