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Yes, many of them do. Indian Railways now provides an air conditioned locomotive cab on its high powered diesel classes, using a single compact unit mounted on the roof of the driver’s cabin. The unit delivers about 1.75 tonnes of refrigeration of cooling, which is comparable to one large domestic air conditioner. It operates on 74 volts of direct current drawn from the locomotive’s own auxiliary generator. New locomotives are supplied with the unit already fitted, and existing locomotives are being fitted in stages at diesel sheds.
The subject deserves more attention than it usually receives. A locomotive cab presents conditions that no domestic air conditioner is built to meet, and the demands Indian Railways places on this equipment reflect that in close detail.
This article sets out the essentials of the air conditioned locomotive cab in plain terms. A separate and fuller article covers the governing specification clause by clause, for readers who need that level of detail.
Quick Answers
What does an air-conditioned diesel locomotive cab use for its cooling?
An air conditioned locomotive cab uses one compact unit, built into a single housing and mounted on the cab roof.
What is its cooling capacity?
About 1.75 TR when the outside air stands at 35 degrees, and about 1.50 TR when it reaches 50 degrees.
Where does the power come from?
74 volts of direct current (DC), taken from the auxiliary generator of the locomotive.
Can it warm the loco cab too?
An electric heater is provided within the same unit for winter operation.
Which diesel locomotives have it?
WDG4, WDG4D, WDP4B and WDP4D.
Why Locomotive Cabs Reach High Temperatures
The case for an air conditioned locomotive cab begins with the heat itself. Heat reaches the cab from three sources at once, and each one is hard to avoid.
- The first is the roof. The cab roof is steel, it carries no shading, and it faces direct sunlight for the whole of a daylight duty.
- The second is the engine. A diesel engine of more than 4,000 horsepower sits just behind the cab, and an engine of that size gives off a great deal of heat.
- The third is the glass. A loco pilot needs a clear view of the track and the signals, so the cab carries large windows. Glass admits sunlight directly.
Together, these three sources raise the cab above the shade temperature outside. During a summer duty in western India, conditions in the cab become severe.
Why an Air Conditioned Locomotive Cab Is a Safety Matter
An air conditioned locomotive cab is sometimes seen as a matter of comfort alone. That view is too narrow.
A loco pilot must watch signals, check instruments and judge speed across a long duty. Each task calls for steady concentration. Heat stress is known to reduce both concentration and reaction time.
The Railway Board therefore treated cab cooling as part of safe working. The retro-fitment instruction issued by the Research Designs and Standards Organisation states the object in plain terms: to provide comfort to the cabin crew during train operation.
Why a Domestic Air Conditioner Is Not Suitable
The duty of an air conditioned locomotive cab cannot be met by adapting a domestic unit. Four conditions of railway service explain why.
Continuous vibration and shock
The unit meets engine vibration on every duty, shock from the track, and sharper blows during shunting. A domestic unit would not last a full season in that setting.
High dust concentration
Indian Railways runs across desert and dry terrain. The rules allow for dust levels that would block a domestic filter within days.
Severe space constraint
Every railway works to a set loading gauge. For this class the limit is 4265 millimetres. A locomotive above that height cannot pass under bridges or through tunnels.
The whole unit is therefore held to 350 millimetres above the roof line, which is about the length of a school ruler.
How an Air Conditioned Locomotive Cab Operates
An air conditioned locomotive cab does not make cold. The unit moves heat from one place to another.
The process works like a relay. A liquid called refrigerant takes up heat inside the cab and carries it to the roof. There it gives the heat up to the outside air, then returns for more. The cycle runs for as long as cooling is needed.
A domestic window air conditioner works on the same principle, which is why the back of an AC unit becomes hot during use.
The locomotive unit uses R-134a. The same refrigerant is used widely in car air conditioning.
Why the Motors Are of the Brushless Type
The unit contains motors that drive the fans and the compressor.
Direct current motors of the older type used small carbon blocks called brushes. These pressed against a turning part to pass current. The method worked, but the brushes wore down in service and had to be replaced from time to time.
The rules now call for brushless motors instead. In a brushless machine, electronics do the switching that the brushes once did.
Two results follow. There is no wearing part to check or replace, and no carbon dust forms inside a sealed box that already works in dust.
The same thinking applies to the drives. Belt drives and chain drives are not accepted. Each motor must be coupled straight to the fan or compressor it turns, because belts stretch and fail in service.
Cooling in Summer and Heating in Winter
Indian conditions are not hot all year. Winter mornings in the north can be very cold, and a cab that is only cooled would serve the crew for part of the year.
The unit therefore carries an electric heater rated at not less than 3 kilowatts, which is about the same as a large kettle.
The heating elements sit where the blower draws air in. Warm air is mixed before it enters the cab, so one side of the cab does not stay cold while the other is warm.
In cooling mode the unit maintains the cab between 24 and 27 degrees. In heating mode it maintains the cab between 21 and 23 degrees.
Frequently Asked Questions
Do all Indian Railways locomotives have air conditioned cabs?
No. The rules set out here apply to the high powered diesel classes WDG4, WDG4D, WDP4B and WDP4D. Locomotives of these classes built recently are supplied with the unit fitted. Earlier ones are being fitted in stages at diesel sheds, so the work is still going on. Other classes fall under their own separate rules.
Why does an air conditioned locomotive cab require such a compact unit?
Because the space on offer is very limited. The whole unit must stay within 350 millimetres of height above the roof. Any greater height would stop the locomotive passing under bridges and through tunnels.
Does the loco pilot control the temperature in an air conditioned locomotive cab?
Yes. A rotary switch offers five positions: Off, Vent, Cool, Heat and Auto. A digital display shows both the cab temperature and the outside air temperature.
What occurs if the unit fails during a run?
The design keeps the blower running even when cooling is suspended, so the cab still receives moving air.
Why is the housing manufactured from stainless steel?
Rainwater, salt laden coastal air and airborne dust all attack ordinary steel. Stainless steel of grade 304 stands up to them far better.
Is a locomotive cab unit the same as passenger coach air conditioning?
No. A passenger coach is served by two much larger units of 7.0 TR each. A cab unit is far smaller, because it cools the space used by two crew members rather than a saloon of seventy passengers.
Summary
- An air conditioned locomotive cab is served by a single compact unit mounted on the roof of the driver’s cab.
- The cooling duty is about 1.75 TR at an outside air temperature of 35 degrees, and about 1.50 TR at 50 degrees.
- The unit operates on 74 volts of direct current supplied by the locomotive’s auxiliary generator.
- All motors are of the brushless type, which removes a wearing part from the assembly.
- The same unit provides cooling in summer and heating in winter.
- Fitting an existing locomotive calls for an opening to be cut in the cab roof and a frame to be welded in place.
- A cooled cab supports crew alertness, and is therefore a safety matter as well as a matter of comfort.
The air conditioned locomotive cab is one part of a much wider field. Trans ACNR Solutions Private Limited works on climate control systems for railways, covering coaches, metro cars and locomotives.