Transformation in Flensburg: low temperatures for efficient heat pumps 

3 min read

As an innovative public utility company, Stadtwerke Flensburg is committed to decarbonisation and CO2 neutrality. To achieve this goal, the municipal utility company is working with Gradyent to reduce temperatures in the district heating system. As part of the partnership, the two companies have found a way to reduce the necessary annual heat share with a temperature above 95°C from around 10% to 1%. This means that heat pumps can be used to a higher extent and operated efficiently. 

The Vision for a Greener Future 

Stadtwerke Flensburg aims to become “green and digital” and thus CO2-neutral by 2035. The company is working hard on projects for CO2-neutral energy production to meet the requirements of federal funding, which provides state support for decarbonisation in the district heating sector. 
The central aspect of Flensburg's transformation and decarbonisation plan is the integration of a high number of heat pumps into the urban district heating system. To make this possible and increase the efficiency of these heat pumps, the temperatures in the district heating network must be significantly reduced.

A Common Path 

The transformation plan was developed as part of the BEW Module 1 “Transformation Plans and Feasibility Studies” funding program of the German Government. Stadtwerke Flensburg has been working with Gradyent since January 2023 and commissioned the company to build a Digital Twin and simulate temperature reduction.  

Gradyent offers district heating system services based on its Digital Twin platform and cooperates with some of the most innovative district heating companies in Europe. The services include simulations and real-time operational optimisation based on a proprietary Digital Twin that combines physical modelling with AI. One such partner is Stadtwerke Flensburg, which supplies around 100,000 residents with district heating and covers over 90% of the city's heating needs.

At the beginning of the collaboration, Gradyent created a Digital Twin that mapped the 1 TWh district heating system of Flensburg in detail. During this time, the Gradyent team worked closely with various areas of Stadtwerke Flensburg, including the generation and network business areas.  

The network division manager and the employees responsible for the transformation plan provided valuable input in terms of data and network knowledge. On this basis, Gradyent created a Digital Twin of the entire Flensburg district heating system and trained it with the available historical data. 

The Result: Significantly Reduced Flow Temperatures 

Gradyent worked closely with Stadtwerke Flensburg to define how temperatures in the district heating network can be reduced using the Digital Twin. In addition, Stadtwerke Flensburg identified additional investment measures to take further steps towards even lower temperatures in the district heating network. 

In the course of the collaboration, ten transformation scenarios were created to cost-effectively reduce the proportion of heat transported above 95°C from around 10% to 1%. This will significantly increase the economic efficiency of heat pumps in the future.  

In the first step, the proportion of temperatures above 95°C is reduced from 10% to around 3% on an annual average through the optimisation logic of the Digital Twin. Over the year, this means an average temperature reduction of 10°C. The proportion of heat above 95°C is then reduced to less than 1% through further investments in pipes and pumps. This way, Stadtwerke Flensburg can reduce heat losses and increase the efficiency of heat pumps. 
Thomas Räther, Head of Networks at Stadtwerke Flensburg, is satisfied with the partnership: “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.” 

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