Hotel power

8911 at Connolly, originally uploaded by rowanC82.

"Hotel power" is the name given to the electrical power used to run things like heating and air-conditioning systems on trains. Each type of vehicle has what is known as an electric train heating (ETH) index. Typically, the power consumption of a modern air-conditioned vehicle is about 20kW per vehicle. The power consumption of each type of stock is expressed as a figure known as the ETH index. Mark 3 stock has an ETH index of 6, stock without air conditioning has an ETH index of about 3.

The power to run the heating and ventilation system is normally drawn from the locomotive and with electric traction, the power comes from the overhead line. With diesel traction, it is taken from the traction current generator on the locomotive.

In the case of mark 3 hauled stock, the power supply is run down the train via a 1000V DC line. In the case of HST trailer cars the power supply is 415V 3-phase. The locomotive must, of course, be able to deliver sufficient power to run the services in all the vehicles in the train. Freight locomotive types such as class 66 do not normally have the ability to provide ETH power.

An alternative is to use a generator van, which is the practice in Ireland (above). There were, at one time, an number of generator vans in mainland Britain, which could be used to enable HST sets to be hauled by locomotives. If generator vans are used, modern air-conditioned stock can be hauled by any type of locomotive, including all types of freight locomotive and even steam locomotives.

Electric train heating is not particularly efficient due to thermodynamic losses. With steam traction, the heating was direct from the boiler and in some cases by waste steam, which avoided these losses.

One way of avoiding thermodyamic losses would be to provide the hotel services on each vehicle with a mini-CHP (combined heat and power system). If my calculations are correct, it is about three times the power of a large portable generator and a de-rated motorcycle engine of about 200 cc would deliver what is needed. An engine and generator of the necessary power would weigh about 200kg. Whether the efficiency savings would be worth the trouble of having to carry the units around, maintain them, and keep the fuel tanks filled is another question. Vehicles fitted with such equipment would certainly have the advantage of flexibility. It is an idea that could be worth looking into.