Fraunhofer Institute for Building Physics IBP
Fraunhofer Institute for Building Physics IBP

District Heating from Wastewater for Supplying the Ultra-Low-Energy Urban District Neckarpark

Site plan of the Neckarpark urban district
© LHS
Site plan of the Neckarpark urban district showing the heat exchanger in the sewer system, the central heating plant, and the two heating networks.
Installed heat exchanger in the wastewater sewer
© LHS
Installed heat exchanger in the wastewater sewer – construction phase 2018.

Since 2013, the new urban district Neckarpark has been developed on the site of the former freight yard brownfield in Stuttgart-Bad Cannstatt. Municipal wastewater serves as the primary energy source for the district heat supply. Its thermal energy is harnessed via a heat pump system and distributed through a low-temperature district heating network.

To increase the efficiency of the district heating network, developers were required from the outset to significantly exceed the statutory energy performance requirements for new buildings (minimum standard: KfW Efficiency House 55). At the launch of the project and for several years thereafter, the Neckarpark project - with a thermal extraction capacity of 2,100 kW from wastewater - was by far the largest wastewater heat recovery project in Germany. As such, Neckarpark serves as a nationwide benchmark for sustainable energy supply in urban districts.

Project goals

The project aims to achieve highly energy-efficient buildings and a heat supply system largely powered by locally available energy sources. The original goal of fully covering the heat demand exclusively via heat pumps using wastewater could not be achieved, as the district became increasingly densified during the planning and implementation phases, resulting in significantly higher domestic hot water demand. Consequently, the energy concept was expanded to include combined heat and power (CHP) units and peak-load boilers.

Status of the project

The Neckarpark research project demonstrates that large-scale use of wastewater heat at the district level represents a technically reliable, economically viable, and environmentally sound solution for supplying heat to new urban developments.

Within the project, the heat supply concept was optimized and further developed, planning activities were supported, and both planning and implementation processes were accompanied by defined quality standards. Various operator models were also evaluated. Developers and users were provided with information on improving energy efficiency through multiple communication channels.

In addition, a monitoring program based on the guidelines of the Federal Ministry for Economic Affairs and Energy (BMWE) research initiative “Energy Transition in Buildings” was developed, and the corresponding monitoring infrastructure was installed and tested. Initial monitoring results were collected, and measures for operational optimization were implemented. The insights gained from design, planning, implementation, and operational optimization were consolidated into a practical guide, enabling their transfer to similar projects.

Project partners

  • City of Stuttgart (Office for Environmental Protection)