Mumbai's first AC local could leave for Mumbai on October 2

The strongest air-conditioning units in the Indian Railways — to be installed in the first AC local for Mumbai — have been given the provisional clearance by the railways' apex technical authority. The move by the Research Design Standards Organisation (RDSO) will pave the way for the Integral Coach Factory (ICF) in Chennai to fit two such units in a coach and then test it in real time.

The rake will have 24 units in all — two each for the 12 coaches — and once the trials for the first two are over, officials said, the other 22 units should be in by September.

As of now, railway officials told dna, the most likely date for the rake to leave ICF and move towards Mumbai is October 2, Gandhi Jayanti. However, officials added, they are trying to see if the turn-out — railway lingo for sending a new train to the end-user — can be done earlier.

"Apart from being of a higher category than AC units currently in use on the Indian Railways, these units will have some new designs in its compressor. These are things which will have to be tested thoroughly. Mumbai is a peculiar case because of the kind of crowds that use local trains during peak hours. The density per square metre can go up to 16 people. The air-conditioned rake has to be something unique," said a railway official.

At 15 tonnes each, these air-conditioners — called Roof-Mounted Packaging Units (RMPUs) in rail lingo — will be much more effective than the 10-tonne RMPUs, the highest on Indian Railways, installed in the newly-built double-decker rakes and some trains of the Kolkata Metro. Most of the trains on Indian Railways, including the Rajdhani, have RMPUs of seven tonnes, said officials.

Tonnage in air-conditioning
In air-conditioning, a ton is the cooling capacity or heat-removal capacity of an AC unit. One ton — written as 1 TR — means the cooling effect equivalent to convert one ton of water into ice at the same temperature. It is measured in terms of British Thermal Units (Btu) and a one-ton air conditioner is rated at 12,000 Btu per hour. A Btu is the mount of heat required to increase the temperature of a pint of water (which weighs exactly 16 ounces) by one degree Fahrenheit. Higher the tonnage of an AC, the greater its cooling capacity.

What's expected from the 15-ton AC units
It must supply 0.14-metre cube of fresh air per person per minute.
Total fresh air supplied into the coach should be 70-metre cube per minute.
It should be able to work when the coach is crowded with up to 500 passengers.
It should bring relative humidity within a coach to about 60%.
It should be able to work when outside temperature is anything up to 40 degrees Celsius.
It should be able to work when train is travelling at 120 kmph.