Challenge
Premogovnik Velenje, Slovenia's only operating coal mine, is located at the centre of one of the country's most significant energy-transition regions. As the Šaleška Valley prepares for a lower-carbon future, the mine is developing new ways to make use of the energy resources already available within its operations.
One such resource is mine water. Pumped from approximately 500 metres underground at a temperature of around 20°C, it now provides the heat source for a new 1 MW high-temperature heat pump system.
Premogovnik Velenje idea and Resalta solution
Resalta, together with consortium partners Energoconsulting and Valmor, delivered a high-temperature heat pump system that uses underground mine water as its heat source.
Two high-temperature heat pumps with a combined thermal output of 1.0 MW were installed in a newly constructed plant room. Using mine water at around 20°C, the system can produce heating water at temperatures of up to 90°C, allowing the recovered energy to be integrated into the site's existing heating infrastructure.
A new 150 m³ reinforced-concrete mine-water storage tank provides a reserve for periods when water is not being pumped from the mine. A 12.5 m³ heating-water storage tank was also installed as part of the new system. The complete solution is integrated into the site's existing central control system.
Key project elements
- Two high-temperature heat pumps
- 1.0 MW combined thermal output
- Mine water at approximately 20°C used as the heat source
- Mine water pumped from approximately 500 metres underground
- Heating-water temperatures of up to 90°C
- Mine-water flow rates of up to 200 m³/h
- 150 m³ mine-water storage tank
- 12.5 m³ heating-water storage tank
- Integration into the existing central control system
Results
During summer, the heat pumps can cover the site's full heat demand for domestic hot water.
During winter, the system preheats the heating water used for mine-air heating, while the existing district heating system provides additional heat when required. The new high-temperature heat pump system is expected to reduce the site's demand for heat from district heating by up to 30%.
Construction began in November 2025, and the completed system was handed over to Premogovnik Velenje for use and operation in July 2026, within the contractual deadline.
Strategic relevance
The project demonstrates how energy already present within an industrial process can be recovered and transformed into a useful source of high-temperature heat.
Its potential also extends beyond the mine. In the future, the high-temperature heat pump system could be connected to the Šaleška Valley district heating network, providing an additional low-carbon source of heat for the wider area.
Project partners: Resalta d.o.o., Energoconsulting d.o.o., Valmor d.o.o.
Subcontractors: HTZ I.P. d.o.o., Spot gradnje d.o.o.
