THE ANTI-LEGIONELLAE CIRCUIT: A SIMPLE WAY OF HEAT TREATING PIPES TO KEEP LEGIONELLA AT BAY

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1 THE ANTI-LEGIONELLAE CIRCUIT: A SIMPLE WAY OF HEAT TREATING PIPES TO KEEP LEGIONELLA AT BAY Organisations involved Gemeinnützige Wohnungsfürsorge AG München (GEWOFAG), a non-profit housing association in Munich, Germany Description of the case Introduction Legionellae bacteria are ubiquitous in the aquatic environment in natural water as well as in artificial water systems. In the drinking water supply systems they occupy niches suitable for their growth, such as stagnant water where biofilms can develop and where water temperatures are suitable for legionellae growth (e.g., certain parts of domestic water supply systems, cooling towers, and whirlpool or spa baths). Central hot water supply systems are especially at risk of contamination by legionellae. One method of preventing legionellae growth is thermal disinfection, which is a reliable process irrespective of water quality. But this method requires a great deal of energy, which means it is expensive. In addition, the water used is so hot that it may pose a risk of burns to users of the system, and can also increase corrosion in the piping system. For those reasons Wilfried Ebster, who works for GEWOFAG, developed a special method of treating water systems to get rid of Legionella bacteria. GEWOFAG is a non-profit housing association that manages more than 30,000 homes. Prevention of legionella in drinking water supply systems has become an increasingly important issue for building and real estate companies as well as for hotels, hospitals, and nursing homes. Housing associations must ensure high quality drinking water which requires high maintenance standards. Relatively large piping systems with large boilers are at high risk of contamination by legionellae or other microorganisms because of the increased likelihood that some of the water will become stagnant, and that water temperatures will reach C providing ideal conditions for these organisms. In 1995 Ebster, advisor for research and development at GEWOFAG, began searching for a solution to prevent legionellae growth in these systems. His objective was to develop a solution that would be suitable for new installations as well as older ones undergoing renovation. Following the German regulations DVGW (German Technical and Scientific Association for Gas and Water) W 551, W 553 as well as the VDI (Association of German Engineers) No. 6023, GEWOFAG wanted to develop a simple and inexpensive method to prevent legionella contamination of the drinking water supply system. The main objectives of the regulations mentioned above are to avoid: temperatures that promote microbiological growth pipes with dead ends stagnation of water in pipelines oversizing of pipeline systems Aims The basic idea was to eliminate legionella by thermal disinfection but avoiding costly installations and scalding risks to the users. The aim was to develop a simple and economical method of preventing legionella growth in water supply systems.

2 3.3. What was done, and how? Ebster developed the anti-legionella circuit system, which is controlled by a three-way valve that permits the length (path) of the water pipe to be varied and hence ensures safe and economical legionella prevention (Picture 1). Picture 1: The anti-legionella circuit. One of the most critical areas in the hot water piping system with regard to legionella growth is the hot water storage tank beneath the heat exchanger close to the fresh water supply pipe. Water in this area forms layers at different temperatures: hot water moves up and cold water remains at the bottom. Unfortunately the temperature sensor is often placed in the upper part of the tank, in the hot water layer, and does not warn about ideal growing temperatures for legionella in the lower area of the tank. To make matters worse, biofilms (thin layers of microorganisms that may form slime on surfaces in contact with water) are able to develop here, and they provide an ideal environment for legionella growth. The anti-legionellae circuit focuses on this part of the piping system. It consists of two threeway valves. One regulates the division of the hot water flow and the other allows for regulation of the heating circuit (Picture 1). The first three-way mixing valve controls the hot water flow from the heating source into the central drinking water heater and thereby regulates the temperature in this tank (Picture 1, no. 3). The central drinking water tank is connected to a hot water pipe system, from which any desired number of tapping points can be branched off (Picture 1, no 4). The water temperature in the return line of the circulation system (Picture 1, no 5) is at least 55 C (return temperature), when it flows into the central drinking water heater. The second three way-valve (Picture 1, no 11) is connected to the return line and can divide the drinking water conduit into two streams. One stream flows into the middle of the tank via a first balancing valve and the other flows into the bottom of the tank via a second balancing valve (Picture 2). 1. Position A-C is the normal position of the three-way valve allowing the hot water to circulate through the whole system: maximum circulation distance supply to the user. 2. Position B-C opens a short cut. The hot water circulates through a short pipe for a relatively short period, whereby the temperature is raised (Picture 2). The volume of this short cut does not exceed 3 litres. The short cut allows an economic thermal disinfection of the central drinking water heater. The water layers are mixed and no different layer temperatures in the tank are observed.

