Legionella
The invisible danger for the hygiene of drinking water
We view hygienically safe drinking water as a matter of course. But contamination due to legionella is becoming increasingly common. Legionellae are microorganisms that multiply through longer retention times and at temperatures between 25 °C and 55 °C. They multiply faster when water in pipes and at extraction points is left to stagnate for a long time. In showers with mist nozzles, they can become hazardous to health and cause respiratory illness.
For hot water, worksheet W 551 put out by the German Technical and Scientific Association for Gas and Water or DVGW requires a temperature of 60 °C for hot water tank outlets and a minimum temperature of 55 °C for circulation.
But in practice, far less attention is paid to DIN EN 806-2, which stipulates that cold water should not exceed 25 °C. In its worksheet “Information WASSER Nr. 90”, the DVGW even recommends keeping temperatures below 20 °C, since legionellae are seldom detected under these conditions. But with more and more building insulation trapping heat in the installation areas, cold water temperatures of over 25 °C are increasingly common.
Wilo has developed solutions for both cases to ensure that the critical temperatures of 55 °C for hot water and 25 °C for cold water are maintained.
Domestic drinking water circulators and systems minimise the risk of legionella, making an important contribution to water hygiene.
Domestic hot water
Supporting thermal disinfection
Our domestic hot water circulators prevent stagnation by ensuring the drinking water system is continuously circulated. In fact, they prevent the conditions required by legionella to develop in the first place. The pumps promise maximum convenience by immediately supplying all water taps in the building with hot water the moment you need it – no more waiting for the shower to run hot in the morning, for example. What’s more, the pumps automatically detect what is known as the boiler’s “legionellae switching” and increase their speed to ensure that the entire domestic hot water system undergoes thermal disinfection.
The following products support thermal disinfection:
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Wilo-Star-Z NOVA
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Wilo-Stratos PICO-Z
Cold drinking water
Circulation and regular water exchange
Including a circulation line in a cold water installation keeps the water permanently moving to prevent stagnation. This effectively stops the spread of pathogens.
Wilo’s response to this challenge is the system solution called Wilo-SiFresh, which monitors water temperatures and reduces the temperature in the pipeline system by flushing if it exceeds a predefined limit value. The use of an additional cooling device enhances this effect, allowing the temperature to be reduced to below 20 °C.
Compared to decentralised solutions, centralised flushing and water extraction with Wilo-SiFresh takes far less time and minimises the amount of water used for hygienic flushing.
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