Energy efficient and environmental neutral Heating, Ventilation and Air-Conditioning pilot unit for train applications.

R744trainHVAC Energy efficient and environmentally neutral Heating, Ventilation and Air-Conditioning pilot unit for train applications. The Norwegian Railway equipment of NSB is under continuous renewing, and the number of Rolling Stocks with HVAC (heating, ventilation and Air Conditioning) systems is increasing. In 2013, the total energy consumption of NSB related to public transport was 307 GWh el and 8.7 mill. litres of diesel. Currently available HVAC units for trains are commonly using either HFC-134a (75%) or HFC-407C (25%) as working fluids, which have a significant global warming potential when released into the environment. These units typically rely on inefficient direct electrical heating to cover heating demands. However, some system suppliers can offer HFC-134a HVAC systems with heat pump capabilities able to supply heating to the coach at ambient temperatures above -5 °C. HFC-134a is a synthetic fluid with a strong global warming potential (GWP) of 1 430 kg CO2 eqv./kg. The total amount of HFC-134a in NSB railway applications sums up to ~8 500 kg. This represents a global warming potential impact equivalent to ~12,155,000 kg CO2 equivalents. Deutsche Bahn has analysed the energy consumption of their Railway Rolling Stock in detail over several years. Up to 30 % of their total energy consumption has to be spent to operate the HVAC units of the passenger trains in Germany. Only the propulsion system requires a larger share of the total energy. In Norway, the energy consumption for heating up the train compartments is dominating, due to the high number of operating hours at low ambient temperatures. Therefore, it can be assumed that at least 30 % of the energy used by the public rail sector in Norway is spent to maintain comfort inside the passenger's cabins. The aim of the project is therefore the development of energy efficient and environmentally friendly HVAC units for trains together with leading industry players. R744 technology is regarded as a solution for the substitution of greenhouse gases in air conditioning applications in the railway sector. According to simulation results and based on previous experiences from other application areas, an improvement of the working figures for R744 systems can be expected by means of ejector support in cooling operation. It is, however, very difficult to make a precise assessment of possible improvements in overall performance. In practice, the actual overall efficiency will be strongly dependent on the individual components (compressor, ejector, heat exchanger). After completion of laboratory tests, the system was installed on a vehicle of the NSB flirt fleet in 2017. The design of the test carrier with two different circuit variants allows a direct comparison to the existing R134a system and between the two circuits. For this purpose, the two R744 circuits and a conventional R134a system are equipped with appropriate measuring technology on the vehicle. However, the control system received different control variables for R744 and R134a, preventing fair comparison and proper operation. During the project, it has been discovered that the market lacks appropriate heat exchangers for R744 at these conditions. The R744 system thus had challenges with the performance of the CO2/air heat exchangers, the integration of the expansion work recovery device (ejector) and the system control. As a consequence, producers of light-weight heat exchanger parts were contacted, and better heat exchangers and control systems will be developed and implemented in a follow-up project, granted funding, to improve the performance. The test campaign for the R744 system was conducted in Germany and the measurement results from the laboratory tests have been evaluated by SINTEF. The dual R744 air conditioning concept for the rail vehicle sector is developed in close collaboration between NSB, SINTEF / NTNU and Faiveley Transport Leipzig GmbH & Co. KG. This initiative is supported by the Norwegian Research Council.

Increasing the efficiency of the HVAC units by 20%, theoretically applied to all NSB passengers' trains, would reduce the annual electricity consumption by 20 GWh. The cooperation between FLT and SINTEF will trigger a technology shift related to HVAC units for European trains towards an elimination of applying working fluids harmful to the environment and a significant energy efficiency improvement. The research team in Norway will re-design the entire HVAC unit, applying advanced and detailed dynamic component and system simulation tools, in cooperation with FTL. The latest high efficient expansion work recovery units, ejectors, pre-tested and validated at SINTEF will be implemented in the R744 HVAC unit. The dual mode HVAC system will be able to utilize ambient heat even at -25°C ambient temperature to heat the passenger compartment. On the other hand the system will be able to perform safely and efficient at HVAC surrounding temperature of +50°C. The pilot unit will be assembled and tested in the laboratory of FTL prior the experimental testing on board of a NSB Flirt train. The 52 weeks testing period will allow validating simulation models and an optimization of the system controls, i.e. the HVAC unit can maintain the comfort level inside the passenger compartment at all time with a minimum of energy consumption. A state of the art HVAC unit, located in another coach of the same train, will be equipped with additional measurement equipment. Therefore, a scientific analysis of system performances under real operating conditions will be possible and direct system comparisons can be performed and documented. The results will be published in reviewed scientific international journals and conferences. Popular science articles will be supplied to trade magazines. Based on the results a phase out plan for the existing HFC HVAC units will be established to reach the strategic environmental goals of NSB. New trains to be ordered in 2016 should apply the new HVAC units.