The waste energy produced by under-floor traction equipment in MU stock can be used to heat passenger coaches. In many cases, the amount of thermal energy produced this way is sufficient to supply all the heating energy needed.

The use of waste heat can be realised by a heat exchanger (usually of the air-air type). This is already realised in modern DMU stock. In EMUs such a system is not yet implemented.

A more sophisticated method to make use of waste heat from traction equipment for comfort functions is based on the ORC principle. Such a system which is not yet realised in railways would permit to produce power for electric comfort functions from waste heat.

The use of waste heat by means of heat exchangers is already realized in many modern DMUs but not yet in EMUs.

Energy saving

While for DMUs, the use of waste heat by means of heat exchangers is already implemented in some modern stock and barriers for a further diffusion are low, the extension of the measure to EMUs meets the following barriers:

Complexity

Compared to DMUs, the heat sources in EMUs are less concentrated along the train: motors, transformers and inverters are distributed along the entire train length. Furthermore the temperature of the individual heat source is relatively low (e.g. some 80-120 °C in the case of electric traction motors). To use this heat in an effective way requires a relatively sophisticated concept for the air flow of the heat exchanger. This will increase initial and maintenance costs as well as liability to defect.

The use of waste heat from traction equipment on the basis of heat exchangers is only feasible for MU stock because waste heat cannot be transported along the train.

DMUs: use of waste heat from traction equipment is a common feature in modern stock.

EMUs: not yet in use.

According to DSB, the amount of waste energy produced is mostly sufficient for heating in all seasons. Given that comfort functions account for about 20% of total energy demand for passenger train operation and the fact that the power for lighting and cooling cannot be supplied by such a system, the saving potential will be between 5 and 10 %.

Especially in EMUs, where the use of waste heat is not yet realized, there would be clear scale effects in the initial introduction phase.

The use of waste heat from traction equipment is a promising strategy to reduce the energy demand of comfort functions. In DMUs the measure is becoming a standard in new stock. A corresponding solution for EMUs meets more technological challenges and has not been developed yet. More R&D efforts for EMUs are justified since even for electric stock the energy efficiency potential is promising.