Flensburg Stadtwerke: low temperatures for efficient heat pumps  

3 min read

Stadtwerke Flensburg is an innovative public utility company that supplies around 100,000 residents and covers over 90% of the city's heating needs. The company is committed to achieving CO2 neutrality by 2035.  

On its path to decarbonisation, Stadtwerke Flensburg partnered with Gradyent to reduce temperatures in the district heating system.  

The partnership resulted in a reduction of the required annual heat share with a temperature above 95°C from around 10% to 1%. This allows for more extensive use of and improved operation of heat pumps that are part of Stadtwerke Flensburg system.  


Stadtwerke Flensburg is engaged in projects focused on CO2-neutral energy production to meet the requirements of federal funding schemes supporting decarbonisation in the district heating sector.  
The central aspect of Flensburg's transformation and decarbonisation plan is the integration of multiple heat pumps into the urban district heating system. Smooth integration and increased efficiency of heat pumps calls for lower temperatures in the network. 

To achieve its goals, Stadtwerke Flensburg commissioned Gradyent to build a Digital Twin of its heating network and simulate temperature reduction scenarios.   



The network division manager and employees responsible for the transformation plan offered valuable input around data and network. Using this foundation, Gradyent created a Digital Twin of the entire Flensburg district heating system and trained it with the available historical data.  


We were looking for a suitable partner and Digital Twin for more than eighteen months. Gradyent presented itself as the best provider for us, both in terms of Digital Twin technology and district heating expertise. Together, those aspects made the difference, and in retrospect, it was exactly the right decision. 

Thomas Räther
Head of Networks at Stadtwerke Flensburg


The Digital Twin allowed the company to create ten transformation scenarios for cost-effectively reduction of the proportion of heat transported above 95°C from around 10% to 1%. 

First, the proportion of temperatures above 95°C would be reduced from 10% to around 3% on an annual average via the optimisation logic of the Digital Twin. Over the year, this translates to an average temperature reduction of 10°C. The proportion of heat above 95°C would then be reduced to less than 1% through further investments in pipes and heat pumps.  

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