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4. Modern cooling systems and their design Great demands are made on rail vehicle components today, combined with a high power density and reduced safety margins. New developments were fostered by new generations of vehicles for highspeed and commuter service. Availability targets and the competitive situation and the resulting cost pressure on manufacturers and operators played a major role in this process. Today’s cooling systems must offer the following features: • competitive and economical, • compact design with a high power density, • light and robust at the same time, • technically innovative, •low and precisely controlled auxiliary machine power (fans, pumps) in order to save energy, • long service life, • high availability, i. e. low maintenance, high reliability, trouble-free, • recyclable and environmentally compatible with regard to materials and consumables used and productionprocesses employed, •low noise emission [9, 10]. These requirements – some of which contradict each other – are detailed in tender specifications for new vehicles. Both vehicle manufacturers and end users expect a competent cooling system manufacturer to contribute his know-how to the vehicle design and offer solutions to possible problems. 16 Consequently, the cooling system manufacturer must be consulted already when drafting the tender specification at the project planning stage, especially with regard to the arrangement of components and the cooler group in the vehicle. The arrangement and properties of components often have a negative influence on their cooling, e. g. • insufficient space for cooling, • unfavourable routing of cooling air (outside and inside the cooler group), • problematic air intake and discharge conditions (dirt, leak air), • speed-dependent external pressure conditions due to the air flow around the vehicle, and • high auxiliary machine power. To achieve low noise emission levels, low costs, and high efficiency in the system, all parties concerned must examine and assess all possible options and influences. The consequences of changes and alternative solutions must be presented and the best solution for a given project must be found in cooperation. An example will show that this way of proceeding is both appropriate and successful. When designing a series of electric locomotives rated at 4 to 8 MW using standardized modules, various concepts and variants derived from them were calculated completely, both with regard to technical parameters and cost. Experts in the field of electrical driveline components (traction inverter, transformer, traction motors), vehicle construction, aerodynamics, accoustics, and cooling were involved. The following design variants were considered, among other things: - central cooling air intake with and without air cleaning for all consumers (inverter/transformer cooling, traction motor cooling, air-conditioning units, auxiliary equipment, machine compartment ventilation), - individual intake with air cleaning at the consumers that need clean cooling air, - combinations of different cooling devices vis-à-vis single or multiple arrangement with different types of redundancy and drive power. In order to achieve redundancy in air supply, additional measures had to be taken for the combination solutions, e. g. for cooling air supply by the sister unit. This required a high drive power, among other things due to high flow losses in air ducts and to the required flow restriction when matching the cooling air flows to the various consumers. Also assessed were the weight, space requirements, ease of installation, accessibility, noise emission, and damping requirements as well as the energy consumption of auxiliary machine systems. The assessment revealed advantages of combination solutions in the categories of space requirements and initial cost. However, these solutions later proved to be impracticable due to high operating costs for energy supply and high costs for redundancy. Partial combinations like those successfully used for inverter and transformer cooling, in contrast, came out well. This applies in conjunction with central air intake – with air cleaning and silencing facilities if necessary – and the possibility to have different segments for the various consumers. The examinations also showed that optimization of the total system should be given preference to cost reductions for individual components only. This applies even more to new vehicles as the demands made on them continue to rise.
5. Economical considerations Development costs money. It can only be financed today if there is a financing concept that is suitable for small lot production as found in the rail vehicle sector. Taking into account market appreciation of high-quality components would be desirable, but there are no signs that it might ever be possible under the current competitive conditions. There is a wide variety of fan types and designs available. Cheap offers are based on standard modules for different applications and will rarely be suitable for rail vehicles. Just comparing prices is not the way to find a suitable fan. An analysis of the price/benefit ratio and of life cycle costs is indispensable. The price difference of a few thousand Euro between a fan with a high overall efficiency of up to 90 % - such efficiency levels are possible by using slim blade profiles with optimum twist - and one of 50 to 60 % efficiency is often compensated by fuel savings already after two to three years. An example of a railcar with 480 kW engine output illustrates this. With a cooling requirement of 2 x 5 m 3 /s and a total pressure of about 1000 Pa, the use of high-efficiency fans permits fuel savings of about 2400 l/yr. (tables 4 and 5). Standard system Voith railway system Efficiency 55% 84% Power consumption ca. 9.0 kW ca. 6.0 kW Hydraulic pump * ca. 24 kW ca. 16 kW Table 4: Comparison of batch-manufactured standard cooling systems vis-à-vis special rail vehicle cooling systems. Fan design: Standard cooling system – plastics, aluminium (without fan shroud) Rail vehicle cooling system – aluminium (with fan shroud) * with 2 fans η Hy = 0.75 Assumption: • max. power of standard fan 24 kW • max. power of Voith fan 16 kW • max. savings 8 kW • Annual average savings about 30% 2.6 kW • 4 000 operating hours per year Energy savings: 2.6 kW * 4 000 h/year = 10 400 kWh/year Fuel savings: 10 400 kWh * 190 g/kWh ≈ 2 000 kg/year Table 5: Comparison standard fan / Voith fan 2 000 kg / 0.83 kg/l ≈ 2 400 liter/year This example shows that the fan as a dynamic element and aerodynamics are at least as important as the radiator element when optimizing the cooling system as a whole. Optimally tuned complete systems guarantee high efficiency and thus also maximum economy. Future vehicle concepts will have to take this into account. 17
Page 1 and 2: Fans in rail vehicle cooling system
Page 3 and 4: Summary Fans are a key component in
Page 5 and 6: specified working point (L in fig.
Page 7 and 8: 3.1 Drive and control Today, the dr
Page 9 and 10: Capacity of hydrostatic pump 1,0 0,
Page 11 and 12: temperature overlaps between coolan
Page 13 and 14: 3.4 Arrangement of the fan The vehi
Page 15: 3.6 Noise emission and sound insula
Page 20: 20 Voith Turbo GmbH & Co. KG Divisi

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