The "Heat extraction" research project is investigating the utilisation of heat from drinking water distribution networks in order to review the current state of knowledge and experience.
The utilisation of heat from drinking water distribution networks is becoming increasingly important as part of the energy transition and municipal heating planning. The possibility of extracting heat from drinking water was already discussed in the water sector a few years ago, but was rejected due to hygiene concerns. With the publication of the DVGW position paper ‘Heat utilisation from feeder, main and supply pipes of the public water supply’ in July 2024, the DVGW has initiated a reassessment of the topic.
The legal framework for the use of heat from drinking water is provided by Drinking Water Ordinance (TrinkwV) Section 13 (6), which states that energy utilisation systems that serve the purpose of operating the central water supply systems can be approved by the health authorities for a limited period of time. It is not possible to commercialise the energy obtained, i.e. to sell it to third parties via a district heating network.
The research project “Heat Extraction” aimed to systematize existing experiences and insights regarding the use of heat from drinking water and to conduct theoretical analyses of large-scale systems.
In the first part of the project, three existing heat utilization systems operated by German water utilities were analysed. These systems are designed for internal energy supply and each provides a thermal output of less than 100 kW. They extract drinking water from pressurized pipelines, recover thermal energy, and then return the water to the system. The applied technology – consisting of a heat exchanger, a low-pressure safety circuit, and a heat pump – proved to be technically feasible, although with a certain level of complexity.
In the second part, theoretical scenarios for large-scale systems were examined, in which the temperature of the entire drinking water flow was reduced by up to 5 K. Hydraulic simulations indicated that such heat extraction could lead to lower water temperatures at consumer endpoints, particularly in network areas close to the extraction point.
The results of the project can serve as a basis for considerations regarding the implementation of drinking water heat pump systems. Since the necessary expertise and simulation tools are available, corresponding risk analyses can be conducted and systemic utilization efficiencies can be determined. This enables a comparative assessment against alternative solutions.
