Decarbonizing Industry and District Heating: Fraunhofer ISE Unveils Breakthroughs in High-Temperature Heat Pump Technology

The transition to a climate-neutral industrial sector and the modernization of urban heating networks represent two of the most significant engineering challenges of the 21st century. As Europe moves to decouple industrial output from fossil fuel dependency, the role of high-temperature heat pumps (HTHPs) has shifted from a peripheral technology to a cornerstone of the energy transition.

On October 7, 2026, the Fraunhofer Institute for Solar Energy Systems (ISE) released findings from its latest research initiatives—the "FernWP" project and the "Reallabor GroßWP" (Large-Scale Heat Pump Real-World Lab). These studies provide critical insights into how heat pumps can reliably deliver process steam at temperatures up to 160°C and how large-scale heat pump systems can be integrated into complex municipal district heating networks.

Main Facts: The New Frontier of Thermal Energy

The core finding from the Fraunhofer ISE research is that high-temperature heat pumps are no longer merely theoretical solutions; they are viable industrial assets. However, their success is strictly contingent upon a "systemic design approach."

According to the report, simply scaling up components from standard refrigeration or building-service engineering is insufficient for the rigors of heavy industry. Instead, successful implementation requires a holistic integration of heat sources, refrigerants, heat exchangers, hydraulic configurations, and sophisticated control strategies.

The research highlights two distinct but complementary research paths:

1. The FernWP Project: A laboratory-based initiative focused on the thermodynamics of process steam and pressurized hot water up to 160°C.
2. The Reallabor GroßWP: A long-term monitoring study of five large-scale heat pump plants currently operating within German district heating grids, providing data on real-world reliability and efficiency.

Chronology of Research and Development

The path toward these current findings has been a multi-year effort to bridge the gap between small-scale lab tests and industrial-grade utility.

• 2023: Launch of the "Reallabor GroßWP" monitoring program. Researchers began capturing live performance data from five large-scale heat pump installations across Germany to understand how these units interact with existing power plant infrastructure.
• Early 2024: Development of the advanced laboratory test stand within the FernWP project. The primary goal was to simulate the replacement of coal-fired boilers with heat pump technology.
• October 2026: Official reporting of findings. The Fraunhofer ISE synthesizes years of operational data, confirming that when properly integrated, these systems meet their design specifications, even under the volatile conditions of modern power markets.
• Future Roadmap (2027 and beyond): The FernWP project is scheduled to run until September 2027. Future work will focus on modeling the interfaces of heat pumps in power plant clusters to enable predictive, economically optimized operation.

Supporting Data: The Complexities of Real-World Operation

While laboratory results show the technical potential of reaching 160°C, the "Reallabor GroßWP" data reveals the complexities of the field.

The Impact of Source Temperature

A critical observation involves the use of river water as a heat source. Researchers identified that when source water temperatures drop below approximately 6°C, the thermal output of the heat pumps begins to decline. While this is not a universal limit for all heat pump technology, it serves as a vital design constraint for engineers. It dictates that the thermal capacity of the source must be rigorously analyzed during the planning phase to avoid mid-winter capacity gaps.

Shift in Operational Profiles

The study also highlights a fundamental shift in how heat pumps are deployed. Early planning often assumed a seasonal, base-load operation. However, current data shows that operators are increasingly utilizing heat pumps according to daily demand profiles and electricity market price fluctuations. This shift imposes higher demands on the equipment, specifically regarding:

• Frequent Start-Stop Cycles: Higher mechanical stress on compressors and valves.
• Standby Durability: Maintaining availability during periods of low market demand.
• Service Intervals: The need for predictive maintenance to ensure high system availability despite dynamic operation.

Official Responses and Expert Perspective

The researchers at Fraunhofer ISE emphasize that the "heat pump" is not a standalone solution; it is a component of a larger symphony of infrastructure.

Dr. Ursula Wittstadt, Senior Engineer and Project Lead of FernWP, explains the necessity of flexibility:

"For industrial applications, reaching the maximum temperature is not the only metric for success. A high-temperature heat pump must also provide process steam or pressurized hot water efficiently and reliably under changing heat sources, varying loads, and diverse operational modes."

Axel Oliva, Project Lead for the Reallabor GroßWP, echoes this sentiment regarding the integration of heat pumps into the broader grid:

"Decisive for efficiency and availability is not just the heat pump itself, but the heat source, the hydraulic integration, the existing generation system, and the specific operational strategy. Operating within a power plant cluster requires deep knowledge of the existing infrastructure and the specific needs of the customer network."

These statements underscore a paradigm shift in the industry: moving from "plug-and-play" equipment to "systemic design."

Implications: The Road to Defossilization

The implications for the German energy market—and by extension, the European industrial landscape—are profound. Approximately 16% of German households rely on district heating. Transitioning these massive networks from coal or gas to electricity-based heat pumps is the most significant lever for reducing carbon emissions in the heating sector.

Economic and Technical Optimization

The data collected by the Fraunhofer ISE is currently being processed to create new methods for modeling and economic optimization. For manufacturers, the findings provide a roadmap for designing components that can handle high-pressure differentials and the use of flammable refrigerants like butane, which are being explored for their thermodynamic benefits in high-temperature cycles.

Safety and Regulatory Challenges

Because high-temperature operation requires specific refrigerants (like butane), safety remains a primary concern. The research projects are not only testing efficiency but also defining the safety protocols required for industrial-scale installation. Future research will focus on advancing these safety concepts, ensuring that as we scale up the technology, the risk profile remains manageable.

A Call for Integrated Planning

For industrial facility managers and municipal utility planners, the key takeaway is the necessity of "early-stage systemic integration." The Fraunhofer ISE findings suggest that retrofitting is rarely as simple as replacing a boiler with a heat pump. Instead, the entire hydraulic system must be re-evaluated to ensure the heat pump can operate within its "sweet spot" of efficiency.

Conclusion

The findings from Fraunhofer ISE represent a significant milestone in the maturity of high-temperature heat pump technology. By moving beyond the laboratory and into the complex, dynamic reality of German industrial and utility grids, researchers are providing the empirical evidence needed to de-risk the transition away from fossil fuels.

As the industry looks toward the 2026 Chillventa exhibition in Nuremberg, where these technologies will be showcased, the message is clear: the technical hurdles are being cleared. The next phase of the energy transition will be defined by the skill with which these systems are integrated, managed, and optimized within the broader, electrified energy economy. Through continued research, data-driven modeling, and a rigorous focus on systemic design, the vision of a carbon-neutral industrial process is becoming an engineering reality.

For those interested in the ongoing developments, the Fraunhofer ISE continues to provide technical updates and research outcomes via their official channels, with further findings expected as the FernWP project approaches its 2027 completion date.