Legionella-distribution temperature

In central systems that produce hot water with storage for domestic purposes, in order to prevent the proliferation of dangerous Legionella bacteria, the hot water must be stored at a temperature of at least 60°C. At this temperature it is certain that the proliferation of the bacteria that cause Legionnaire’s disease will be totally inhibited.

These temperatures, however, are too high for direct use by the user; water at these levels can cause severe burns. It is therefore necessary to reduce the temperature of the hot water distributed to the user to a lower value suitable for use.

Moreover, not only the storage but also the entire distribution network requires thermal disinfection at regular intervals. Otherwise the bacteria would develop quickly in there too.

In view of the above, it is therefore necessary to use an electronic mixing valve able to:
· reduce the temperature of the distributed water to an adjustable value which is lower than the storage temperature
· keep the mixed water temperature constant despite any variation in inlet temperature and pressure, or in the drawn-off flow rate.
· allow programming thermal disinfection with a higher temperature than the adjustment value, in the necessary time and in periods with less frequent consumption (nighttime).

Thermal disinfection

The adjacent diagram shows the behaviour of Legionella Pneumophila bacteria as the temperature conditions of the water containing the bacteria vary, in laboratory cultures. To ensure correct thermal disinfection, it is necessary to go up to values of no less than 60°C.

The product

The electronic mixing valve is used in centralised systems that produce and distribute domestic hot water.
Its function is to guarantee and maintain the temperature of the domestic hot water delivered to the user when there are variations in the temperature and pressure of the hot and cold water at the inlet or in the draw-off flow rate.
This particular series of electronic mixing valves is equipped with a specific regulator that controls a set of programs for circuit thermal disinfection against Legionella.
In addition it enables checking the temperature and time for thermal disinfection are actually reached and undertaking the appropriate corrective action. All the parameters are updated every day and logged, with temperatures recorded every hour.
Depending on the type of system and habits of the user, it is possible to program temperature levels and operation times in the most appropriate manner.

In addition, it is fitted for a monitoring and remote control connection.

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