Fenagy Large-scale Heat Pump

State of the Art

Many lessons have been learned from the application of CO₂ heat pumps in large-scale district heating schemes. The Danish District Heating sector has continually been evolving, paving the way for the integration of efficient electrically driven heat pumps. Typically, 70°C flow and 40°C return temperatures are used. However, depending on the season and system characteristics, temperatures vary between 60 to 80°C flow and 30 to 50°C return.

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Large-scale Heat Pump
District Heating Installation

If the temperature difference between the source and flow temperature is small, then heat pumps, in general, consume less power. If the temperature difference is large, the heat pumps consume more power. Typically, a seasonal efficiency (SCOP) will be around 3. That means 2/3 of the heat delivered to the system comes from the source and 1/3 from the electrical input.

Due to the nature of a CO₂ heat pump cycle, CO₂ heat pumps behave differently. For example, the COP (Coefficient of Performance) factor drops only 0.1 when increasing the flow temperature from 70°C to 80°C. For heat pumps with other refrigerants COP factor drops 0.3 to 0.6. This ability to deliver high-grade heat helps optimise thermal storage because more energy can be stored. 

Heat pump product range

In this table you will see all the relevant key data for the heat pump product range:

Key StatisticsCO2-6xxCO2-12xxCO2-18xx
TypeRack CO2 Heat Pump – Air to Water / Water to Water Models Available
Capacity (kW)From about 600 kW to 1800 kW heating capacity, depending on operating conditions.
Dimensions (m)2.5/4.8/1.32.5/8.0/1.32.5/10.0/1.3


CO₂ heat pumps play a crucial role in reducing the carbon footprint of district heat networks. By using a natural refrigerant, they avoid negative environmental impacts and further support decarbonization efforts.

High-grade Heat

CO₂ as a refrigerant can achieve high-grade heat without affecting the efficiency of the heat pump. With a flow temperature of up to 85 degrees, CO₂ heat pumps are ideal for a variety of applications and for optimizing thermal storage use.

Energy Efficiency

CO₂ heat pumps require low return temperatures, ideally below 45˚ C to achieve a large delta T, which leads to an energy-efficient heat network. By reducing network pumping costs and distribution losses, they help lower energy bills and increase the efficiency of the energy centre heat generation.

Natural Refrigerant:

Unlike synthetic refrigerants such as CFCs, HCFCs, HFCs, and HFOs CO₂ is a natural refrigerant that has a global warming potential of 0 and does not cause any harmful impacts. It is an ideal alternative to synthetic refrigerants that are being phased out or planned for phase-down.

Efficient Heat Networks

CO₂ heat pumps are more COP-sensitive to the return temperature than the alternatives. However, this should not be perceived as a problem, as a low return temperature indicates an efficient operation of the heat network. Schemes that have high return water temperature aim to improve their efficiency. They optimize heat use at terminal units and lower the return water temperature.

Therefore, CO₂ heat pumps that operate with low return temperatures are a perfect fit for efficient networks.

Heat Pump documents

Please find relevant links for further reading below, or visit our downloads page.

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