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Large Heat Pumps in Europe: Sea water heat pump for district heating in Norway

Thursday, January 18, 2018
Large Heat Pumps in Europe: Sea water heat pump for district heating in Norway
2018/01/17
Jan. 16, 2018
In 2012, Oslofjord Varme AS set a milestone with Europe’s first district heating project based on two UNITOP(R) 43/28 water/water heat pumps using the low Global Warming Potential (GWP) refrigerant HFO-1234ze, a HydroFluoroOlefin (HFO) with a GWP lower than 1 from Honeywell. The heat pump supplier was Friotherm AG, Switzerland.
 
The 340-hectare site of Fornebu is situated 10 kilometers from downtown Oslo with its strong commercial and financial community. The development plan for the area includes housing for a population of 11 000 and 15 000 work places on an area of 1 350 000 m2. The Fornebu development site is equipped with a district heating/cooling system which has a future estimated maximum heating power demand of 60 - 70 MW, and a heat production of 100 - 125 GWh/year. In the energy concept it has been decided that the main heat load will be covered with high capacity heat pumps and the peak load during the coldest period with bio-oil boilers. Further increase of heating and cooling demand of the Fornebu development site resulted in the construction of the Rolfsbukta heat pump plant, which is operating in the basement of a hotel since 2012.
 
As a response to the increasingly restrictive environmental regulations of refrigerants, the use of the new working fluid HFO-1234ze was decided. The classification society Norske Veritas was engaged by the Oslofjord Varme to perform a risk analysis for the heat pump plant using this new slightly flammable working fluid with a global warming potential below 1. The results showed that compared to the refrigerants from safety class A1 some additional safety precautions had to be taken. The emergency ventilation of the machinery room had to conform to ATEX 94/9/CE and an automatic power cut-off switch for the case of a refrigerant leakage was installed.
 
The total heating capacity of both heat pumps in Winter Mode is 16MW. The two heat pumps simultaneously produce chilled water at 2.5°C for district cooling, with heat recovery at 75°C for district heating. If the cooling demand is too low, the additionally required low temperature heat is extracted from sea water by the means of intermediate heat exchangers.

In Summer Mode the two compressors of each heat pump are working in parallel. With reduced isentropic lift and indirectly cooling by sea water as heat sink, both units are producing up to 20 000kW of cooling capacity with chilled water at 2.5°C. The Rolfsbukta plant is the first and largest heat pump plant worldwide, using HFO-1234ze and is an important development in the use of new ultra-low GWP working fluids.
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