Both Swedish and international rules and guidelines on Legionella are based on work carried out by the UK HSE (Health and Safety Executive). The temperature range for possible growth of Legionella bacteria in water is generally between 20-45°C, so tap water should ideally be kept either above 50°C or below 20°C. Legionella dies at temperatures above 60°C, and hibernates at temperatures below 20°C. In practice, the growth rate is so low at temperatures up to 25°C that, for example, Safe Water states that cold water temperatures up to and including 24°C (within 8 hours) are okay for pipe shafts containing hot water circulation (HWC). The time scale for significant Legionella growth in water systems is days to weeks at temperatures >24°C.
During showering, the Enduce floor drain heats the incoming cold water to a temperature between 30-35 °C just before the preheated cold water is mixed into the shower mixer and flushed out of the shower head. At the end of showering, the heat exchanger and pipes cool down rapidly (<3 h) to a temperature <25 °C and therefore neither temperature nor residence time is sufficient for Legionella growth in or around the Enduce energy recovery floor drain. Cooling time and temperature have been verified by independent tests at RISE after showering at 40 C and cooling at room temperature.
The floor drain installation instructions clarify that underfloor heating must not be placed on the heat exchanger space of the floor drain to completely avoid the risk of Legionella growth.
For example, the Enduce floor drain is safer from a Legionella perspective than common pipe shafts with insulated pipes for cold water and hot water circulation.
Learn more about Legionella and how to minimize the risk of problematic Legionella levels in drinking water systems here: https://www.hse.gov.uk/pubns/priced/hsg274part2.pdf
