How are passenger trains heated

Steam heating (railway)

The Steam heating is used to heat railway passenger trains in the cold season. A steam generator and a main steam line with steam heating couplings are generally required for operation. The steam generator is either located directly on the locomotive or in a heating car that is carried along. To supply parked or waiting passenger trains, there are preheating systems with stationary steam generators, for example in the form of parked heating locomotives. The steam heating couplings connect the main steam line between the locomotive and the car, as well as the lines between the cars. Freight wagons may only be parked at the head of passenger trains if they have a main steam line. The steam reaches the main steam line of the passenger car from the boiler via the steam heating couplings with a heating steam pressure of 3.5 bar. When the trains are preheated or in severe frost, the heating steam pressure is increased to up to 4.5 bar. Safety valves also limit the steam pressure generated by the boiler to around 5 bar.


High pressure and low pressure steam heating

A distinction is made between high pressure and low pressure heating. In the High pressure steam heating the main steam line is installed in the interior of the car. The temperature can be controlled through the inlet pressure of the boiler or with the help of shielding flaps. The Low pressure steam heating has a steam inlet regulator that feeds a steam / air mixture to the radiators inside the car. The steam inlet regulator also serves to discharge the condensate that is formed. In the case of the low-pressure steam heaters, control is carried out via a control valve in the passenger compartment; a thermostat can also limit the maximum temperature. The type of heater is written on the solebar of the passenger car in the form of abbreviations. It means:

  • Hhz 00– high pressure steam heating
  • Hhzk 0– high pressure steam heating with adjustable flaps
  • Nhz 00 - low pressure steam heating
  • Nhhz 0– Combined low pressure and high pressure steam heating
  • Nuhz 0– low pressure circulating steam heating
  • Nkohz - low pressure condensate heating

The steam heating was to be put into operation when the interior temperature of the passenger coaches was below 18 ° C, as well as during the internationally specified main heating period from September 1st to June 15th.

Types of boilers

For the diesel locomotives of the Deutsche Bundesbahn and the Deutsche Reichsbahn, the boiler types used were exhaust gas boilers with additional burners, smoke tube boilers and forced flow boilers. In detail these were:

In addition to supplying the train heating, these boilers also made it possible to heat the engine cooling water and the feed water. The cooling water is preheated to avoid a cold start of the diesel engine. To avoid the formation of scale, so-called conditioning agent is added to the feed water of the boiler. The dosage is based on a proof of dosage.

The locomotives listed above have a so-called three-circuit heat exchanger to keep the engine warm during the cold season and to preheat the engine's cooling water. In it, the lines of the engine cooling water, feed water and steam circuits are right next to each other and give off their heat from one another. This technical facility enables the locomotive to keep warm, as the three circuits give off their heat to one another until the temperatures are in equilibrium.

Energy efficiency

In theory, steam heating has an advantage, since in locomotives with internal combustion engines, energy can be drawn directly from the engine cooling system. However, the necessary pressures and temperatures around 160 ° C are not compatible with the cooling systems of the diesel engines, so that heat pumps or an additional burner are required.

Furthermore, due to the control technology, a certain "power surplus" must always be kept available, which is at least partially lost through the lines as heat loss.

Last but not least, in practice it is only very rarely possible to completely seal all connections; the result is a constant loss of steam, regardless of the required heating power.

The electrical heating by train busbar is theoretically less efficient - with diesel locomotives - but only the actually "burned" energy is fed in here. In the case of electric locomotives, the balance changes even more in favor of electric heating.

Risk of accidents

The steam temperature in the steam heaters of the rail vehicles is up to 160 ° C. Steam at this temperature can cause painful scalds. After closing the shut-off cocks of the steam heating couplings, the full heating steam pressure of up to 4.5 bar is still in them. Steam heating couplings may only be disconnected when they are depressurized. This is achieved by closing the steam supply from the locomotive in good time. Furthermore, the connection of the couplings must be opened carefully before disconnecting. Then the couplings must be pushed away in such a way that a gap is created between them through which any residual pressure can escape. Work or commissioning may only be carried out by trained personnel. The boilers are subject to the regulations for land steam boilers.

Individual evidence

  1. Orbits change frequency. In: Swiss Railway Review. No.11. Minirex, Lucerne 1995. p. 460.