Bitzer reports that its new CO2 (R744) compressors are more efficient and effective thanks to an increased volumetric flow rate, enabling them to better serve district heating applications.

“With a volumetric flow rate like 69.4 m3/h (2,450.8ft3/h) for our 8FTE series and 82 m3/h (2,895.8 ft3/h) for the 8DTE series, our compressors are engineered to meet diverse heating demands,” said Tobias Fuhrer, Product Manager of Reciprocating Compressors at Bitzer.

“These numbers aren’t just figures,” he added. “They represent Bitzer’s commitment to providing solutions for everything from commercial complexes to industrial use.”

Fuhrer noted that the German company’s “robust, efficient and versatile” 8-cylinder compressors are particularly suitable for “a wide range of district heating applications.”

He specifically called out BITZER’s 8CTE compressor series, which has a 99.2m3/h (3,503.2ft3/h) flow rate.

“Our goal is to ensure that every compressor we design meets the expectations of a modern heating system,” said Fuhrer. “This approach is significant in an era where efficiency and sustainability are not just preferences but necessities.”

Fuhrer’s remarks were presented at the European Heat Pump Summit, which took place in Nuremberg, Germany, October 24–25. His presentation was titled “Large Scale Heat Pumps with District Heating with R744.”

During the presentation, Fuhrer emphasized how district heating systems have consistently featured core components like heat sources, heat pumps, electrical energy sources and heat storage tanks. He also noted the shift toward incorporating renewable energy sources, such as wind and solar power, which aid in decarbonizing the heating process.

He highlighted the various generations of district heating systems, from the first steam-based system to more recent approaches, which use water/brine solutions. “The water/brine-based CO2 heat pump solutions are mostly popular in Scandinavian countries, where they operate with lower supply and backflow temperatures, achieving [a] high COP,” said Fuhrer.

CO2 as a refrigerant

CO2 is a strong option for district heating systems and offers a myriad of advantages over competing refrigerants, which Fuhrer touched on during his talk.

“CO2 is non-flammable and non-toxic, making it a safer alternative in heating applications, but the benefits extend far beyond safety,” he said.

“Its volumetric refrigeration capacity helps to operate it with much less and smaller compressors and narrow pipes, reducing the system’s physical footprint,” he noted.

The properties of CO2 make it ideal for supercritical operation, enhancing the efficiency of district heating systems. “When CO2 is used in a supercritical state, it aligns well with heat absorption and release processes,” Fuhrer explained. “This means we can extract more heat per unit of CO2 compared to traditional refrigerants like R134a.”

Fuhrer stated that CO2’s behavior in supercritical phases allows for a more uniform temperature glide, closely matching the needs of water heating systems.

CO2 vs. R134a

Fuhrer’s remarks included a comparison between CO2 and R134a systems, with those using the natural refrigerant proving to be much more efficient.

“In a basic cycle, the COP of a [transcritical CO2 booster] system was 2.8, whereas, for the R134a systems, it’s approximately 2.3 under the same operating conditions,” said Fuhrer. “This difference is significant for large-scale heating applications.”

Fuhrer didn’t just highlight the superior performance of CO2 but also delved into how its COP can be further improved.

“When we integrate techniques like parallel compression in CO2 systems, the COP can be increased to about 3.2,” he said. “Further efficiency of CO2 systems can be increased by implementing an ejector in the CO2 parallel compression booster system. These advancements show that the potential of CO2 in district heating systems exceeds what traditional refrigerants like R134a can offer.”

Fuhrer cited Fenagy’s district heating network installed in Jutland, Denmark, as an example. The project has air-to-water heat pumps, which have a COP of 3.2 and use CO2 as a refrigerant. Another example is the Frederiksberg district heating network, which supplies heat to approximately 800 households with a COP of 3.2 at 6°C (42.8°F) ambient conditions, using CO2 as the refrigerant.

“These advancements show that the potential of CO2 in district heating systems exceeds what traditional refrigerants like R134a can offer.”

Tobias Fuhrer, Product Manager of Reciprocating Compressors at Bitzer

Author Saroj Thapa