eCitaro: Intelligent thermal management

E-mobility in series production

Temperature can not only be predicted, but also managed.

Due to the large interior, the huge window surfaces and the frequent opening of the doors, the interior temperature of a city bus is very energy-consuming. Since no usable waste heat is generated due to the high efficiency of an electric motor during operation, the total energy consumption of an all-electric bus can nearly double, especially during the heating season.

This high additional energy consumption has a clear impact on range. This is why the eCitaro’s sophisticated intelligent thermal management minimises energy consumption while ensuring maximum range. The interior can be preconditioned to the desired temperature as early as during charging in the depot. The passenger compartment is cooled by a standard roof air conditioning system with an energy-saving heat pump.

The passenger compartment of the eCitaro is heated in an energy-efficient way via the optimised CO₂ heat pump connected to the water circuit. This reduces the energy consumption of the electrical fan heaters on the side walls thereby enabling increased range in winter time. The well-known front box features a double heat exchanger. Optionally, a fuel-driven auxiliary heater can be used. The automated interior temperature, which depends on the outside temperature, is especially innovative. Here you can choose between an Eco and Comfort characteristic line. This leads to an increase in efficiency of up to 40 per cent.

Highly efficient heating through networking.

The design of the passenger compartment’s air conditioning system is based on the specifications of the Association of German Public Transport (VDA). The level of comfort in the outer limits, where ambient temperatures are either extremely hot or extremely cold, is adjusted. Instead of a predetermined absolute interior temperature, a defined reduction or increase to the external value is used. Thermal management has been optimised down to the last detail.

This means that all heat-emitting components are networked together to optimise the energy required for cooling. The performance of heating and air conditioning also varies depending on the number of passengers on board. This is determined via the axle load sensors.

Since the city bus passengers usually spend only a short time in the vehicle, this slight comfort limitation in favour of energy consumption and therefore range is perfectly reasonable. On the other hand, since drivers spend their entire work day in the city bus, their requirements are somewhat higher – especially recognising that maximum driver fitness needs to be safeguarded. With this in mind, the air conditioning of the driver’s work station is regulated separately and independently of the passenger compartment. Overall, the energy required for the eCitaro’s heating, ventilation and air conditioning is close to 40 per cent lower than for the current Citaro with an internal combustion engine.