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By Lars Gullev, Managing Director VEKS and Chairman of DBDH THE COLUMN
DISTRICT HEATING - MORE THAN 100 YEARS OF HISTORY, BUT STILL RAPIDLY DEVELOPING
This issue of Hot Cool highlights • how US and Canadian universities are converting district heating systems from steam (1st G DH systems) to hot water (3rd G DH systems), thus reducing the heat loss, for example to between 33% and 50% of the current loss. • how in Copenhagen, Denmark, the last of the original steam system, established from 1906, is converted to hot water, so that the total district heating system in Copenhagen in 2021 will be a 3rd G DH system. • how in Albertslund, Denmark, the first projects to convert the current 3rd G DH system have now been launched so that the entire municipal district heating system in 2026 will be a 4th G DH system. • how existing district heating systems in older buildings can be converted from 3rd G DH systems to 4th G DH systems. I hope this issue of Hot Cool can create inspiration for the further development of district heating everywhere - whether the district heating systems are developed from 1st G DH systems to 3rd G DH systems or from 3rd G DH systems to 4th G DH systems. The important thing is that we always make sure to communicate to politicians and the public that well-run district heating systems allow the utilization of vast energy resources, which without a district heating systemwould be lost to our society. Furthermore, district heating systems facilitate renewable energy to be utilized on a large scale for the economic benefit of citizens and society. That is the Christmas present that we in the district heating sector can give to everyone. Thank you for a pleasant 2016 and welcome back to an even more exciting 2017 – happy new year!
The first steam-based district heating systems were put in commission in the 1880s in the United States. The systems are today known as 1st G (generation) DH systems, and it was steam that was the energy transferring medium in the district heating systems until around 1930. At that time, water took over, and the flow temperature was reduced from the present more than 200 degrees C to about 120 degrees C - we had now started the 2nd G DH systems. In Denmark, we began to see the first heat accumulators as part of the district heating systems - primarily in order to provide greater flexibility in the operation of the CHP plants that produced district heating for the transmission network. The next major development leap within district heating technology occurred in about 1980, when pre-insulated district heating pipes replaced steel in concrete channels. The 3rd G DH systems were born. The flow temperature of the district heating network was lowered, which meant that the heat loss was also reduced. Renewable energy began to contribute to the production of district heating - partly in the form of biomass replacing fossil fuels, but also the construction of large solar plants, which began supplying heat into the district heating network, took place in more and more countries. The flow temperature had now been lowered to 70 -90 degrees C. We have now addressed the 4th G DH systems where the flow temperatures are as low as 50-60 degrees C. This low temperature level means that the heat loss from the pipes is further reduced, but what is most important is probably the fact that low temperatures enable a use of energy resources in the community that was previously lost – most prominently the utilization of waste heat from the industry. Furthermore, the potential is increased for utilization of renewable energy on a large scale - for example by utilising solar heat which can be seasonally stored in large heat storages for use in the winter. A flow temperature of 50-60 degrees C is low, but test district heating systems are already conducted where the water temperature is as low as 35-50 degrees C, so the development certainly has not come to a hold yet.
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