Testing and Evaluation of New Refrigerants for Railway Vehicle Air Conditioning Systems

Due to the European "F-Gas" regulation, the climate technology experts at DB Systemtechnik are working together with air conditioning manufacturers to test alternative refrigerants for future use in railway vehicle air conditioning systems. On behalf of DB AG and in collaboration with air conditioning manufacturer Kiepe Electric, the natural refrigerant CO2 (R744) is being tested as part of the "HLK-Natur" testing project. The test units are two air conditioning systems with heat pump functionality inside a double-decker vehicle operated by DB Regio.

Since the thermodynamic process and pressure conditions of R744 differ significantly from conventional systems, DB AG is using not only test bench and operational trials but also simulations of the overall thermodynamic process to gather experience and insights into R744 and air conditioning systems with heat pump functionality.

In the context of the testing project, simulations were carried out using the software "Dymola," which helped identify thermal boundary and extreme ranges. Moreover, various scenarios were modeled and simulated with the software. These included the influence of ice formation on the ambient heat exchanger in heat pump mode, parameterization of design parameters, and different control strategies for the air conditioning system. With these calculations, it was possible to gain insights into the performance and controllability in boundary areas before the physical test units were created.

The overall model of the air conditioning system and the thermal model of the carbody were validated through test bench and climate chamber experiments. The test bench trials were conducted at Kiepe Electric’s partner, the Austrian Institute of Technology in Vienna. The vehicle tests were performed in DB Systemtechnik’s climate chamber in Minden. The use of the virtual twin allowed potential sources of error to be identified early and causes to be traced and eliminated.

As a result, air conditioning system operators will benefit from optimized and innovative air conditioning units with a higher maturity level, reduced maintenance effort, and therefore lower costs. In this project, the climate technology experts at DB Systemtechnik applied their extensive expertise in climate simulation and evaluation to the early assessment and optimization of industrial system concepts, providing value to the industry and business sectors.