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Energy efficiency and hygiene in drinking water installations

EnEff:Wärme - Forschung für energieeffiziente Wärme- und Kältenetze
EE+HYG@TWI: New test rig for drinking water installations

New test rig for drinking water installations at the Centre for Energy Technology (ZET) at the TU Dresden: Extraction for one of the six residential units.

© TU Dresden

Technology summary

Software type Analysis, Balancing/Optimising
Term of project April 2014 - März 2017
Identification code EE+HYG@TWI
Key aspects

Project description

Initial situation and state of the problem

As the energy requirement values for space heating reduce, it is becoming increasing evident that, in regards to centralised domestic hot water (DHW) heating, the proportion of heat used for heating water is increasing relative to the total heating requirement for buildings. In addition, with centralised domestic hot water concepts, the supply temperature of the heating system is determined by generally recognised technical regulations for drinking water hygiene – geared to the species Legionella pneumophila. Performance requirements and the exergy level of the domestic hot water heating are therefore increasingly dominating the sizing of heat generators and the primary energy consumption during operation. This applies equally to both residential and non-residential buildings with domestic hot water requirements. The rigorous implementation and continuation of the LOW TEMPERATURE approach in the heating of buildings is thus failing in terms of the demands made on system temperatures on the hot water side in regard to health and hygiene aspects. The energy requirements for domestic hot water heating and circulation can still be reduced by measures such as hydraulic balancing, thermally insulating pipes, etc. However, the temperature and thus the energy level of the domestic hot water heating are much more decisive for the primary energy efficiency. Simply reducing the mean temperature by 5 Kelvin reduces the heat losses in domestic installations by 10 to 13 per cent. With district and local heating provision, the pro rata network losses for transporting the heat reduce in approximately the same magnitude. In addition, there are effects caused by increasing the electricity production by up to 6 per cent, such as with combined heat and power (CHP) systems with steam turbines. The coefficient of performance of heat pumps for heating domestic hot water can be increased by 20 % and the efficiency of solar thermal energy can be increased on average by 0.5 to 2%/K.

Project aims

The joint project has therefore set itself the following scientific and technological objectives, which are intended to be realised in interdisciplinary collaboration:

  • New insights through conducting comprehensive and simultaneous thermo-hydraulic and hygienic investigations and assessments of around 100 drinking water installations distributed throughout Germany and their comparison with the general statistics resulting from mandatory investigations made during the project period in accordance with the Drinking Water Ordinance in relation to Legionella spp. or Legionella pneumophila.
  • Quantifying the energy savings potential without using chemical disinfectants while verifying microbiological hygiene safety, in particular through comprehensive, targeted laboratory experiments with various generator technologies and new ways for adaptively, thermo-hydraulically balancing the circulation systems.
  • Use of new microbiological and molecular-biological analysis methods for assessing the quality of the heated and cold drinking water in hygienic and microbiological terms with regard to the parameters Legionella spp., Legionella pneumophila and Pseudomonas aeruginosa. Establishing the same aspects in the targeted assessment of the system condition and deriving measures.
  • Creation of new simulation tools for depicting the special thermo-hydraulic processes in the domestic hot water installation, taking into account the mutual interaction of installations for heated and cold drinking water. Use of experiments and practice monitoring for parameterising the simulation and validating the simulation results.
State of the implementation

With considerable communication effort and in compliance with data protection aspects, the operators and users of 80 buildings were successfully persuaded to participate in the field investigations. In what is a considerable enlargement of the standard scope of testing, a new sampling and testing scheme was developed and has so far been tested on 42 buildings. Initial results from the 24 fully investigated buildings show that problems are mainly caused by temperatures that are too high in the drinking water (cold). The major restructuring and expansion of the laboratory-scale test rig for emulating the drinking water installation of a 6-family apartment building and its furnishing with more than 160 sensors is completed. In two project meetings, the approach and interim results were discussed with representatives from Project Management Jülich (PTJ), the Scientific Advisory Board and the 9 sponsors from industry and associations, and the further course of the project was set.

International collaboration in IEA DHC Annex TS1

The EE+HYG@TWI joint project is integrated within the IEA DHC Annex TS1 “Low Temperature District Heating for Future Energy Systems” project framework. Annex TS1 is coordinated by means of workshops and other accompanying measures. These are organised and coordinated by Fraunhofer IBP in consultation and with the support of the coordinator of the joint project, whereby as a project partner Fraunhofer IBP is largely responsible for the communication at the international level.

  • IEA DHC Annex TS1