Fourth-generation DHC systems

DHC systems date back to the late 19th century but have undergone considerable changes and improvements since then. Many of the newest DHC systems are known as “fourth-generation” systems. They work at lower temperatures than the earlier generation systems, making them more efficient and lowering the related supply costs, because they can use lower-quality (lowertemperature) heat sources.

For a district heating system to be classified as a fourth-generation (4GDH) system, it must use smart integration to maximise the overall efficiency as well as the use of locally available renewable energy sources. A key feature of 4GDH systems is that they supply heat or cooling at temperatures as close as possible to the actual temperatures required by end users – a maximum of 60-70°C. Such relatively low supply temperatures (for heating) reduce losses in the district heating system and facilitate greater integration of waste heat sources (e.g. excess heat from data centres) than is possible using third-generation systems. 4GDH systems also use large-scale heat pumps of much higher efficiency to further exploit low-temperature waste heat sources or ambient heat. They may also use heat or cold storage to support the smart operation of heat pumps (Lund et al., 2021).

4GDH systems add major benefits; for example, they lead to low overall energy consumption and add flexibility to the power system. Compared with earlier generation systems, they have reduced grid losses by 6%, primary energy consumption by 4.5% and total costs by 2.7%.