The ever-increasing demand for electricity to power the many new data centres represents a significant challenge to the global transition to a green energy system. The electricity consumption for these large data centres in Denmark is expected to be about 3600 GWh annually in 2025, which will generate a large amount of surplus heat. Excess heat from data centres should thus be collected for reuse. The energy efficiency of a data centre can be calculated by using a so-called PUE model = total power drawn / power drawn by IT equipment. Older data centres have a PUE of over 2, as do new ones with water and air cooling. The most efficient data centres, which are located in colder climates, use free cooling. Their PUE values are around 1.1 to 1.5. This value, then, must continue to drop, while energy reuse must rise.

Solution idea

The best-known alternative to air cooling is water cooling, which reduces the total power consumption of the data centre’s servers by 10-30% compared to air cooling. The difference is greatest in geographical areas where outdoor temperatures are high. However, another alternative to avoid water cooling exists — inside the electronics themselves. Heatflow ApS has developed a two-phase cooling technology (a thermosiphon), specially designed to passively cool data centres’ servers with the same high efficiency as methods like water cooling. With it, power consumption can be reduced and heat can be reused.

In this project, Heatflow, together with AAU ET and R&R Consult, will develop a new capacitor to improve overall system efficiency. In doing so, it will make the utilisation of excess heat, which the two-phase cooling technology effectively removes from servers in data centres, much more attractive for use in district heating systems.

Problem owners


Project timeline

PHASE 1: Conceptualisation
PHASE 2: Development and testing
PHASE 3: Demonstration and validation
PHASE 4: Commercialisation

Financed by


Start: November 2020
End: December 2022
Grant: DKK 1.225.000

Contact person

Hans Jørgen Brodersen

Hans Jørgen Brodersen
Senior Project Manager
Tlf: +45 2688 0228