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17. Nov 2015 - Hygienically safe and energy-efficient provision of drinking water

EE+HYG@TWI: Detail showing the heating cable (orange in 6-clock position) and the fibre optic distributed temperature sensing system (green in 12-clock position) before being insulated

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Photo: TU Dresden


Neubau und Sanierung im Gebäudebestand führen zu einem sinkenden Energiebedarf für die Raumheizung. Damit steigt der prozentuale Anteil der Trinkwassererwärmung (TWE) eines Gebäudes jedoch an. Dessen Wärmeverluste zu senken ist deshalb besonders wichtig. Dies gilt für Wohngebäude und Nichtwohngebäude gleichermaßen. Das Problem: Bei Konzepten der zentralen TWE ist die Vorlauftemperatur des Heizungssystems von den allgemein anerkannten Regeln der Technik zur Trinkwasserhygiene vorgegeben. 

In view of these energy and hygiene requirements, the scientists and practitioners in the “Energy efficiency and hygiene in drinking water installations (EE + HYG @ TWI)” joint research project have examined how hygienic safety and energy savings can work in conjunction. Although measures such as hydraulic balancing and thermally insulating pipes can significantly reduce the energy requirement for drinking water heating and circulation, the temperature level is much more decisive, however, for achieving energy efficiency. Simply lowering the mean temperature by 5 Kelvin reduces the heating 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 domestic hot water heating can be increased by 20 per cent and the efficiency of solar thermal energy can be increased by an average of 0.5 to 2 per cent per Kelvin.

Tasks and goals of the joint research project

The joint project intends to demonstrate that such potential energy savings can also be realistically achieved during plant operation. They are intending to demonstrate this by conducting, amongst other things, thermo-hydraulic and hygienic investigations of around 100 drinking water installations distributed throughout Germany and then comparing them with the results of mandatory legionella investigations. Various generator technologies shall be evaluated and new ways tested concerned with the adaptive, thermo-hydraulic balancing of circulation systems. This enables the energy savings potential to be determined in greater detail – and this without the use of chemical disinfectants for verifying the microbiological hygiene safety. In addition, the researchers want to use new microbiological and molecular biological analysis methods for assessing the water quality.

Current state of the investigations

The scientists have so far developed and tested a new sampling and analysis scheme for 42 buildings of different types. Initial results from the 24 fully investigated buildings show that problems are mainly caused by temperatures that are too high in the cold drinking water. In addition, the researchers designed a laboratory-scale test rig for emulating the drinking water installation of a 6-family apartment and its furnishing with more than 160 sensors. It has now been fundamentally restructured and expanded. The EE+HYG@TWI research project runs until March 2017.

More information and all research partners can be found on the project’s business card “Energy Efficiency and Hygiene in drinking water installations”.

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