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HVAC glossary
Legionella (disinfection) cycle
A legionella cycle periodically heats the cylinder water to a higher temperature to reduce the risk of bacteria.
Legionella are bacteria that can multiply in warm, stagnant water. A heat pump produces hot water most efficiently at lower temperatures, so the controller provides a disinfection (legionella) cycle: at a chosen interval the cylinder water is heated to a higher temperature.
- The cycle frequency, temperature and duration are set in the controller at commissioning.
- The cylinder’s electric immersion heater often helps reach the higher temperature, so the cycle is scheduled, for example, at night.
- The cycle increases electricity use, so its settings should be justified, not arbitrary.
- Hot water system hygiene also matters: avoiding long dead-leg pipe branches, and circulation.
Mitsubishi Electric ECODAN controllers have an integrated legionella prevention function. Our specialists configure it at commissioning according to the cylinder type and your usage and explain how it works.
If hot water is not used for a long time, for example while you are on holiday, it is worth discussing the cycle settings with our specialist.