Energy efficiency
www.heatingandventilating.net Well maintained HVAC
systems can improve energy efficiency significantly
Corrosive concerns I
Toby Hunt, head of Guardian Water Treatment, looks at the impact of poorly managed and maintained HVAC systems on energy efficiency, focussing on corrosion, which causes system fouling ultimately leading to expensive repairs and possibly breakdown.
n our quest for efficient HVAC its essential that the fundamentals are covered. The most efficient and sustainable heating and cooling technology in the world is a waste of time if the associated pipework and components aren’t working well in support. Corrosion causes a number of issues in pipework and associated components that directly impact the efficiency of HVAC systems. Build-up of debris can lead to pumps working harder to maintain flow rates. Where corrosion debris has accumulated on heat exchangers and emitters, heat transfer is reduced and degradation to valve seats and pipework can result in flow irregularities and potentially leaks. All these problems create a system that is not working as it should, using more energy to operate, with a high risk of breakdown. In commercial buildings, most HVAC systems
are of the closed-circuit variety, so you would hope that if correct precautions are taken at the installation phase then corrosion should be kept at bay. Maintenance practices, or any time where there is intervention, can lead to oxygen ingress and other changes in the water make-up, which could then result in corrosion. With the cost of closed- circuit breakdown in large commercial buildings potentially running into the millions, this a problem that building owners and their FMs can ill-afford. Even if breakdown doesn’t occur, the potential
negative impact on efficiency can severely impact running costs and sustainability targets. With HVAC accounting for such a large proportion of energy usage in commercial properties, particularly ones where cooling is a priority (such as data centres), the knock-on effect of inefficient operations is potentially significant.
22 November 2021 What causes corrosion?
The main cause of corrosion is oxygen ingress, which can directly result in corroded pipes and parts, and/or create the right conditions for bacteria to thrive, leading to Microbial Induced Corrosion (MIC). There are of course other factors, but dissolved O2 is the main culprit. The trouble with this is that traditional means of checking closed circuit water condition (namely sampling) does not successfully detect for oxygen, just the signs that it is present – such as bacterial counts and dissolved metals. By the times these signs are present, the damage has already been done. A focus on bacteria is not always hugely helpful,
either. Most damaging when it adheres to the pipe, bacteria free flowing through the water (and likely to be detected by a sample) is not doing much harm. Once stuck to the pipe wall, there is a chance it can go undetected. Apart from causing corrosion, bacterial build-up can also contribute to reduced energy efficiency, creating slime that can restrict water flow and reduce thermal efficiencies. If humans are exposed to this bacteria, particularly the infamous Legionella, it can cause serious health complications. Thankfully, in a closed system at least, this is not so much of an issue. Corrosion can also be caused by the very
processes designed to prevent it. Flushing, using large volumes of water and chemicals, is employed during pre-commission cleaning and if a bacterial/ debris build-up issue has been identified. This process can weaken pipe walls, leading to further corrosion issues down the line.
Stopping corrosion before it starts
The ideal scenario is one where corrosion doesn’t have a chance to take hold in the first place. The key to this approach is having a true, real-time and continuous picture of water make-up, including all- important oxygen levels. This is a preventative approach that will lead to
reduced breakdown risk, fewer interventions and ultimately more energy efficient and sustainable closed-loop systems. We use real-time remote condition monitoring, which is fast becoming an industry staple thanks to recognition in BSRIA’s most recent version of BG29; its guide to pre-commission cleaning. A range of parameters, including the all- important oxygen, plus other measurements such as pressure, temperature and pH, are detected continuously, with alarms set for when conditions move out of ‘safe’ levels. With readings taken every 15 minutes, 24/7, there
is no room for error, no uncertainty, and no waiting for lab results, which means problems can be acted upon immediately and nipped in the bud. Flushing, therefore, is only used when it is absolutely necessary, not as a routine precaution. Monitoring in this way can be used throughout a
water system’s life – from pre-commission cleaning through to handover and ongoing maintenance – ensuring closed-circuit HVAC systems meet specification requirements and remain as efficient as possible. Corrosion is an issue, but with the right
preventative approach it’s one that can be potentially stopped before it even starts.
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