Expansion Hellisheidi geothermal plant

Expansion of the heating plant at the Hellisheidi geothermal heat and power plant, which produces hot water for domestic heating in the capital area, has been completed. Mannvit was responsible for the project’s overall design, Project Management, tendering of construction contracts and materials, HAZOP analysis and start-up tests and commissioning.

The expansion was originally planned to take place in 2023, however, due to increase in the use of hot water in the capital area beyond forecasts, Reykjavik Energy’s ON decided to complete the project in 2020. Increased demand in the capital area of Reykjavik placed increased pressure on Veitur's (District heating company) geothermal water wells, located in Reykjavík and Mosfellsbaer, especially during peak hours and on cold days.

With the increased production capacity of hot water in the geothermal power plants, there is an opportunity to relieve the load on geothermal boreholes placed in Reykjavík and replace it with water from the Hellisheidi geothermal power plant, 24 km outside of Reykjavik.


Hitaveita Hellisheiðarvirkjun stækkun - Hellisheidi geothermal heating plant

For the cold-water supply, three 500 kW submersible pumps were added along with associated power transformers and 11 kV switchgear. The pumps are at a depth of 120 m and each pump has a capacity of 160 l/s. DN 1000 ductile was lengthened about 120 meters. Wellhead cellars were redesigned to improve access to equipment. Several changes were made to the drainage pipes to meet water protection requirements. The plant’s building did not need to be expanded, since the expansion was already planned during the building of the first phase.

In a heat station, two shell and tube heat exchangers connected in series were added to heat the water from 46°C to 83-93°C as needed. The water is heated with 117°C separated water (geothermal brine) which can be mixed with full-temperature separation water so that the temperature will increase up to 130°C. The total heat exchange area of ​​the expansion is 1650 m2. The heat exchangers are made of stainless steel and the pipes are super duplex 254 SMO. DN100 ductile pipes for ground water were lengthened and connected to the pumps.

Pump capacity for production water was increased by 20% with a 90 kW centrifugal pump. In the first phase, this expansion was planned, so there was no need to expand the power plant building. The capacity of the heating plant is now 200 MWth + 303 MWe in power production.

Services included: 

Geothermal dstrict heating engineering

Geothermal power plant engineering

Project Management 



  • Overall design
  • Project Management
  • Tendering of construction contracts and materials
  • HAZOP analysis
  • Start-up tests and commissioning
200 MWth 
Thermal heating cap.
3x500 kW 
Cold water pumps
Separator fluid temp

Hellisheidi geothermal power plant is Europe's largest geothermal plant. In addition, the plant owner and operator owns Jarðhitagarður (Geothermal Park). The Geothermal Park encompasses a wide range of operations, which aim to utilize the resources of Hellisheidi Power Plant in the best way possible, benefit the environment and create value. The resources available are electricity, cold water, hot water, steam and carbon dioxide.

ON Power


Hellisheidi Geothermal Power Plant