3 The disinfection of the warm water supply system should be carried out monthly, but it can be done more frequently if required. Picture 2: Division of the water flow through two control valves. This method allows the water temperature to be raised in a cost-effective way: when the valve is put into the short cut position for disinfection, the temperature in the heater/storage tank is raised to at least 65 C. Hot water passes only, or mainly, through the short cut, stirs up the thermal layers in the tank, eliminates microorganisms, in particular legionella, and prevents the formation of biofilms. An advantage of this form of thermal disinfection is that the hot taps can still be used during the process. However, the system will now allow quite hot water to reach the taps of the end users. GEWOFAG therefore implements special measures to prevent scalds. Hot water can be dangerous and may cause quite severe burns and scalds. For that reason special prevention measure had to be implemented: Installation of thermostatic mixer taps for each single tapping point (the safest solution for the end user), Carrying out thermal disinfection at night from 2 o clock to 3 o clock a.m. (According to GEWOFAG, water consumption is very low between 2 and 3 a.m). Corrosion of the piping system can be avoided by carefully selecting the plumbing material. Basic precondition for an effective anti-legionella circuit is the proper insulation of the whole drinking water system, in order to avoid heat losses and the warming up of the cold water pipes (Picture 3). Picture 3: Three-way-valve of the short cut and circulation pump, presented by its developer, Wilfried Ebster.

4 3.4. What was achieved? Development of an anti-legionella circuit system Prevention of legionella growth in hot water supply systems of the GEWOFAG housings Unproblematic refitting of old hot water systems Promotion of a cheap and energy saving method to prevent legionella growth Setting up of a website providing information about legionella and the anti-legionella circuit system ( Success factors The anti-legionella circuit (warm drinking water conduit system) is a simple and easy method to prevent Legionellae growth in a warm water drinking pipeline. Mr. Ebster, who developed the anti-legionellae circuit, won in 2006 the Federal Award for Excellent Innovatory Developments in Crafts (Bundespreis für hervorragende innovatorische Leistungen für das Handwerk). The patent is registered under DE C2. The anti-legionellae circuit has been successfully tested in the GEWOFAG facilities in Taufkirchen in 2000 (picture 4) and has been used since then in more than 3,000 GEWOFAG locations. The simple construction and low cost of the installation of the anti-legionella circuit are its main success factors. The circuit is made of commercially available components and it can easily be installed in new buildings or added to existing systems in older ones. The antilegionella circuit is practically maintenance free. Picture 4: The anti-legionellae circuit has been used successfully in the GEWOFAG facilities in Taufkirchen since 2000.

5 3.6. Further information Wilfried Ebster, Kirchseeoner Straße 3, Munich Tel. ++ (0) , Transferability The anti-legionella circuit is a very simple method of preventing legionella growth in domestic water supply systems. It can be easily installed and also easily added to older systems. The components are commercially available. The method can be easily transferred to other countries Abstract An anti-legionella circuit is mounted to a hot drinking water supply system connected to one or more heater/storage tank(s) for hot water. A hot water short cut operated by a three-way valve allows the circulation temperature in the critical areas of the hot water system (in particular beneath the water heater/storage tank near the fresh water pipe) to be increased to 65 C for short periods, Through this innovation the tank can be thermally disinfected in an energy-saving way and the water can be kept largely free of microorganisms. References, resources: Contact information: Wilfried Ebster Kirchseeoner Straße 3, Munich 1. Ebster, W., Legionellen in der Trinkwasserinstallation, GEWOFAG, 2004, 2. United States Patent, No. US B1, Sept. 14, 2002, Warm Drinking Water Conduit System, 3. GEWOFAG, Patentierte Legionellen-Schutzschaltung, website, accessed in Sept. 2009, 4. Ebster, W. personal communication, 2009