The case

In collaboration with Finnish contractor Caverion, Fenagy has supplied six isobutane/propane heat pumps to a utility company providing district heating to Kajaani in north-east Finland (Phase 1, 2025). The heat pumps recover excess heat from a nearby data centre and feed it into the district heating network. Following the success of this first phase, a second phase has been agreed (2026) for an additional nine units – bringing the total to 15 heat pumps.

The data centre is being expanded in stages, and Fenagy’s modular heat pump concept matches this approach precisely: capacity is added as the facility grows, ensuring the system is always right-sized to the actual cooling demand and the waste heat it generates. By connecting heat pumps to the existing cooling water circuit, the system both provides server room cooling and recovers excess heat for district heating. The original chillers remain in place for backup only.

As data centres require cooling year-round, they are a stable and reliable heat source for heat pumps. In winter, waste heat is recovered for heating the city - in summer, excess heat is released via the existing dry coolers.

The heat pumps

The heat pumps are customised HCI-3000 units designed to provide both heating and cooling. Each unit has three compressors - two using isobutane and one using propane.

Waste heat from the data centre enters at around 30°C and is raised to approximately 85°C to meet district heating requirements. On the cold side, the units supply 20°C water for server room cooling, independent of the district heating return temperature, which in this case is about 50°C.

Isobutane and propane are both highly efficient, PFAS-free, natural refrigerants with an extremely low global warming potential.

When fully implemented across both phases, the system will deliver 33.5 MW of heating and 25.8 MW of cooling..

Read more about this project in a Deep Dive article published by ATMOshere.