Subodh Sagar, CWE, Central Railways( Centre) Felicitates Bapat (right) and Rajput (left).
Until the pandemic, most facility users were unaware and unconcerned about how the ventilation of closed spaces could affect their health and safety. Across all kinds of facilities, there are keen efforts now ongoing to clean and maintain HVAC systems to protect human health.
The Indian Railways has thousands of air-conditioned coaches under its purview, across sleeper compartments and special trains like Shatabdis and Vande Bharat train sets. Each of these coaches is air-conditioned, but how are the air conditioning units maintained? What challenges arise in their maintenance? What solutions are the Railways looking for?
Manish Bapat, Chief Electrical Engineer (Rolling Stock), CSMT, Central Railway and Rohit Rajput, Coaching Depot Officer, Lokmanya Tilak Terminus, Mumbai Division, Central Railway shared their expertise on maintaining coach air handling units and improving indoor air quality in rolling stock at the Clean Rail Conference – Zonal Meeting 1 at Mumbai. Here is a distillation of what they said:
Coach HVAC systems
The HVAC system of a train compartment consists of compact AC units, duct systems, exhaust air systems, circulating air duct system, air screens with filters, open/closed loop control devices and sensors.
The system is used for four purposes: heating, cooling, dehumidification and air filtering. Each roof-mounted unit has two distinct cooling systems. Fresh air from outside and return air from the coach are mixed and passed over the evaporator and blower drums, before being sent back into the ducting area. The supply duct system channels cool or warm air along the length of the entire compartment. If there are leakages in the duct system, contamination of the inside air may take place.
Fresh air screens are provided above the main door in the RMP unit. Fresh and recirculation air flaps are also provided.
Exhaust air units are installed in the roof at the end of each coach. A radial fan and air box are provided for this purpose, but they do not function very efficiently.
Role of sensors
LHB coaches have sensors to measure room temp, ambient air and supplied air, as well as hygrostats. Across the world, only these two parameters are measured in train compartments.
Whenever the temperature or humidity fluctuates beyond given limits, the microprocessor automatically kicks in to restore normalcy.
Fresh air intake of 20-30% is maintained. A relative humidity of around 60% needs to be maintained at all times; above this level, dehumidification begins. Cooling begins when temperatures exceed 28 °C.
Air quality issues
Poor indoor air quality in coaches is caused either by mechanical issues in the air conditioning system or deficiencies in fresh air intake.This can affect passenger health by causing respiratory issues, allergies and other problems.
Inadequate ventilation causes air to become stagnant, leading to the collection of dust and harmful gases inside the compartment. Nitrogen oxides from power cars and diesel engines are a problem in particular. Moulds may grow in the damp areas of the air handling units.
The quality of ambient air is the biggest determinant of indoor air quality. Filtering fresh air can help to some extent. Indian Railways is looking for HEPA filters that can filter out PM 2.5 effectively, and at a price that is reasonable. Trials can then be conducted to gather data on their effectiveness in train coaches.
Duct cleaning
When dirt in the ducting system is dislodged, it becomes a contaminant. Abroad, the average frequency of cleaning recommended for coach air ducts is every 3-10 years. Indian Railways cleans ducts every 1.5-3 years. Vande Bharat train sets already have UV lamps for disinfecting air.