Solutions for avoiding risk of Legionella

Low temperatures in domestic hot water systems increases the risk of growth of Legionella bacteria which if inhaled can cause Pontiac fever or Legionnaires’ disease. Lund University, Kraftringen and COWI have worked on a report that investigates solutions for avoiding risk of Legionella when using LTDH. Kerstin Sernhed from Lund University (Dept. of Energy Sciences) introduces the report that you can download below.

What is the main purpose of the report?

As the district heating industry strives to lower the supply temperature in district heating systems in order to achieve higher system efficiency, new solutions might be needed for solving the problems of Legionella growth in the customers’ domestic hot water systems. This report aims to give an overview over possible different technical solutions to prevent Legionella growth in domestic hot water system. The report also aims to summarize the prevalence of Legionella cases in six countries (Sweden, Denmark, Norway, Finland, Germany and France) and compare it with the legislative framework within these countries regarding Legionella in domestic hot water systems.

Incidence of Legionnaires’ disease 2009-2015 in studied countries. Source: ECDC (2017b).

Incidence of Legionnaires’ disease 2009-2015 in studied countries. Source: ECDC (2017b).

What are the main findings in your studies?

The review of national rules regarding Legionella safety in domestic hot water (DHW) systems shows that the legislation in all countries is based on maintaining a sufficient temperature in domestic hot water systems in order to make an unfavourable environment to the Legionella bacteria. There are no rules that deal with the control of bacterial levels of Legionella in the water.

Our overview over feasible technical solutions for preventing Legionella growth in domestic hot water systems shows that there are several alternative techniques that theoretically could prevent Legionella growth. Many of these methods, however, come to short because they cannot be viewed as completely safe or as good long-term solutions, or they have not been commercialized and fully tested yet. Because of the legal temperature requirements in domestic hot water systems, today’s legislation does not support ultra-low supply temperature (with a supply temperature of 50 °C) in district heating grids in most EU countries unless the DHW temperature in the customer installation can be boosted using local heating solutions.

In some countries the “three-liter-rule” is applied for small domestic hot water systems. This rule says that if the volume of water in the system from the entry point to the tap is not more than three liters, then the temperature requirements can be disregarded. More research looking at Legionella safety in these systems still needs to be done testing different temperature levels. But if the research can show good results, there will be reason to argue for some legal changes. Today’s legal requirements in DHW systems can then be seen to unnecessarily aggravate possible system efficiency in the district heating business that comes with lower supply temperatures.

What happens now?

Now we are going to look at how the regulations on temperature levels in domestic hot water systems affect our DEMO sites in Lund in Sweden and Høje-Taastrup in Denmark, and see what possibilities we have to test some technical solutions on Legionella safety within the project.

Read the report

The report is uploaded under Reports and Documents on the following link: Report on solutions for avoiding risk of Legionella

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