Low temperature district heating and cooling networks are a promising technology to reduce the energy consumption on one of its top demand sectors: buildings.

AUTHOR: Antonio Garrido Marijuan, researcher in RELaTED.

This article was previously published in the September 2021 issue of Celsius newsletter.

The main objective of the RELaTED project (financed by the European Union’s Horizon 2020 research and innovation programme under GA-768567, www.relatedproject.eu) is to develop those concepts that path the way to the massive uptake of highly optimised, low-temperature networks that provide heating and cooling at the district level, the so-called 5th-generation district heating and cooling (5GDHC). This includes new solar systems easily integrated at building level developed by Inaventa (https://inaventasolar.com), innovative substations that optimize multi-directional flows between renewable energy systems, buildings and the DH grid developed by Metrotherm, and optimized, DH integrated heat pumps for both heating and cooling, developed by NIBE.

To further develop and improve these innovative concepts, 4 pilot sites are at the core of the project, including locations in Denmark, Estonia, Serbia, and Spain. The three former are already delivering promising results, with large sets of data currently under analysis. In the latter, commissioning of the new systems is being carried out at the time of publishing (actually I am simultaneously answering emails with last-minute issues as I write this article).

Besides the time-consuming troubleshooting, RELaTED’s pilot sites are success stories. The problems with the implementation of the demos include (of course) COVID-19, but also other issues common-to-all-large-installations: permits, delays, lack of financing, etc.

On the successful side of the story, the RELaTED project team has recently reached an important milestone, the commissioning phase of the Spanish demo. The close cooperation between the Basque Government (owner of the pilot site) and Fundacion Tecnalia Research & Innovation has ensured a proper implementation together with the work of the rest of the consortium. This article shows the main aspects of the implementation.

Iurreta’s pilot site

The demo case in Iurreta consists of a complex belonging to the Basque police, with 13 buildings previously served by two gas boilers connected to a heating network and several distributed heat pumps (cooling). This pre-existing network was working under suboptimal conditions and relied on fossil fuels.

Aerial view Iurreta (Related)

Figure: aerial view of Iurreta’s pilot site

The RELaTED project proposed the renovation of this network based on the following:

  • Energy modelling of the complex to find the most promising points for the reduction of energy consumption.
  • Installation of a distribution ring at ultra low temperature (35ºC) working in parallel to the pre-existing network.

Figure: Last installation works for the low temperature ring’s collector.



Figure: Overview of the DesignBuilder model of one of the buildings of the DH network and results from the simulation of the two boiler productions and the total capacity of those. It can be observed that the total nominal power is seldomly reached in both scenarios simulated.

  • Installation of distributed, reversible water/water heat pumps, DH connected, allowing decentralized & demand-driven energy supply. The heat rejected from these heat pumps in reversible mode is injected to the DH during summer periods, preventing energy waste by a bidirectional flow as a 5GDH feature.

Figure: Reversible heat pump connected to the low-temperature ring.

  • Injection of low-grade renewable heat through the deployment of a solar thermal system building integrated, typical from 5GDH.
  • Monitoring of the different flows to support innovative control, matching the availability of low-grade sources (excess heat from heat pumps, solar energy availability) to low-grade demand (pre-heating of DHW, swimming pool) at all times, as expected from a 5GDH.
  • Data analysis of the monitored data to further improve the operation of the system.

The conclusions from the operation of this complex are yet to be investigated and should come out soon.