According to German train operator Deutsche Bahn, natural refrigerants – such as CO2 (R744) and propane (R290) – are the future-proof option for transport HVAC systems, with no bans on the horizon.
“The way to natural refrigerants is paved,” said Peter Danzer, Project Leader at Deutsche Bahn. “F-gases are a dead end; [they] are not the future. The industry must now follow the proven results of propane and CO2.”
Danzer shared details of Deutsche Bahn’s HVAC strategy – which has been partially driven by f-gas bans – during his presentation in the End User Panel session at the ATMOsphere (ATMO) Europe Summit 2023. The conference took place September 19–20 in Brussels and was organized by ATMOsphere, publisher of R744.com.
Having made a commitment to only use natural refrigerant-based HVAC systems in its new vehicles from 2020, the train operator already has a passenger train using propane-based air-conditioning units (alongside “state-of-the-art” electric heaters) and has been testing CO2 heat pumps for both heating and cooling, he said.
Deutsche Bahn plans to use both CO2 and propane in the near future and is “generally open” to both technologies, said Danzer. “CO2 is a refrigerant we can see in our trains in regular service,” he said. On the other hand, “it seems that propane can be operated without loss of cooling capacity under very high ambient temperatures [45°C/113°F], where with CO2 actually a small reduction of cooling capacity is to be considered.”
“The way to natural refrigerants is paved. F-gases are a dead end; [they] are not the future. The industry must now follow the proven results of propane and CO2.”Peter Danzer, Deutsche Bahn.
A call to industry
As of 2018, it was not widely understood within the transport sector that synthetic refrigerants were not a sustainable option, and there were very few efforts to move towards natural alternatives, explained Danzer.
But Deutsche Bahn had previous experience with natural refrigerants, having introduced AirCycle AC units in 2000. Across its fleet, a total of around 500 air-based units are in operation.
While the AirCycle AC units have been very energy efficient in normal operating conditions, there have been a number of issues that limited their adoption, including the amount of power required to run the units in high ambient temperatures. The units are also much bigger and heavier than comparable options, and there have been difficulties in sourcing rail carriages with air-based AC systems, explained Danzer.
To stimulate the development and adoption of other natural refrigerant-based systems, Deutsche Bahn invited suppliers to conduct trials.
From this call to industry came two trials, one led by rail equipment manufacturer Faiveley Transport (Wabtec) using propane-based AC units and the second a CO2 heat pump system for double-decker rail coaches from Kiepe Electric, a German manufacturer of transport equipment that is now part of Knorr-Bremse.
Having been tested from 2020–2021, the Faiveley’s R290 units have now been in regular operation from 2023. Testing for Kiepe’s CO2 heat pump concluded in September 2022.
The trials show that the energy consumption of R290 and R744 are comparable to synthetic refrigerants for cooling; however, in heat pump mode, natural refrigerants are much more efficient.
According to Danzer, the volume and weight of the propane and CO2 units are similar to that of Deutsche Bahn’s existing R134a-based systems, meaning that the new units could be integrated into rail vehicles without major adaptation.
He noted that train operators in a number of countries, including Austria, Italy, the Netherland, Norway and Switzerland, are introducing natural refrigerant-based HVAC systems as well.
“They all see that they have to change and that f-gases are not the future,” he added.
The cost of transitioning
“It is clear to everyone in the railway sector that synthetic refrigerants are not suitable in the long-term; however, the cost of replacing a train’s HVAC system is high,” explained Danzer during his presentation.
Typically, a train carriage’s HVAC unit is not replaced during the vehicle’s 30 years of operation, with systems designed to last their entire lifetime. But as the EU phases out the use of synthetic refrigerants under its F-gas Regulation, train operators like Deutsche Bahn are having to weigh their options: do they buy new vehicles or try to replace their HVAC units?
According to Danzer, replacing existing HVAC systems will cost European rail operators billions of euros.
“It is clear to everyone in the railway sector that synthetic refrigerants are not suitable in the long-term; however, the cost of replacing a train’s HVAC system is high.”Peter Danzer, Deutsche Bahn