The systems that transport water around large, high-rise buildings need to comply with two key principles in order to maintain a high standard of hygiene – these are keeping the water moving and keeping it at the right temperature.
If either of these are compromised, the pipes could become a breeding ground for harmful bacteria which can then take hold within the water supply, with the worst-case scenario being the build-up of Legionella bacteria, which colonises in stagnant water between 20°C and 45°C.
In order to keep the water travelling through the pipes of a high-rise building clean and safe, the critical temperature zone between 20°C and 55°C must be avoided, otherwise there is potential for bacteria to thrive.
To make sure that the water reliably maintains a safe temperature, there are a number of factors which need to be considered:
– Layout: In a high-rise building, pipes carrying hot water should be kept separate from the pipes carrying cold water wherever possible in order to prevent unwanted thermal transfer between the two systems. If the hot water pipes and the cold-water pipes are installed in close proximity, the domestic cold-water pipes could be inadvertently heated to a temperature at which bacteria can proliferate.
It is also important that the domestic hot water is continuously circulated around the system. This re-circulated water returns to the water heater to be reheated, ensuring it stays above 55°C.
Should the water be allowed to lie dormant in the pipes for any length of time, it could lose its heat and stagnate at room temperature, potentially leading to a build-up of bacteria.
– Insulation: Pipework must be insulated to prevent unwanted temperature migration and to ensure the pipes meet the required thermal performance criteria as indicated by the relevant standard (BS 5422 2009). In the case of plastic materials, the thermal resistance value of the pipe can be added to the insulation’s value to give a combined resistance. This value will often show that using a plastic pipe will give an enhanced performance compared to metal alternatives.
Pipe coils that come pre-insulated are ideal for connecting the source direct to the outlet, as it means that every inch of the pipework is covered while avoiding the hassle of insulating the pipes after they’ve been installed. It also means that the insulation is covered with a constant, colour coded vapour barrier.
– Monitoring: As the hot water circulates, it needs to remain above 55 °C at all times. Even if the temperature only drops in one section of the pipes, it could still lead to the spread of bacteria, as the water continues to move around the system. To ensure that any issues are identified and rectified quickly, continuous monitoring of the water temperature is essential.
One of the most common causes of water stagnation is when an existing pipe system is repaired and lengths of rarely used pipework, known as ‘dead-legs’, or sections which are closed at one end but connected to the main network, known as a ‘blind-ends’, occur.
Both of these provide the opportunity for water to sit for long periods of time without being moved and should be removed from the system.
In systems that use traditional metal pipes, joints and connections can also pose a problem, as these can often have small crevices where water can sit.
A traditional metal system with a large number of joints can therefore increase the likelihood of the water becoming contaminated. There are piping products available which help negate this risk, such as Multi-layer Composite (MLC) pipes.
The press connections in the Multi-layer Composite system have no crevices and the flexible nature of these pipes means they can be navigated around obstacles to create a joint-free pipe system between the water source and the outlet.
In contrast, the rigidity and fixed length of traditional three-metre long stainless steel and copper pipes means that they require multiple connections.
Installing MLC pipes in a ‘loop’ style configuration will further minimise the chance of water sitting still for long periods of time.
Instead of simply sending the water to the outlet which has been opened, this type of system sends water through the whole local network, stopping water lying stagnant or lengths of pipework becoming redundant.
Making sure that water is able to keep moving while simultaneously staying at the necessary temperature is the only way to ensure that a high-rise building’s water supply remains safe and hygienic for the long-term.
Achieving this requires careful consideration of the design, installation and maintenance of the system from the outset of a project.
More careful consideration at the design stages can provide the project with a quicker more reliable installation whilst ensuring the building owners and occupants receive a heathy, reliable water supply which reduces operating costs and increases tenant wellbeing.
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