Converting District Heating: From Conventional To Ultra-Low-Temperature District Heating

Although lowering the temperature of district heating is not a new idea, it is only recently that lower temperatures have become the perfect solution because the technology has now matured. This was the backdrop to a demonstration project which Sweco carried out in collaboration with AffaldVarme Aarhus (AVA) for the Danish Energy Agency. The purpose of the project was to test the concept which Sweco Denmark had developed in collaboration with the Technical University of Denmark (DTU) and Danfoss in the area of large-scale ultra-low-temperature district heating.

Facts

Customers: AffaldVarme, Aarhus (AVA), Danish Energy Authority

Period: 2013–2015

Location: Geding, Denmark

Description

The project involved converting the existing conventional district-heating system in the small town of Geding outside of Aarhus to an ultra-low-temperature system where the supply temperature from the central unit was to be lowered from 70°C to 45°C. The temperature level at the central unit was set so that consumers would always have a minimum supply temperature of 30°C.

As this low temperature is not sufficient for hot water for domestic use, however, the initial phase, part-funded by the Danish Energy Agency, involved the installation of a district-heating unit with a small built-in heating pump unit in each dwelling. This made it possible to raise the district-heating temperature so it could produce hot utility water. At the same time, the temperature of the hot utility water no longer depended on the supply temperature of the district heating water in the main distribution system.

The district-heating unit with the small built-in pump unit, a so-called microbooster, was developed by Danfoss, the Technical University of Denmark and Sweco Denmark as part of an EUDP project which concluded in 2013. At present, four microboosters are installed in Birkerød and these microboosters are an improved version of the microbooster installed in Geding in the summer of 2014, where all dwellings have been converted, a total of 25 houses.

Concurrently with this project, Sweco Denmark has prepared a plan for phase 2 for AVA. This will involve replacing the existing centrally located oil-fired boiler, which produces heat for the distribution system using a combination of solar heat, heating pumps and energy storage. Geding will not only be fossil free, but also fuel free.

Customer quotes

"This project has enabled us to run the system at somewhat lower temperatures than we would have done otherwise, and it ultimately means that it will improve the project economy, because a lower temperature level means less loss of heat. Geding is what you might call a small town with a relatively high rate of heat loss (around 54% in 2014, dispersed over the entire year), which has now been reduced to 39%, or a 30% reduction."
Jørgen Krum, Line Manager, AffaldVarme Aarhus.
"We have generally become more focused on lowering the temperature to a minimum within the technical provisions which govern us, whereas we previously tended to operate with a wide margin. It is easier to try to reduce the temperature all the way in Geding, however, because the residents are aware that technical difficulties can arise as part of the demonstration project."
Jens Rishøj Larsen, Works Manager, AffaldVarme Aarhus.

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