1.7 million Danish households have district heating. In other words, more than 64 per cent of all Danes have their heating supplied through the district heating network. A large amount of this district heating comes from small and medium-sized combined heat and power (CHP) plants, and according to the Danish District Heating Association the goal is to be CO₂-neutral before 2030.

The task of transforming the district heating sector into sustainable production is clearly considerable, and the time frame is very short. A new project being supported by the Energy Technology Development and Demonstration Programme (EUDP) will develop new infrastructure-ready district heating technologies for small and medium-sized district heating plants.

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"The project will develop a mature and sustainable system that is efficient, flexible, inexpensive and safe, and that can be used directly by e.g. CHP plants as a plug-and-play option. This is no mean task," says Assistant Professor Pourya Forooghi, who is heading Aarhus University's part of the project.

Two solutions to be examined

The project, which is called CO2MIX4Heat and is headed by the Danish Technological Institute, will develop two heat pump solutions, both of which run with natural refrigerants.

The first option to be developed will be an efficient and competitive dedicated CO₂ heat pump with air as the heat source. The heat pump uses non-toxic and environmentally friendly CO₂ as the refrigerant. Use of CO₂ makes it possible to lower the acquisition cost and maintenance costs – but without compromising on efficiency.

Models have shown that the efficiency of the CO₂ heat pump can be comparable to ammonia heat pumps if the design of the system and its components is optimized specifically for CO₂refrigerant. At the same time, the price is significantly lower, the environmental impact is minimized, and the footprint is significantly smaller.

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The second option to be examined is how zeotropic mixtures of natural refrigerants can be used to achieve even greater efficiency than is possible for CO₂ alone.

The project will build two test installations for research and a demonstration unit.

"Aarhus University's part of the project is to develop computer tools to predict and simulate how this new technology will work in practice. On the basis of these models, we’ll be able to optimise the entire system," says Pourya Forooghi.

The project is being funded by the EUDP with a total of DKK 9.3 million, and it has a total of seven partners: The Danish Technological Institute, Danfoss, Fenagy, Guentner, Aarhus University, The Danish District Heating Association and Vahterus. The project has a total budget of DKK 16.7 million and it started in January 2021. The project is expected to be completed in December 2023.