Large Heat Pumps for District Heating and Cooling
Large heat pumps are becoming a cornerstone in modern district heating and cooling systems. These systems offer an efficient and sustainable way to provide heating and cooling by harnessing renewable energy sources. In Denmark, initiatives to integrate large-scale heat pumps into district heating networks have demonstrated significant environmental and economic benefits.
Types of Heat Pumps and Their Applications
Large heat pumps can be categorized based on the type of source they use air, water, or ground. In Denmark, water-source heat pumps, particularly those using seawater, have been notably successful. For example, the Aalborg Forsyning project plans to utilize a 100-175 MW seawater heat pump to supply 25% of the district heating in Aalborg by 2025.
Similarly, HOFOR in Copenhagen is planning extensive investments in heat pumps, aiming to reduce reliance on biomass and fossil fuels while integrating green power from wind turbines.
Environmental Impact and Efficiency
Large heat pumps significantly reduce carbon emissions by using renewable energy sources. The transition from coal-fired power plants to heat pumps is a pivotal move towards achieving carbon neutrality. For instance, Esbjerg’s installation of seawater-based heat pumps with CO2 as the refrigerant marks a major step in reducing fossil fuel dependency. Read about the case in the city of Esbjerg here.
Heat pumps are also highly efficient, with seasonal coefficient of performance (SCOP) values around 3, meaning that two-thirds of the heat delivered comes from the source and one-third from electrical input. This efficiency can be further enhanced by integrating thermal energy storage systems, allowing heat to be stored and used when electricity prices are high, thus balancing the grid more effectively.
Economic Benefits
The shift to large heat pumps is driven not only by environmental goals but also by economic incentives. Heat pumps offer cost benefits over traditional gas and biomass systems due to their higher efficiency and lower operating costs. The flexibility in using electricity, particularly from renewable sources, during low-price periods further enhances their economic viability.
Technological Advancements
Technological advancements in heat pump systems, such as using CO2 as a refrigerant, have improved their performance and environmental impact. Denmark has seen a rapid adoption of CO2 heat pumps, with significant projects already in place and more planned for the future.
CO2 Heat Pumps
Since 2022, CO2 heat pumps have emerged as a new technology in Danish district heating systems. Selecting the appropriate heat pump for a specific application involves a complex decision-making process, primarily influenced by capital expenditure (CAPEX), operational expenditure (OPEX), and return on investment (ROI).
The key technical considerations are:
- Functionality: Performance and reliability.
- Performance in varied conditions: The defrost function in winter is especially critical.
- Flexibility: Quick start/stop capabilities and the ability to supply high-flow temperatures.
- Robustness: Ability to handle fluctuating district heating water temperatures.
- Efficiency: Coefficient of performance (COP).
Flexibility is particularly relevant for networks with additional heat-producing units, such as gas motors (CHP), biomass boilers, and large energy storage tanks. Unlike conventional heat pump systems used for both space heating and domestic hot water (DHW) heating, CO2 heat pumps achieve their highest coefficient of performance (COP) in combined heating and DHW heating modes. The lowest COP is observed in space heating mode.
Natural refrigerants, including ammonia, carbon dioxide, and various hydrocarbons, have gained significant attention as sustainable alternatives to synthetic refrigerants. The phasing out of Freon (CFCs) in the 1980s due to its ozone-depleting properties led to the adoption of hydrofluorocarbons (HFCs), which, while not damaging to the ozone layer, have extremely high Global Warming Potential (GWP) values, sometimes exceeding 20,000 times that of CO₂.
In recent years, the focus has shifted to “Low GWP” refrigerants. However, these alternatives, such as hydrofluoroolefins (HFOs), degrade into PFAS (per- and polyfluoroalkyl substances), which are persistent environmental pollutants. Studies suggest that up to 60% of all PFAS in the environment may originate from refrigerants.
In Denmark, the heating industry largely avoids these synthetic refrigerants, favoring natural refrigerants like ammonia (NH₃), CO₂, and hydrocarbons. These natural options have much lower GWP values and are often more efficient. Danish companies primarily use these natural refrigerants in heat pumps, positioning Denmark as a leader in this environmentally friendly technology.
