Reuse of Wastewater Provides Heating for District Heating
SUSTAINABLE DISTRICT HEATING FOR 1,300 HOUSEHOLDS
To provide sustainable district heating, Aalborg Forsyning has installed a large-scale CO₂ heat pump at Renseanlæg Øst, the city’s main wastewater treatment plant. This system now delivers clean, renewable heating to over 1,300 households using the energy embedded in treated wastewater.
The installation features two 3 MW CO₂ heat pumps, delivering 6 MW of heating to the district heating network. With a COP of 3, it is a highly efficient and environmentally friendly alternative to fossil-based heating.
FACTS
End-user: Aalborg Forsyning
Contractor: Aktive Energi Anlæg
Segment: District heating
Background: Reuse wastewater for the district heating
Products: 2 x SteelXL 5+5x0
Specifications:
- 6 MW heating capacity
- Permanent Magnet Motors for maximum energy savings
- Parallel Compressors for maximum energy savings
- High Pressure Ejectors for maximum energy savings
Fully compatible with existing infrastructure
The system can deliver up to 75 °C supply temperature, with a return temperature of 40–45 °C. This makes it fully compatible with Aalborg’s existing district heating infrastructure. Wastewater temperatures vary between 7 °C and 25 °C, with a design basis of 8 °C — conditions in which the Advansor CO₂ heat pumps operate with high and stable performance.
Each 3 MW heat pump is equipped with high-efficiency CO₂ compressors, plate heat exchangers, and a smart control system that dynamically adjusts the cycle based on input water temperatures and district heating return temperatures. CO₂ (R744) is a natural refrigerant with a GWP of 1, complying with recent F-gas regulations.
A clear path towards decarbonization
This project demonstrates that heat pumps using wastewater are not just reliable — they are an economically and environmentally superior alternative to fossil fuel-based heating. Aalborg Forsyning’s system is a textbook example of circular energy use, where waste heat from a municipal process is transformed into a community resource. It significantly reduces both operating costs and carbon emissions, with a remarkably short payback time and a long service life.
As cities across Europe strive to meet ambitious climate goals while keeping energy bills in check, solutions like this show what’s possible when clever engineering meets local ambitions. Aalborg’s investment proves that reusing wastewater heat isn’t just green — it’s financially and technically sound.