By Selele Mashilo
Railroad cars are used in various areas where passengers are transported from point to point over short or longer distances.
Comfort of the passengers is a priority, and air conditioning plays a major role. Not all rail cars are provided with windows for natural ventilation.
There are many engineering challenges on air conditioning system design to achieve acceptable comfort levels, but a lot has been done. Rail cars are built differently, and more than one car is used at the same time. Various power supplies are used which affects air conditioning system operation. The power supply may be either DC or AC type, and that determines the design of the car. Mechanical cooling capacity ranges from 26 to 28kW for a 26m-long car; imagine the location and weight of mechanical equipment.
Equipment selection
The source and type of power dictates a particular type of air-conditioning equipment system to be used. Power can be supplied from car axle driven generators. Where large batteries provide DC power, converters to AC power will also be required. Air conditioning compressors may be DC or AC power driven. The DC motors are larger than AC motors and larger space inside or outside the car must be provided. The first cost as well as operating cost and maintenance are taken into consideration during the design stage.
Therefore, it is necessary for coordination to take place in advance before the rail car is built. The interchangeability of coaches and sleepers should also be considered, since they should be able to operate at various places under various conditions.
Design limitations
Air-conditioning system design is dictated by space inside and outside the railroad car. Think about a space required by a 26kW air-conditioning plant, the physical size of the compressor, the condenser, evaporator and piping layout. The piping may run over a 25m length. The final positioning of mechanical equipment will be under the car for compressor and condenser. The condenser will be subjected to a lot of dust. The evaporator and supply ducting will be above the ceiling of the car roof. The return air grille will be under the evaporator with fresh air grilles above the roof and not in front of the car.
Equipment design
Equipment design and capacity will depend on calculated heat load of the car.
- Transmission load – based on typical material for outside, interior finishes, ceiling type and floor of the car;
- Sun load – the railroad will be exposed to the sun on one side and the roof while in motion and the total sun load is based on one side of the car and roof;
- People – this is the sensible load and latent load of maximum people in the coach;
- Electrical – based on sensible load of lights used; and
- Outdoor air ventilation – based on 25% of the total supply air.
System requirements
Refrigerant piping will run from the evaporator to the outside condenser. Suitable provisions for routes are critical. Air conditioning equipment should be installed on anti-vibration mountings.
