SIEMENS

It's a summer day and Vienna's trams are packed. The air conditioning is running full blast. But the question is: does the AC really need to be set at maximum to ensure a comfortable ride? "In extreme cases, heating, air conditioning, and ventilation systems can account for 30 to 40 % of a tram's total energy use," says Dr. Walter Struckl, an expert on sustainable public transport systems at Siemens. That's ample reason to think about energy conservation.

There's no lack of ideas in this area, but the usefulness of such ideas depends on many factors. "Good insulation reduces the heating energy needed in winter, but it also increases tram weight, so it's not necessarily economical," says Struckl. "Tram ventilation systems are designed for maximum occupancy," he says, "but any incoming air also has to be heated or cooled. If you use sensors to calculate the number of passengers at a given time, however, you can provide the right amount of fresh air and still maintain optimal air quality."

So how can climate control be made energy efficient while at the same time keeping costs under control and satisfying passengers? To answer that question, Siemens, the Vienna University of Technology, local Vienna transport-related companies, consulting firm SCHIG mbH, and climate control system manufacturer Vossloh Kiepe teamed up in March 2010 to launch the Ecotram research project. The project will run for 18 months and is being funded by Austria's Climate and Energy Fund. "We're focusing here on heating, air conditioning, and ventilation because these systems account for a large share of energy consumption," Struckl explains. "Our project partners cover all pertinent technologies—from air conditioning units to climatic test labs and the production and operation of rolling stock."

Climate and ventilation systems for a state-of-the-art tram use about 100,000 kWh of electricity per year. The Ecotram project will show how much this figure can be reduced. Günter Steinbauer, the managing director of the city's transportation authority, believes it can be lowered by at least 10 %. Applying that figure to the city's 300 modern trams alone would yield annual savings of over 3,000 MWh, the equivalent of the electricity consumed by 1,200 households during the same period.

Ecotram partners plan to study the effectiveness of 20 energy-saving ideas. These proposals range from improved insulation to the use of waste heat, floor heating systems, and reflective exterior paints. Project manager Prof. Martin Kozek of the Vienna University of Technology's Institute of Mechanics and Mechatronics believes predictive control units can play a key role here. "If it's summer and you know a tunnel is coming, you can turn down the air conditioner and ventilate the tram with cool air from the tunnel. The tram runs the same route every day, so you can quickly achieve big energy savings," says Kozek.

Struckl believes a lot can be gained by using carbon dioxide sensors for air regulation, since CO₂ content provides an indication of how many passengers are on board. He's also thinking about the color of the light used to illuminate the trams. "With cold lighting, people feel like it's around two degrees cooler than it actually is. Using the type of lighting provided by LEDs, for example, would conserve a lot of energy because it would enable you to alternate between warm and cold-white colors as needed," Struckl says.

Many energy-saving measures are geared to specific situations, such as cooling a crowded car. That means they can be effective only if the given situation occurs frequently and/or causes the tram to use a lot of electricity. Ecotram experts are therefore measuring the energy balance of a tram in a climatic lab and under normal operating conditions. The resulting data flows into a program that manufacturers and operators will use to simulate tram thermal behavior on any number of different routes, enabling them to optimize the climate control systems.