For more information on the transition to natural refrigerants and their benefits, you can refer to the detailed reports on sustainable refrigeration technologies provided by various sources, including industry publications and environmental research (IIAR Safe Refrigerants) (Quality Digest).
Air to Water Heat Pump Overview
Economic and Technical Data for an Air/Water Heat Pump
*) Based on experience from completed projects and excludes project proposals, authority processing, and grid connection.
| Description | Value | Unit |
|---|---|---|
| Cold start time | 0.5-1 | hours |
| Warm start time | 6-10 | minutes |
| Acceleration in operation | 30-60 | seconds |
| Known capacity range | 1-15 | MW |
| Regulation capability | 10% | per minute |
| Minimum load of full capacity | 25% | |
| Investment cost | 5-8 | Mio kr./MW |
| Fuel type | Electricity | |
| Annual efficiency | 260-330 (depending on heat source) | % |
| Heat source | Air, waste heat, flue gas, waste, groundwater, and seawater | |
| Variable costs | 10-20 | kr./MWh |
| Fixed costs | 15-20,000 | kr./MWh |
| Expected construction period | Existing building: 12-18 New construction: 12-24 |
months |
| Area requirement including heat exchangers, pipes, pumps, etc. | < 1 MW: ~100 3-10 MW: ~50 > 10 MW: ~30 |
m²/MWh |
| Lifetime | 20-25 | years |
| Functionality | Peak load, spot market, regulating power, accumulation |
Source: Drejebog | Fossilfri spidslast i fjernvarmesystemet, Energistyrelsen (in Danish)
Seawater Heat Pump Overview
Economic and Technical Data for a Seawater Heat Pump
*) Based on experience from completed projects and excludes project proposals, authority processing, and grid connection.
| Description | Value | Unit |
|---|---|---|
| Cold start time | 0.5-1 | hours |
| Warm start time | 6-10 | minutes |
| Acceleration in operation | 30-60 | sec. |
| Known capacity range | 20-50 | MW |
| Regulation | 10% | per minute |
| Minimum load of full capacity | 25% | |
| Investment cost | 4 | Mio kr./MW |
| Fuel type | Electricity | |
| Annual efficiency | 370 (depending on heat source) | % |
| Heat source | Air, waste heat, flue gas, waste, groundwater, and seawater | |
| Variable costs | 10 | Kr./MWh |
| Fixed costs | 30,000 | Kr./MWh |
| Expected construction period | 12-24 | months |
| Area requirement including heat exchangers, pipes, pumps, etc. | 30 | m²/MWh |
| Lifetime | 20-25 | years |
| Functionality | Peak load, spot market, regulating power, accumulation |
Source: Drejebog | Fossilfri spidslast i fjernvarmesystemet, Energistyrelsen (in Danish)
Future Plans
In Denmark, heat pump technologies have matured, and they work. A vast amount of experience has been gathered from all the projects, both good and bad, and the industry generally knows where to focus. The current emphasis is more on flexibility and robustness, followed by efficiency.
Looking ahead, Denmark plans to continue expanding its heat pump infrastructure. For example, Copenhagen’s strategy includes installing up to ten large heat pumps by 2033, contributing to the city’s goal of becoming climate-positive by 2035. Read the article “District heating in Greater Copenhagen 2050” to get further insight.
Conclusion
Large heat pumps revolutionize district heating and cooling systems by providing a sustainable, efficient, and economically viable solution. As more cities and countries adopt this technology, the global shift towards renewable energy and carbon neutrality becomes increasingly attainable. The projects in Denmark serve as a model for integrating large-scale heat pumps into district heating networks, showcasing their potential to transform urban energy systems.
Energy storage is critical to a successful electrification strategy for district heating networks with alternative heat sources and variable electricity costs. Efficient and flexible energy storage solutions significantly enhance the business case for adopting CO2 heat pumps and other renewable technologies. Read more about energy storage solutions.
Mega Heat Pumps
Morten Jordt Duedahl has invited Raymond Decorvet from MAN Energy Solutions and Claus A. Nielsen from Esbjerg DH company, DIN Forsyning, to discuss large heat pumps and how to include them in the heat portfolio for a large DH company in Denmark.