This work is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License ePrints-Newcastle University ePrints http://eprint.ncl.ac.uk Sustainable urban rail systems: strategies and technologies for optimal management of regenerative braking energy

There is increasing interest in the potential of urban rail to reduce the impact of metropolitan transportation due to its high capacity, reliability and absence of local emissions. However, in a context characterised by increasing capacity demands and rising energy costs, and where other transport modes are considerably improving their environmental performance, urban rail must minimise its energy use without affecting its service quality. Urban rail energy consumption is defined by a wide range of interdependent factors; therefore, a system wide perspective is required, rather than focusing on energy savings at subsystem level. This paper contributes to the current literature by proposing an holistic approach to reduce the overall energy consumption of urban rail. Firstly, a general description of this transport mode is given, which includes an assessment of its typical energy breakdown. Secondly, a comprehensive appraisal of the main practices, strategies and technologies currently available to minimise its energy use is provided. These comprise: regenerative braking, energy-efficient driving, traction losses reduction, comfort functions optimisation, energy metering, smart power management and renewable energy micro-generation. Finally, a clear, logical methodology is described to optimally define and implement energy saving schemes in urban rail systems. This includes general guidelines for a qualitative assessment and comparison of measures alongside a discussion on the principal interdependences between them. As a hypothetical example of application, the paper concludes that the energy consumption in existing urban rail systems could be reduced by approximately 25-35% through the implementation of energy-optimised timetables, energy-efficient driving strategies, improved control of comfort functions in vehicles and wayside energy storage devices.

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License Newcastle University ePrints-eprint.ncl.ac.uk

Agriculture and Engineering, Newcastle upon Tyne NE1 7RU, UK * Contact: paul.batty2@ncl.ac.uk; +44 (0) 191 208 8657 Abstract Continued urbanisation, and the resultant increase in urban trips, presents one of the greatest challenges to the environmental, economic and social sustainability of society. Given that the modal split between transport modes has remained relatively unaltered in recent decades, this suggests that the levels of private car usage will lead to even greater levels of congestion and air pollution in urban areas. Therefore, a modal shift from private to public transport needs to be effected with urgency. However, whilst in theory this could be achieved with relative ease, numerous societal, political and economic barriers have thus far prevented such a shift from occurring. These have been analysed in detail, using a holistic approach which simultaneously considers all stakeholder needs. Recognising that traveller opinions and requirements are fundamental in effecting modal shift measures, the effects of public transport quality attributes on encouraging modal shift are discussed, accompanied by an updated version of the UK Department for Transport's hierarchy of public transport needs. This investigation then proceeds to analyse the effectiveness of methods to control urban car usage, before discussing solutions to address the barriers to a notable, successful modal shift, including guidance on how to design modal shift programmes. This paper provides useful and insightful guidance for all those involved in attempting to evoke sustainable mobility through a modal shift to public transport systems.2

a b s t r a c tAn understanding of electricity consumption due to residential air conditioning (AC) may improve production and environmental impact strategy design. This article reports on a study of peak and seasonal electricity consumption for residential air conditioning in the region of Madrid, Spain. Consumption was assessed by simulating the operation of AC units at the outdoor summer temperature characteristics of central Spain. AC unit performance when operating under part load conditions in keeping with weather conditions was also studied to find cooling demand and energy efficiency. Like wise final electricity consumption was computed and used to calculate energy costs and greenhouse gas emissions (GHGs). Cooling demand, when family holidays outside the region were factored into the calculations, came to 1.46 Â 10 9 kWh. Associated seasonal electricity demand was 617 Â 10 6 kWh and seasonal performance of AC units around 2.4. Electricity consumption in the whole region was observed to peak on 30 June 2008 at 5.44 Â 10 6 kW, being the load attributable to residential AC 1.79 Â 10 6 kW, resulting about 33% of the total peak consumption. The seasonal cost per household was about V156 and the total equivalent warming impact was 572 Â 10 3 t CO 2 . The method proposed can be adapted for use in other regions.

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This work is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License ePrints -Newcastle University ePrints http://eprint.ncl.ac.uk Experimental assessment of the energy consumption of urban rail vehicles during stabling hours: influence of ambient temperature