Supply of domestic hot water at comfort temperatures without legionella
The target of this project was to provide optimal solutions for handling legionella problems in different low temperature domestic hot water systems.
The problem of legionella in hot water systems arises, when constructing low temperature district heating systems. To achieve low temperature district heating, the supply temperature of the district heating water will be lowered from around 75 ° C to around 55 ° C. However, that will boost the risk of legionella in domestic hot water. The most favorable temperature interval for legionella to live is 25-50 ° C. Therefore creating an appropriate solution for the legionella problem should be given the priority in order to secure safe supply for the consumers and to realize low temperature district heating.
In this project, multiple factors - such as the building type, the system volume, whether renovation were involved, the structure of heating system etc. - were taken into consideration. Analysis of economic performance were also be included, so that a comprehensive solution can be provided. Techniques on the cutting edge of district heating and water treatment will be involved as much as possible.
The main scenarios and their potential solutions are shown in the following:
- It is expected that the supply temperature of district heating system can be reduced from the current 75° C to 65° C without any legionella problems. Therefore, it is viable to lower the district heating supply temperature down to 65° C without changing the existing system. This can be considered as the solution during transition period. The safety and the energy performance of this solution will be tested.
- For small volume system, based on German Standard W551, temperature is never a limitation for applying low temperature district heating. Therefore, to restrict the system volume to under 3 liters is a proper solution for small-volume system, such as single family house. Economic and energy performance will be analyzed based on temperature decrease mainly.
- For large volume system to be renovated, for example multi-story buildings, the solution, is to divide the whole system into several separated systems, so that the volume of each part can be limited to under 3 liters. Therefore, legionella is inhibited by small volume. Technique such as flat station can be applied for system separation. The inhibiting effects and energy performance as well as the economic viability will be analyzed.
- For large volume system without renovation, thermal, chemical or physical treatments should be applied. Comparisons of the efficacy, the installation and operation, the limitation and the investment were investigated and documented in a conference paper. The selection of optimal treatment could be different case by case.
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Review of various soltuions for avoiding critical leves of legionella bacteria in domestic hot water system by Ph.d. Fellow Xiaochen Yang
Presentation at the 8th Conference on Sustainable Energy Systems, Dubrovnic, Croatia 2013
Review of various soltuions for avoiding critical leves of legionella bacteria in domestic hot water system by Ph.d. Fellow Xiaochen Yang
Article in presedings from the 8th Conference on Sustainable Energy Systems, Dubrovnic, Croatia 2013
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