Photograph of the Maria Laach heating plant in Austria. Behind the plant a green landscape stretches out and there are fluffy clouds in a line across the blue sky.
The biomass district heating plant Maria Laach am Jauerling serves as Austrian demonstration site for the Flexi-sync project. Photo: Flexi-Sync

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District energy utilities and property owners can both benefit from the optimisation of demand side flexibility, for example by investing in thermal storage and buildings with both district heating and heat pumps. This article is based on a webinar within the ERA-NET SES project Flexi-Sync and describes the approach taken in the project to enable the optimisation of district energy flexibility. 


Improve efficiency and balance the energy system at the same time!
In the district energy networks, there are many ways to utilise cost-effective flexibility. However, it is a challenge to optimise these more complex systems. The Flexi-Sync project is developing a service for making use of district energy flexibility and optimising heat grids and heat control in buildings.

The value of district energy flexibility

As the energy system is experiencing a transition to a more sustainable system, the share of variable, renewable energy is increasing and the demand for electricity, heating and cooling is becoming more inconsistent. At the same time there is an increasing number of connections between the electricity grids and the thermal grids, such as combined heat and power plants (CHP), heat pumps, electric boilers producing heat and buildings with several heat sources. There is a great availability of cost-effective flexibility in the district energy networks – even more than in the electric networks. This offers an excellent opportunity for the district energy systems to improve the efficiency and to balance the connected energy system. However, this also requires that certain challenges are managed. Firstly, it is necessary to have a system perspective and tools to manage complex optimisation problems. Secondly, collaboration between several parties and new business models for flexibility are required.


Model based optimisation and machine learning forecasting

As flexibility adds an extra degree of freedom to the optimisation problem, traditional control logic is hard to apply when trying to optimise district energy flexibility. Therefore, model-based optimisation is a possible approach. With this option, a digital twin is created. Thanks to the recent developments of powerful tools, more complex optimisation problems could be solved. It is even possible to optimise with regards to probability (e.g. confidence intervals for weather, heat demand and electricity price).

Predictions of the heat demand is an important input for the optimisation of flexibility in district energy networks. The demand forecasting can be done in different ways. Energy signature – energy demand as a function of outdoor temperature – is a fast and scalable method but offers low precision as there are more factors than outdoor climate influencing the heat demand. On the other end of the spectrum is a manually created physical model representing a building or a heat grid. This may offer high precision but is very time consuming. It is also unique for a specific object and therefore hard to scale.

A third method is demand forecasting with machine learning. Machine learning enables more parameters than outdoor climate to be taken into consideration – for example calendar parameters (time of day, day of week, holidays, etc). The machine learning algorithms are also self-learning, implying that they are “smarter” than humans. For example, the EnergyPredict tool used in the Flexi-Sync project can reduce errors with 85 percent compared to more simple demand forecasting methods, such as energy signature, while still being fast and fully automated. In Flexi-Sync, forecasts are delivered for energy, flow and temperatures, on district energy grid level all the way down to individual substations. The predictions are based on historical, actual demand that has been used as a training data set for the self-learning algorithms.


Optimisation of flexibility in Flexi-Sync

About the Flexi-Sync project

The Flexi-Sync project is an ERA-Net SES financed project focused on achieving flexible energy system integration using concept development, demonstration and replication. The project gathers 16 partners from four EU Member States: Austria, Germany, Spain and Sweden. Six demo sites in the countries will participate. The project period runs from 2019 to 2022.

The Flexi-Sync project is an ERA-Net Smart Energy Systems project and part of the 2018 RegSys call. The objective is to identify how flexibility in district energy can be optimised and, thereby, contribute to the balancing of energy systems with increased shares of variable renewable energy supply and fluctuating demand. As part of this, a new service is being developed which combines district heating optimisation and demand control (see Figure 1).

The service is built upon two existing platforms supplied by two of the partners within the project. The Flexi-Connect API will connect the two existing services and enable the transferring of information and control signals. The district heating optimisation will receive information on the available building flexibility to use in optimisation and the demand control of the buildings will receive a control signal to control the demand for optimal efficiency from a system perspective. This will lead to savings for both the district heating utility and the property owners.

An illustration of the service Flexi-Connect.

Figure 1: Flexi-Connect API

In Flexi-Sync, operational demand side flexibility is added to the district energy systems participating in the project. In the case of the Swedish and Austrian demonstrators, presented in the webinar, the demand side flexibility consists mainly of thermal storage and buildings with both district heating and heat pumps. The thermal storage enables heat demand to be shifted in time, and heat pumps in buildings with district heating make it possible to alternate between heat sources. This use of resources for flexibility are among the elements that will be optimised within the project. The district heating utilities and housing companies will be connected to the service that is being developed and the optimisation of the district energy systems will be continuously improved throughout the project (from 2019 to 2022).

Text by:
Anna Nilsson (IVL Swedish Environmental Research Institute)
Johan Kensby (Utilifeed)

Contacts and additional information:

The system optimisation and related services in the Flexi-Sync project are a part of the Utilifeed platform, which is a cloud-based platform that fundamentally changes the way district energy companies work with design, analysis and optimisation across their whole value chain. For information on what is currently available from the project, as well as the roadmap ahead, contact Johan Kensby (CTO, Utilifeed), or visit

The flexibility extraction and active demand side management is part of the NODA Heat Network solution package. NODA creates AI-based content in the digitalisation of energy systems. For more information about the NODA network, please contact Christian Johansson (CEO, NODA Intelligent Systems) or visit





Impact areas

  • Greater share of renewable energy

  • Reduced costs

  • Reduced climate impact

  • Reduced climate impact


Anna Nilsson (IVL),
Johan Kensby (UTILIFEED), e-mail
Christian Johansson (NODA), e-mail

External website

External links:

  1. ERA-Net SES website 
  2. A webinar on Flexi-Sync can be viewed here: Webinar registration

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