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Wetenschappelijk en Technisch Centrum voor het Bouwbedrijf

19/08/2018

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The risk of legionella development in sanitary installations.

In order to determine whether it is possible to reduce energy use for domestic hot water (DHW) production and distribution, without increasing the risk of Legionella pn. development in sanitary installations, a full-scale test facility was built, consisting of a 200 liters water tank, a circulation system of nearly 40 meters long and 2 draw-off pipes. On a daily basis, a consumption profile corresponding to the DHW use of a single family (4 persons) was applied using two draw-off pipes, one corresponding to a kitchen and the other to a bathroom. Legionella pn. was cultivated in a separate water tank and then introduced into the test facility. In this test facility, applying different types of thermal shocks at 60°C (up to 2h) on a contaminated installation with a DHW production temperature of 45°C was not sufficient to keep Legionella pn. concentrations beneath 1000 cfu/l, in both the water tank and the circulation loop. Even daily shocks at 60°C were insufficient. After the thermal shocks the Legionella pn. concentrations reached 105 - 106 cfu/l within a couple of days. The expansion vessel, installed on the cold water inlet of the DHW production, proved to be an important source of recontamination of the installation after a thermal shock. Applying a weekly thermal shock of 24h at 65°C, in combination with regular draw-off during this shock on both draw-off pipes (of minimum 150s in this test setup), lead to stable Legionella concentrations <1000 cfu/l.

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