Heat pumps using waste water in Gothenburg, Sweden
Four heat pumps at Rya Värmepumpverk in Gothenburg, Sweden, extracts heat from a waste water treatment plant. The excess heat is delivered to the local district heating network.
A great amount of the heating produced in the district heating system of Gothenburg is from excess heat. However, during winter, it is necessary to operate other production facilities such as biomass and natural gas boilers and CHP units. To contribute with environmentally friendly heating, the city of Gothenburg established Rya Värmepumpverk, a local heat pump facility with four heat pump units. The heat pump plant was established in 1985 with multiple heat pump units. The units extract heat from the local waste water treatment plant. The total heating capacity for the heat pumps is 160 MW, divided upon two 30 MW heat pumps and two 50 MW heat pumps. All heat pumps are compressor driven and supplied with electricity from the Swedish grid.
As the heat pumps are greatly flexible they operate as peak-loads. The heat pumps accordingly act as support for the baseload in Gothernburg consisting of waste incineration and waste heat recovery from a local refinery. The waste water has temperatures of approximately 12°C, which is cooled to approximately 3°C through the heat pump. The heating delivered to the district heating network is between 75 and 85°C, depending on season and district heating water is returned at 45°C.
All four heat pumps contain approximately 100 ton of the refrigerant R134a. The greatest environmental effects from the heat pumps are accordingly potential leakages of this, as 1 ton of R134a corresponds to 1430 CO2 equivalents. However, such leakages are uncommon. In 2013, the four heat pumps had a 11,496 operation hours, producing a total of 443.0 GWh of heating. All heat pumps operate with a COP just above 3.0
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