Aalborg faced the dual challenge of reducing its reliance on fossil fuels for district heating and meeting ambitious climate goals without increasing energy costs for residents. Traditional heating methods contributed significantly to carbon emissions and operational expenses. Additionally, the city needed a solution that could integrate seamlessly with its existing infrastructure while utilizing local resources more effectively. The challenge was to find a sustainable, scalable, and economically viable alternative that could deliver consistent heating performance year-round.

To address these challenges, Aalborg Forsyning installed two 3 MW CO₂ heat pumps at its city’s primary wastewater treatment facility. These pumps extract thermal energy from treated wastewater, which ranges in temperature from 7°C to 25°C, and deliver up to 6 MW of heating to the district network. The system uses high-efficiency compressors, plate heat exchangers, and smart controls that dynamically adjust to input and return temperatures. With a supply temperature of up to 75°C and full compatibility with existing infrastructure, the solution exemplifies circular energy use—transforming waste heat into a valuable community resource.

The installation now provides sustainable heating to over 1,300 households, significantly reducing carbon emissions and operational costs. With a coefficient of performance (COP) of 3, the system is three times more efficient than conventional heating methods. The use of CO₂ (R744), a natural refrigerant with a global warming potential (GWP) of just 1, ensures compliance with F-gas regulations and supports long-term climate goals. The project has created value for residents, the municipality, and the environment by showcasing how local resources can be harnessed for large-scale, sustainable energy solutions.