LIFE4HeatRecovery network 2: RELaTED Project

RELaTED is a project coordinated by TECNALIA which involves 11 partners. The project has received funding from the European Union’s Horizon 2020 research and innovation Programme under grant agreement No. 768567.

Like LIFE4HeatRecovery, RELaTED is involved in the decarbonisation process with the use of low-temperature waste heat and renewable energy to be integrated in district heating networks.

More than 50% of the population of Latvia, Denmark, Estonia, Lithuania, Poland, Sweden & Finland is served by DH networks.

District heating (DH) systems are one of the most energy efficient heating systems to deliver heat in urban environments, with proven reliability within many decades already. DHs are also identified as key systems to achieve the decarbonisation of heating energy in European Cities. Renewable and waste heat sources are foreseen at the same time as decarbonised heat sources and the way to guarantee competitive energy costs with limited influence of fossil fuel supply price volatility. Despite this fact, district heating are serving to a market share of only 12% of the European citizens today, when studies have shown that these systems can be expanded to a market share of 50% in 2050. Such ambitious scenario requires a conversion of actual DH concept. In the forthcoming energy market, DHs need to evolve regarding:

  • The reduction of their operation temperature to integrate low-grade industrial heat sources.
  • The introduction of larger shares of renewable energy sources.
  • The introduction of distributed heat sources (reject heat from cooling equipment…).
  • To guarantee economic viability with the trend of DH heat load reduction due to the evolution of Near Zero Energy Buildings.
  • District heating systems are identified as key systems to achieve the de-carbonization of heating energy in European Cities.

Ultra-Low Temperature concept

RELaTED proposes a district heating concept where substantially lower temperatures are used.

RELaTED will provide an innovative concept of decentralized Ultra-Low Temperature (ULT) network solution that can pave the way for expanding and modernizing existing district heating networks as well as introducing and establishing district heating in emerging EU markets. This project, funded under the European Union’s Horizon 2020 research and innovation programme, aims to develop a robust ultra-low temperature concept, which allow for the incorporation of low-grade heat sources with minimal constraints. Also, ULT DH reduces operational costs due to fewer heat losses, better energy performance of heat generation plants and extensive use of de-carbonized energy sources at low marginal costs. The RELaTED ULT DH concept will be demonstrated in four complementary operation environments (new and existing DH, locations, climatic conditions, dimension…) in Denmark, Estonia, Serbia and Spain.

RELaTED will provide an innovative concept of decentralized Ultra-Low Temperature (ULT) network solution with substantian efficiency and environmental benefits.

RELaTED approach will follow the strategy of the electrical smart grids, in which energy generation is decentralized and consumers evolve to prosumers (they consume and produce energy).

DH network concept

Expected results

RELaTED proposes a DH concept, where substantially lower temperatures are used in the DH network, with substantial efficiency and environmental benefits such as:

  • Increase the operational efficiency of heat production.
  • Incorporate renewable energy sources; reject heat, industrial waste heat, combined heat and power production.
  • Reduction in the final cost of heat due to lower distribution heat losses.
  • Reduction of Greenhouse Gas Emissions and air pollution.
  • Develop a heat price system, which allow integrating variable energy price schemes.


Considering the complexities and particularities of each district heating (DH), RELaTED concept is being implemented in four different DH networks covering extremely different climatic conditions, construction traditions, urban density, pre-existing district scheme, ownership and energy services contract schemes:

  1. Large district heating network, in Serbia.
  2. New urban development, in Denmark.
  3. Operational district heating, in Estonia.
  4. Corporate district heating network, in Spain.

Four demostration sites are foreseen


RELaTED will integrate present technologies into a new ULT DH concept, at distribution temperatures below commercially operative DH networks today.

District heating substation technology

3FSs allow buildings to operate without local storage and to integrate buildings as distributed heat sources in the DH network.

Heat pums technology

District heating integrated renewable heat pump system will be integrated with the DH networks as its primary heat source, at sensibly constant temperatures at 30-45ºC, depending on connection pipe of the primary loop.

Building integrated solar thermal systems technology

RELaTED will integrate two ST collector as components of the Building Integrated Solar Thermal (BILTST) solar loop. These are differentiated by their aesthetics and their geographic suitability:

  • Glazed ST collector system. All-polymeric solar collectors demonstrate aesthetic integration into the building envelope, overcoming existing installation barriers and reducing overall costs at the building site.
  • Unglazed ST collector system. The unglazed ST collector is integrated into a highly customizable architectural envelope in terms of aesthetics and integration into  architectural projects.