Industry best practice may not be enough to prevent costly corrosion in HVAC systems, argues Steven Booth, Associate Director at Guardian Water Treatment
Corrosion is a serious issue when it comes to HVAC systems, causing breakdown and inefficiencies and adversely affecting water quality. How a water system is specified, designed and constructed has a big impact on the future likelihood of developing corrosion, and it’s a good idea for the FM to be involved at the planning stage if possible. Correct construction and pre-commission cleaning are the vital first steps – a ‘fit and forget’ mentality will cost more in the long term.
Pipe material is an important factor. Low temperature hot water (LTHW) and chilled water systems are sometimes made from stainless steel as it is corrosion resistant. However, the components that fit the system together are usually made from copper, brass or mild steel, which are not corrosion resistant and are therefore a potential focus of degradation. Regardless of pipe material, it’s important to continually monitor the conditions that cause corrosion (especially dissolved oxygen). This opens up more options. So long as dissolved oxygen is minimised, for example, lightweight and lower-cost carbon steel is a perfectly good choice.
Bacteria can also be a contributing factor in causing corrosion, so a water system should be designed to avoid areas where water can stagnate. Dead legs, which are often included to allow for ‘future connections’, are an example. Plans should be checked for any potentially problematic areas further down the line.
Pre-commission cleaning is vital to ensure that when a water system is handed over to the FM team, it starts life in the best possible shape, with debris and bacteria flushed away. There’s a risk that over-flushing of water and chemicals at this stage could cause pitting in the pipework, potentially shortening its usable life, so flushing should be kept to a minimum to reduce system aeration.
The innovative Hydrosphere solution reduces the volume of water used during pre-commission cleaning without compromising the effectiveness of the process. Given that half the water used in constructing a building is generally consumed during pre-commission cleaning, this is good news for sustainability.
Remote and continuous monitoring of system parameters should also begin at this stage, to ensure any potential issues are flagged up early. BSRIA best practice guidelines focus on sampling and laboratory analysis, but this is open to interpretation and may prove to be too little, too late. Round the clock, real-time monitoring of important system parameters such as dissolved oxygen, pressure, conductivity and corrosion rates will provide a more accurate picture.
The integration of zones within a system can cause a lot of problems. This can occur at the fit-out stage, or when changes take place further down the line. FMs need to protect their main systems and ensure that fit-out or refurb projects follow the protocols as advised in BG29. Even if these guidelines are followed to the letter, however, issues with water loss and oxygen ingress can cause disruption to base build water quality, leaving the FM to pick up the bill.
Monitoring is key during these periods of disruption, to identify issues with the system before the FM is left to deal with them. Too often the fit-out programme takes precedence over the quality of the water system left behind. According to BG50, frequent monitoring is desirable for the first six months of operation of any new system, and immediately after any significant system changes, such as the replacement or addition of plant or terminal units.
Following handover, monitoring should not stop. The key identifiers of corrosive conditions are oxygen and microbial growth, which can lead to microbial influenced corrosion (MIC). Using the Hevasure system, a range of parameters can be checked, including pressure, corrosion, inhibitor and pH levels. Not only will this identify corrosive conditions and potential leaks before they become big issues, it puts the power back into the hands of FMs. Consultants become largely redundant when you can see for yourself the condition of your water system.
By having a full understanding of system conditions, problems can be dealt with rather than covered up (which may also lead to savings). Overuse of inhibitors is a common reaction to dealing with high oxygen levels. A better approach is to find the root cause and solve it – chemicals should be considered as a secondary line of defence, not a solution.
When maintenance does take place, care must be taken to minimise the amount of oxygen re-entering the system. Pressure settings must be kept at the correct levels – if they exceed pressure relief valve (PRV) settings, this can lead to water loss, which means more aerated water will need to be added. Under-pressurisation will cause air to be sucked in through air vents and dissolved oxygen rising to dangerous levels.
Recent high-profile cases of corrosion have resulted in a total bill for system replacement, collateral damage, investigation and legal charges exceeding £1 million. Taking steps to prevent corrosion from the outset, and ensuring monitoring is integral to water systems management, will save money in the long term, and may also result in more cost-effective and sustainable working practices.
The downside of ducted HVAC systems is that they provide potential conduits for heat and smoke to spread should a fire break out in a building. By its very nature, ducting presents an open channel for air movement. That’s why dampers exist and why they’re required by building standards to ensure that, if a fire does start, they shut either through the action of the blaze itself (fusible link) or via actuation linked to a fire alarm or smoke detection system.
Unfortunately, while dampers generally operate properly when they’re first commissioned, records of their installation can be lost over time. This means that a few years down the line building owners and FMs are left without a clear idea of how many dampers are in their building or where, exactly they can be found – especially if the building has undergone any structural alterations or changes of use, or if FM responsibility has changed hands. It doesn’t help that dampers are generally not on display and are frequently difficult to physically access.
Dampers, like any piece of life safety equipment, need care and attention to make sure they’re able to function in the way that’s expected of them. RRO recommends hefty fines and custodial sentences for not taking fire safety maintenance seriously enough – but how are FMs supposed to stay on top of damper maintenance if they don’t know where they are, how many there are, or what state of repair they may be in? The only way to remedy the situation is by carrying out a costly survey.
This is why proper management of damper data makes all the difference. Having an organised system of maintenance logs and scheduled reviews means HVAC systems remain safe, reducing the need for surveys or avoiding them altogether.
It might seem easier in the short term to pay a maintenance contractor to check your dampers, but there are long-term benefits from using a specialist who understands the unique challenges of fire safety service and can properly log the status of your dampers (with photographs). This will assist compliance and yield significant long-term savings.
Bob Gate is UK Business Development and Marketing Manager at Brakel Airvent.