Essentials
SELELE MASHILO
Selele Mashilo has a mechanical engineering diploma from Tshwane University of Technology and
a refrigeration and air-conditioning diploma from Unisa. His experience includes over a decade in
government as deputy-director building services before rejoining the private sector in 1998 as HVAC&R
project engineer. He is the former chairperson of the Refrigeration and Air Conditioning Empowerment
Forum of SA (RAEFSA), the Air Conditioning and Refrigeration Industrial Council of SA (ACRICSA), and
Black Energy Services Companies (BESCO).
RAILROAD AIR CONDITIONING
By Selele Mashilo
Railroad cars are used in various areas where passengers are transported
from point to point over short or longer distances.
C
omfort 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.
grille will be under the evaporator with fresh air grilles above the
roof and not in front of the car.
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
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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. RACA
RACA Journal I February 2020
57