In a three-year research study testing the viability of German manufacturer Liebherr’s CO2 (R744) air-conditioning system on a long-distance passenger train, the “eco2jet” project showed an energy efficiency improvement of 30%.

The study concluded that this system is a “reliable and technologically mature concept.”

The aim of the project was to develop an environmentally friendly CO2 air-conditioning system for rail vehicles as an alternative to HVAC systems operated with conventional refrigerants, according to a recent statement by Liebherr.

To this end, a near-production “Fast Track Demonstrator” (FTD) for an HVAC system with heat pump functionality using CO2 was developed and installed in a passenger coach from the Railjet fleet operated by the Austrian Federal Railways (ÖBB) – also a project partner.

The primary objective of the project was to meet the comfort criteria of the passengers in a wide operating range with low environmental impact by using novel heat exchangers, an advanced system architecture and an intelligent control strategy in the future.

Compared to conventional air-conditioning systems, “an increase in energy efficiency by at least 30% in real rail transport is achieved” with the eco2jet HVAC system with a heat pump function, according to research findings.

Liebherr had previously tested the FTD in a climatic chamber and then, in cooperation with ÖBB, recorded and evaluated the performance of the system in regular train operation under real conditions. “In the more than three-year eco2jet demonstration phase from May 2018 to August 2021, the air-conditioning system with CO2 as refrigerant proved to be a reliable and technologically mature concept,” said Liebherr. “The environmentally friendly, energy-saving regular operation of an ÖBB long-distance passenger train with this pioneering technology on board is thus guaranteed.”

The project was funded by the Austrian Climate Energy Fund and supported by the Austrian Research Promotion Agency (FFG) in Vienna.

Additional to Liebherr and ÖBB, the eco2jet consortium included Austrian partners such as Advanced Thermal Technologies (ATT), the Institute for Advanced Energy Systems & Transport Applications (IESTA), Obrist Engineering, Rupert Fertinger, TU-Graz and the Virtual Vehicle Competence Center.

“The environmentally friendly, energy-saving regular operation of an ÖBB long-distance passenger train with this pioneering technology on board is thus guaranteed.”


Wider use possible beyond rail

The use of the refrigerant R744 in air-conditioning represents an “innovative, future-oriented technology” for applications in the railway sector,” according to the research findings. Systems and components can be used not only for long-distance trains but also for local trains, trams, or subways. Subsequently, non-rail vehicles such as trucks, cars and airplanes will also benefit from the eco2jet solution, the researchers said.

CO2 air-conditioning in trains is not a novel concept. Liebherr previously worked with the Deutsche Bahn, Germany’s main railway company, to test and install natural-refrigerant-based air-conditioning in its rail vehicles. The aim was to exclusively use natural refrigerants in its new trains from 2020 onwards.

In 2019, China-based engineering firm CRRC Dalian Locomotive Research Institute developed one of the world’s first CO2-based air-conditioning systems for railway transport.

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