[LglPrev21] Legionella prevention

The function is used in hot water systems to prevent the growth of the legionella bacteria or as a thermal disinfectant to kill legionella.

Legionella are pathogenic bacteria. Legionella grow in warm water at temperatures of approximately 20 °C to 50 °C. Disinfection or killing legionella bacteria depends on temperature and time. They begin to die off at around 55 °C.

As a consequence, the hot water temperature must be increased daily or weekly for a specific time to disinfect. A scheduler exists in the scheduler to send a time pulse to start the function.

The function must be activated via time pulse. Hot water is heated to the legionella disinfection temperature during a defined period. The function succeeds and is canceled if the temperature remains above the disinfection temperature for the required duration. An alarm (LglPrev'Failed) is generated if conditions are not fulfilled during the required duration.

The state of the function is indicated on function block State:

1 - Off

2 - In progress

3 - Successful

4 - Not successful

5 - Time slot expired

Key

TTnkTop	Tank temperature, top
TTnkBtm	Tank temperature, bottom
Sp	Setpoint
Dmd	Storage tank charging control
SupyTI	Supervision time. The temperature must be above the setpoint during this period. Set on TiMon, e.g., 60 minutes.
ValCirPu	Request to the circulating pump
LglPrevAct	The function is active, and the conditions are not yet met.
Timer	Timeframe for maximum duration, e.g., 4 hours
LglSched/Timer	The time pulse from BSchedule triggers the function. During the timeframe timer, the temperature must be higher than the setpoint for an adjustable time. The function is then fulfilled.

See also

• Predefined I/Os
• Trend types
• Module families