REnewable Low TEmperature District (RELaTED) provides a demonstrated concept of ultra-low temperature network solution for new district heating systems and the progressive conversion of currently running district heating systems in order to de-carbonize energy supplies in urban environments.


District Heating (DH) systems are identified as key systems to achieve a de-carbonized supply of heating energy in European Cities, as they allow the efficient integration and balancing of various sources of renewable and waste heat sources with high levels of efficiency and economies of scale. Yet, DH systems only correspond to a market share of roughly 12% of the EU heating market today. To increase that number, innovative solutions and technology demonstrations are needed to pave the way for expanding and modernizing existing DH networks, as well as introducing and establishing DH systems in emerging EU markets.

One way to achieve this evolution is by reducing the heat intensity in districts with the progressive transformation of the building stock to Nearly Zero Energy Building (NZEB) standards, with Positive Energy Buildings being increasingly common. Low (LT) and Ultra-low (ULT) temperature district heating (DH) systems present fewer technical constraints to incorporating low-grade heat sources. Also, they operate at substantially lower costs due to fewer heat losses, and better energy performance of heat generation plants, which is further improved by the use of de-carbonized energy sources at low marginal costs. In the process to substitute present DH networks with LT (50-55ºC) and ULT (~45ºC) DH systems, critical issues such as treatment against legionella, adequacy of heat delivery systems, or methods to directly inject RES into the district energy network need to be solved.

RELaTED aims at solving these issues by providing a demonstrated concept of ultra-low temperature network solutions for new district heating systems and by implementing the progressive conversion of systems already in operation.

What are the actions foreseen by the project?

  • RELaTED will be demonstrated in four different DH networks comprising different countries, climates and network scales (Denmark, Estonia, Serbia, Spain).
  • 2 regional studies will be performed to assess the feasibility of the introduction of ULT DH in two Central and South EU regions.
  • In the transition to the RELaTED ULT concept, conversion route maps and hybrid schemes will ensure successful conversion of DH systems already in operation, by progressive ULT conversion of subnetworks, and main heat distribution infrastructure, guided by progressive conversion of substations for each consumer, to ensure continuity of service.
  • Energy planning processes will allow the selection of suitable urban areas for the integration, extension and/or development of new ULT DH networks, with better cost/benefit scenarios.

The project interacts with an array of other EU-funded projects focusing on developing sustainable heating and cooling solutions in Europe.

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No 768567. The sole responsibility of this publication lies with the author. The European Union is not responsible for any use that may be made of the information contained therein.

In the news

Upgrade of the DH network in Iurreta reaches its turning point

With the upgrades in distribution and piping constructed to a large extent, Iurreta will see its heating system stopped this week to modify its operational principles & adapt it to the RELaTED Ultra Low Temperature DH concept.

New project building on the results of RELaTED

The RELaTED project partners Inaventa Solar has recently started a new project, DisolBat (distributed solar and “blue batteries”), which builds on the results of its international collaboration with RELaTED.

New solutions for heating to test ULTDH in Spain

The Swedish manufacturer NIBE recently sent to Spain some specially developed heat pumps and hydraulic modules that will contribute to transforming a DH network into a ULT network. These components and solutions will heat and cool 2 buildings in a corporate building complex in the RELaTED demonstration site of Iurreta, Spain, owned by the Basque Government.

An innovative solar system to be installed in Spain

The solar collectors from Inaventa Solar will deliver energy for heating and domestic hot water to a building complex owned by the Basque Government, in one of the demonstration sites of the project RELaTED.

EnergyFlexHouse – Energy Neutral Concept House to Test Solar Collectors and District Heating

The EnergyFlexHouse help test technologies of Solar collectors and reduce the operational cost associated with energy loss and at the same time make the systems “greener” without large investments in the frame of RELaTED.

RELaTED in Celsius talk on low temperature heating systems!

The RELaTED project was showcased during Celsius Webinar on Low temperature district heating!