The aims of this project were:

• To obtain practical experience from the establishment and operation of a low temperature heat storage system in a limestone aquifer, in connection with a district heating system; and
• To demonstrate the possibilities of commercial use of this type of aquifer in heating systems in combination with heat pumps.

The waste heat from a nuclear research reactor was used as a heat source for a 2.2 MW heat pump that was connected to a district heating system. The temperature of this waste heat was between 40°C and 45°C. However during normal operation, approximately three times as much waste heat was available as it could have been utilised by the heat pump. The nuclear reactor used to close down for 5 days every 4 weeks and during this period heat was being supplied by the combustion of oil. The idea was to store surplus heat from the reactor in a limestone aquifer and extract this heat during periods of reactor shutdown. Two main wells 100 metres apart were used, one for injection of the heated water, and the other one for extraction. The extracted water was expected to be at a temperature of around 30 °C. Two further wells were drilled for measurement purposes and equipped with temperature and pressure transducers that were connected to a computer system.