How warm is your cold? Fighting legionella in water systems

legionella in water systems

Steve Hunt, MD of Steven Hunt & Associates, discusses the need for industry experts to stay up to date with new technology in order to tackle the issue of legionella developing in ill-equipped water systems

Hospitals are increasingly conscious of the methods needed to prevent the development of legionella in water systems. However, their increased knowledge is creating problems, to an unmanageable extent.

Recently, efforts have been made to ensure that the circulation temperature of hot water remains above 50c-55c, depending on which legislation is consulted.

Thermal balancing and other solutions have been a mixed bag but generally there’s been an improvement, which has been measured by the implementation of temperature sensors in pipework.

Similar techniques have also been introduced into cold water systems, where it’s expected to maintain temperatures below 25c. To most ‘authorised personnel’, the discovery of warm cold water has been a real eye-opener, as it appears that the more you look, the worse it is.

Hospitals are large, complex sites, which over the years have adapted and extended. As such, infrastructure is adapted to accommodate the changing uses, the original engineers’ calculations are lost in the changes and once systems have been altered over three times, they develop a life of their own.

Hospitals are often serviced from multiple plantrooms to cope with vast sites, but systems are still large, meaning pipework can travel miles around a building.

The rules state that water should be circulated above 55c. Generally, hot water will leave a plantroom at temperatures in the region of 65c. However, given the length of some systems, it’s not surprising that by the time it reaches the furthest outlets, heat loss can leave the circulation water short of the minimum requirement.

The hot water pipe isn’t one long pipe; it has a secondary, smaller pipe running in parallel so that hot water is always circulated around a circuit. In theory, this is sized to offset the heat loss to sustain temperature.

However, when new circuits are added, existing pumps are expected to take the additional load and there’s only so much spare capacity that a pump can accommodate.

In the past, if a hand basin was removed due to refurbishment, the pipework would often be blanked off in the ceiling, leaving dead legs of stagnating water, which naturally reach temperatures promoting legionella growth.

There isn’t an NHS trust that would now allow such practice but there was a time when this did happen, and it’s hard to imagine that all of the dead legs in hospitals have been identified and removed.

It seems that when changes are undertaken, there’s insufficient effort to ensure that record drawings are kept up to date.

Some trusts still have original linen drawings and this can be a problem, as contractors are only interested in providing information relating to the works that they have undertaken, with it being impossible to update original linen drawings.

The implementation of BIM will provide a much better platform for recording up-to-date information, or at least this is what we currently believe.

Our operations are always changing and following the rise in MRSA, significant effort has been made to improve infection control, with one of the measures taken being the introduction of more hand wash basins.

While such measures help to reduce the risk of transmission, they have had a significant impact on systems, with basins sitting unused for many hours during the day.

Fresh water contains oxygen which can leave the fluid at high temperatures, forming bubbles that find their way to the highest point in the system and lodge. If too much air is locked into high points without sufficient means for expulsion, air locks can hinder flow.

How many times have we seen pipework overlap in a crowded ceiling void, creating the ideal spot for air locks and challenging the flow to individual appliances?

This therefore means that in nearly every case a flow and return pipe will need to be branched in to the main infrastructure to accommodate an appliance, increasing the balancing issues and the oversized pipework problems highlighted above.

While it’s important to keep hot water hot to avoid legionella, there’s also a need to keep cold water cold for the same reason. Allowing water to warm up can lead to the threshold for legionella growth and this creates a problem that hasn’t been recognised until recently.

So, what are the answers to all of these issues? HTM 04-01 (2016) has recognised the issue of warm cold water and makes the suggestion that cold water services should be installed in a different ceiling space to other heat sources. How this can be achieved in a hospital environment? Only they know!

Complex mixing valves with automatic flushing devices that periodically discharge a quantity of water to waste have been used extensively. However, while this maintains decent flow and avoids stagnation, it impacts on the energy bill and is a sheer waste of portable water.

Valve manufacturers have designed ‘plug and play’ balancing valves that can be fitted to every branch. They monitor water temperature, allowing water to circulate if the temperature drops below a set point.

Often the distribution water is insufficient in temperature in the first place, resulting in all the valves being open, which is worse than a manually balanced system as water travels through the shortest route and will not flow to the extremities of the system. Some valves also require a minimum water pressure to operate satisfactorily and in old systems this can’t always be provided.

Cold water circulation systems have been tried while working on the same principle as the hot water with limited dead legs, but even with circulation, without draw-off water, the temperature will still rise and some designers have even introduced mechanical cooling to tackle this.

Long term, NHS trusts need to recognise that we can’t keep building on old existing systems and adapting. They also need to make sure that when new systems are installed, old systems are stripped out, any changes are properly recorded and pipework is labelled so there’s no ambiguity in the future. For their part, manufacturers need to do more to explain their products in more depth, as some are technically brilliant but implemented poorly.

Technology now sits at the forefront of our industry when it comes to water implementation as we continue to search for the perfect solution to banish germs. I believe we’re now on the brink of reaching a happy medium, with industry experts now more informed than ever about the need to keep fluids at the perfect temperature.


Steve Hunt

Managing Director

Steve Hunt Associates

Twitter: @stevehuntassoc

LinkedIn: Steven A Hunt & Associates

Facebook: stevenhuntassociates


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