Energy and water are crucial to almost all HVAC systems, and preserving these resources, which, if wasted, impact sustainability goals, should be a priority for all building owners and maintenance teams. Poorly maintained water systems can negatively impact energy usage, by causing pipe corrosion and system fouling for example, and the very processes that keep these components clean can lead to large volumes of water wastage.
Getting the balance right is a challenge, particularly where UK cooling demand is so high, at 10% of the total electricity usage, and only set the rise – more than tripling by 2050 according to estimates. Commercial buildings are the biggest electricity using culprits, including manufacturing facilities, offices and critical healthcare facilities.
The state of the water inside closed HVAC systems in particular can be hard to gauge. It is estimated that around 50% of commercial buildings have hidden problems with their HVAC systems that could be contributing to increased energy demand – anything up to 40% of total usage.
Buildings waste water from the outset
The construction, handover and ongoing maintenance of large commercial spaces wastes water. Pre-commissioning cleaning, for example, an essential element of new water system hand over, accounts for half of all water usage when a building is built. Cutting corners during this process, however, is a false economy - if not carried out effectively, repairs and breakdown will cost more in the long-run
Water wastage occurs when large volumes of water are used to flush the system, removing debris and maximising flow rates. Following flushing, biocide washing and chemical cleaning is used to remove bio-films and surface deposits, creating a stable surface more likely to withstand corrosion, backed-up by a corrosion inhibitor to further prevent damage. Finally, there’s back flushing, with yet more water used to remove any last remnants of debris.
When it comes to the design of a water system, correct construction is essential. Systems must be pressurised properly throughout the 24/7 cycle and expansion capacity needs to be specified correctly, alongside system pressures. Once the right foundations have been laid, these parameters must be maintained over the system’s lifetime.
How can water wastage be reduced?
There are ways to reduce the volumes of water used in precommission cleaning – advanced filtration, for example, can dramatically reduce the amount of water required while still ensuring that debris is sufficiently removed. This approach also cuts cleaning times, saving water and reducing time on the job when compared with traditional methods.
Monitoring is also key during this process, with a real-time indication of system condition, including the parameters that can be indicative of future corrosion issues. Microbiological activity must also be checked for, allowing for prompt and pre-emptive treatment adjustments.
Beyond pre-commissioning cleaning
There are a number of parameters that real-time monitoring can detect, allowing action to be pre-emptive and more likely to stop major issues in their tracks. Managing pressure, for example, an important task throughout a water systems life, identifies oxygen ingress. If system pressures exceed the baseline, water losses may occur, requiring fresh, aerated water to top up the system. If pressures get too low, air could be sucked into the system. Dissolved oxygen is a contributing factor in almost all types of corrosion.
By having a continuous handle on pressure and other elements that make up water condition – such as pH, temperature and galvanic currents - as soon as potentially corrosive conditions are flagged up, steps can be taken immediately to stop corrosion in its tracks. While chemical inhibitors can help, they should be considered a secondary line of defence.
Continuous monitoring may also go someway to reduce flushing overall, checking, for example how quickly conditions return to in-specification conditions when unavoidable disruption takes place. In the past, a sample would’ve been taken at this point that would most likely have shown contamination, resulting in flushing. Monitoring can demonstrate when the issue is resolved, often with no intervention at all.
This is just one example of where monitoring can also reduce site visits – another contribution to sustainability. With data accessed remotely from any internet device, interventions can be planned and reactive call outs reduced. Overall, this approach will lead to a reduction in emergency repairs, unnecessary disruption and unsafe situations.
The open system cooling conundrum
Balancing energy consumption and water wastage in open loop systems, such as the large cooling towers used to keep data centres the right temperature, arguably the most important infrastructure asset of the 21st century, can be more of a challenge. Water plays a leading role in these systems, chosen because it is the most efficient cooling method at scale, using around 40% less electricity than the alternatives.
There can be no compromise when it comes to ensuring data centres are running smoothly, but that does not mean that steps cannot be taken to improve sustainability. Water recovery and rainwater reuse can dramatically cut wastage recycling about 70% of water and saving huge amounts of money. Savings equate to approximately £2 per cubic metre of water recovered, which turns into big figures in some of the largest data centres. We commonly see the initial outlay of a water recycling system recouped in less than six months.
Water recycling systems also clean the water, sometimes making it cleaner than when it first entered the system.
A sustainable future
From construction to handover and throughout a water systems life, balancing operational certainty with efficiency is a major challenge of our age. Thankfully, the latest HVAC management techniques that focus on having a true picture of system condition, with action based on real need, not guess work, are having a positive impact on both resource conservation and whole life costing. Coupled with a focus on recycling and reuse, commercial buildings can make strides to reduce their carbon footprint at every stage – ‘sustainability’ means more than just a focus on headline grabbing renewables.