Analysis and development of necessary measures for lowering the domestic hot water temperature in low-temperature supply systems

The continuous improvement of building energy standards and the expanding use of low-temperature systems lead to decreasing flow temperatures in terms of space heating. In the course of this development, domestic water heating is becoming increasingly important with regard to the total heat demand in the building. In view of the energy transition, there are great opportunities for CO2 avoidance. In Germany, the decarbonization potential in the area of domestic water heating is around 36 million tons per year. Innovative approaches to decentralized domestic water heating with reduced system volumes promise the exploitation of optimization and savings potential. In combination with low-temperature systems, the obstacles to the expansion of renewable energies in the building sector are further reduced. However, a major challenge in the implementation of domestic water installations in the low-temperature range lies in the assured avoidance of hygienic hazards caused by pathogenic microorganisms, which prefer to multiply in the temperature range between 25 °C and 45 °C. Other factors such as the supply of nutrients and the presence of bacteria also play a role. Other factors such as nutrient supply, residence time and flow velocity also influence the concentration, which must be balanced.
The project “Trans2NT-TWW” addresses these opportunities and challenges. The identification and analysis of necessary measures for the targeted reduction of the domestic water temperature in order to hygienically ensure the increased use of regenerative-based domestic water heating in low-temperature systems is the core objective of the four-year project. Due to the potential energy savings and the possibility of coupling with low-temperature systems, the focus of the investigations is mainly on decentralized domestic water heaters in different system configurations.
The project is divided into three phases. The first phase includes a simulation study of practically relevant systems for decentralized domestic water heating. Selected transformation measures of centralized and decentralized supply systems are compared. A multi-criteria analysis allows the evaluation of the simulation results on the basis of technical, economic and ecological parameters. The verification of the practical suitability is part of the second phase. For this purpose, representative demonstration buildings will be equipped with measurement technology and monitored over a period of 2 years. Of particular interest are the transformation-related energy savings and the hygienic quality of the drinking water. The third phase serves to create a guide-line, which contains an evaluation matrix with all relevant evaluation aspects. On the basis of this, different user groups are to be supported in selecting individually suitable low-temperature systems for hygienic domestic water heating. The project itself and the guide continue to serve the dissemination of hygienically safe low-temperature systems and generally improve the normative framework of the recognized rules of technology.