14/9/2016

Heat pump to be connected to the Westman Islands' district heating

  • Vestmannaeyjar

District heating system was started up in the Westman Islands (Vestmanneyjar) in 1977. Initially, heat was extracted from the lava fields of the 1973 Heimaey eruption. Steam collection pipes were buried into the lava and steam lead to heat pumps heating the return water from the double piped district heating distribution system.

Eventually, as the lava fields cooled down, the steam did not produce enough heat for the district heating system. In 1988 an electrical heating boiler station was introduced to heat up the water using low priced unused electricity. In the boiler room were also oil heated boilers for when left over electricity was not available.

As electricity prices are expected to increase substantially, HS Veitur, the district heating owner and operator, has been looking for new ways to lower operation costs. In 2011 HS Veitur hired Verkis to prepare a feasibility study for a system where heat is extracted from the ocean using heat pumps to heat up the district heating return water. Several heat pump sizes and types were researched for the district heating system´s maximum power needs of about 15 MW. The conclusions showed that the most economical arrangement included a system where about 9 MW power was supplied from heat pumps and the remainder one third from electricity. However, since the economic gains of investing in the heat pump system is mainly dependent on electricity prices, the 2011 prices were so low that the profitability was considered insufficient at that time. Preparations were continued as electricity prices were expected to rise in the near future with subsequent improvement in the project´s profitability. In June 2015, Verkis completed a revision of the preliminary design report. Figure 1 below shows the expected internal rate of return for various electrical prices.

Figure 1. Internal rate of return from revised 2015 preliminary design report.  

Since the 2015 revised preliminary design report, HS Veitur has initiated multiple preparation phases, such as negotiating electricity prices and implementing subsidies on electrical heating etc. Verkis has also prepared tender documents and evaluated bids for heat pumps where a contractor, Varmalausnir ehf from Akureyri, was selected with a bid of 4 heat pumps totalling 10.4 MW. Bids were requested for drilling boreholes for seawater extraction and contracts are currently being negotiated. Building, pipeline and electrical design process is commencing. Anticipated start of operations is the winter 2017 - 2018.

Heat pump operates similarly to a refrigerator. The sea water is directed through the heat pump and cooled down and the energy extracted from the cooling process is used to heat up the return water from the district heating system. Figure 2 from the preliminary design report shows a simplified systems chart for the 9 MW heat pump. The figure shows flow and temperature numbers for two scenarios: maximum strain (15 MW) and average strain (8 MW). The heat pump cools down the sea water from about 7°C to 3°C heating up the 34°C return water from the district heating system. When power needs are below the heat pump´s 9 MW capacity, the return water is heated to 77°C which is the required temperature for the district heating system. When power needs exceed the heat pump capacity, the return water is directed to the boiler room where temperature is brought up to 77°C with electrical heating. 

Figure 2. Westman Islands district heating 9 MW heat pump, system arrangement

The system arrangement in Figure 2 assumes an efficiency factor of 3.0, i.e. one-third of the energy extracted from the heat pump is for the electricity driving the pump and two-thirds (around 6 MW) come from the ocean. The heat pump to be installed from Varmalausnir is 10.4 MW which is a bit larger than originally designed and with a higher efficiency factor of 3.55 so the energy extracted from the ocean is closer to about 7.5 MW.

Table below shows the expected district heating system electrical usage with and without heat pump system installed. 

  Without heat pump
GWh/year 
With heat pump
GWh/year 
Electrical use boiler 78,6 5,3
Electrical use heat pump 0 20,7
Electricity for sea extraction 0 1,2
Total 78,6 27,2

Main parts of the project include:

  • Sea water extraction and discharge of cooled sea water
  • Heat pump station including all equipment
  • Connecting heat pump station to boiler room station

Total capital cost for the heat pump station including all structures and equipment is estimated around 1,100 million icelandic kronas.

Verkís has also been involved in projects related to increasing reliability of the power supply to the Westmann islands including modification of the Rimakot substation and implementation of a new high-voltage submarine cable, more.