EUDP (Danish Energy Technology Development and Demonstration Programme) project “Legionella protection and energy efficiency for installations and supply” carried out from September 2020 to February 2023:
The project group:
Søren Anker Uldum, Statens Serum Institut (SSI)
Henrik Kjeldsen, Danish Technological Institute (project responsible)
Tommy Steen Møller, The Project office - Region Zealand
Kaj Bryder Danish Technological Institute (project responsible)
Leon Buhl, Danish Technological Institute (project responsible)
Nikas Arp-Wilhjelm, KAB
Hagbard Clausen, Danish Clean Water (DCW)
Ditte Andreasen Søborg, VIA University College
Torben Schifter-Holm, METRO THERM
Carl Hellmers, Fredericia Fjernvarme
ground to a considerable extent. Regarding energy efficiency and the possibilities of using alternative energy, both energy systems need to have water temperatures as low as possible. There is thus a significant temperature-related dilemma about ensuring Legionella-safe domestic water installations while simultaneously meeting the need to save energy, use renewable energy sources, and reduce the climate footprint. An interdisciplinary project co-financed by the EUDP (Danish Energy Technology Development and Demonstration Programme) has investigated this dilemma and pointed to some solutions. The diverse group of partners has included the Danish Tech- nological Institute and Statens Serum Institut (SSI, under the auspices of the Danish Ministry of Health). The project included partly a literature study on previous investigations and requirements for Legionella in domestic hot water and the derived energy consumption, partly developing and demonstrating three measures for control of Legionella in domestic hot water installations. These were, respectively, a tool for risk assessment of Legionella (Danish Technological Institute), an electric booster for monitoring and ensuring the necessary water temperature (METRO-THERM), and an innovative solution for biocide dosing (Danish Clean Water). Responsible partner is shown in brackets. Results from the literature study The study was based on a major literature search followed by contacts to selected knowledge and research centers. The
study included an examination of the influence parameters affecting the spread, growth, and reduction of Legionella, as well as of authority requirements, standards, and guidelines. The study showed that due to especially biofilm, the temperature requirements for controlling Legionella are often underestimated, and the Danish temperature requirements and practices are often challenging about Legionella. The study also leads to the following conclusions: It is generally agreed that Legionella pneumophila develops at temperatures higher than 20 - 25°C and lower than 45 - 50°C. The Legionella will die at 50°C and higher temperatures in the water. Due to, e.g., biofilm formation, it is at varying temperatures, however, often uncertain if the necessary temperatures have been obtained in the biofilm, although fulfilled for the water. An overall water temperature of 50°C or above will normally limit the Legionella content to the recommended max. 1,000 CFU/L (Colony Forming Units per Liter). However, these temperatures are particularly challenging for energy efficiency, climate footprint, and running costs as the necessary comfort requirement for the water temperature is only 45°C. Besides the water temperature and the biofilm, several other parameters impact the growth/reduction of Legionella, such as water flow conditions, water quality, pressure, and affected materials. However, the study showed that the knowledge of the conditions influencing the growth and reduction of Legionella is often relatively poorly founded or
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