Air Conditioning in Railway Coaches

Railway coaches require air conditioning systems with high reliability, light weight, and small size to function effectively and conveniently, utilizing available power sources and accommodating passenger flow and varying climates.

Railway coach air conditioning systems face challenges like high reliability requirements, limited space, fluctuating power supply (DC/AC), and varying ambient conditions.

Air conditioning systems on trains must be highly reliable to ensure passenger comfort and safety during travel.

Railway air conditioning equipment needs to be lightweight and compact to fit within the confines of a railway coach.

Railway coaches often utilize a mix of power sources, including DC and AC, due to power availability on different trains.

Air conditioning systems need to adapt to rapid changes in passenger numbers and temperature to avoid discomfort for passengers.

Railway coach air conditioning must manage extreme temperatures, vibrations, dust, vandalism, and safety concerns (e.g., ballast) within a limited maintenance timeline.

The evaporator unit has a thermostatic expansion valve, heat exchanger, resistance heater, and blower.

Controls refrigerant flow to match cooling demand.

Transfers heat from air to refrigerant, causing cooling.

Compresses refrigerant vapor, raising its pressure and temperature.

Multi-cylinder reciprocating compressor.

Removes heat absorbed by the refrigerant.

Forced-air-cooled by fans.

The refrigerant vapor comes from the evaporator.

Return air (75%) and fresh air (25%) are mixed for cooling.

Excessive pressure on the discharge side of the compressor.

The pressure at the compressor's inlet (suction side).

Ice forming on the evaporator due to low suction pressure.

Gradually increasing the compressor motor's power to prevent a surge in starting current.

A safety feature that prevents the heater from operating when the compressor is running.

Protects the compressor motor from damage by shutting it off if the voltage drops below a set limit.

The blower fan must start before the heater to prevent overheating.

A duct that brings fresh air into the railway coach.

The duct that draws back air from the coach, typically through filters.

Controls the amount of fresh air entering the compartment.

Multistranded PVC insulated copper cables conforming to ICF/Elect./857 specification are used.

This ensures easy maintenance and prevents fire hazards.

Crimped connections are used to ensure reliability and secure contacts.

Fire retardant FRP (Fiber Reinforced Plastic) material is used for terminal boards.

Mercury in glass thermostats with settings for cooling and heating control the temperature.

Two settings for cooling at 25°C and 23°C, and two for heating at 21°C and 19°C are currently used.

Electronic thermostats with one setting each for cooling (24°C) and heating (20°C).

Different coach types have varying passenger capacities, thus requiring different AC plant capacities.

A B.G.A.C. 1st class coach requires a 6.7 TR AC plant capacity.

A B.G.A.C. 2-tier coach needs a 5.2 TR AC plant capacity for each of its two plants.

The number of coaches determines the number of compressors needed. The total refrigerant amount depends on the number of compressors and the AC type, with higher amounts for full AC coaches.

Air-conditioned coaches have several maintenance schedules: Trip schedule, Monthly schedule, Three monthly schedule, and POH (Periodic Overhaul) - One year.

A typical POH (Periodic Overhaul) shop for AC coaches has a receiving shed, track, pit, and work sections for different equipment. It also has a wider line for final testing.

The receiving shed is used for unloading and loading equipment for AC coaches. It features a pit for accessibility.

Mechanized transport, such as forklifts, is used to move equipment around the POH shop efficiently.

Self-generating coaches use an alternator mounted on the bogie transom, driven by the axle. The alternator powers the coach when in motion above a minimum speed. During stationary or low speeds, a 800AH battery supplies power.

End-on generation coaches receive power from separate generator cars at the train's ends. 415V, 3-phase AC power is transmitted through inter-vehicular couplers.

SG coaches have provisions for pre-cooling using an external 415V, 3-phase AC supply. Two sockets are located on the end walls of the coach.

The alternator in underslung AC coaches produces 18kW at 130V DC. The RMPU AC coach alternator has a higher capacity, generating 25kW.

A battery with a capacity of 800AH powers the SG coaches when stationary or at speeds below the alternator's minimum output.

The power is transferred from generator cars to individual coaches using double feeders running along the coach and connected by inter-vehicular couplers.

A rotary switch is used in EOG coaches to select power from one of the double feeders running along the coach, providing redundancy.

Air conditioning equipment operates on a 415V, 3 phase AC supply.

A 3 KVA, 415/190V, 4 wire step down transformer reduces the main 415V supply to 110V for train lighting.

Self-generating coaches use DC motors for driving the air conditioning equipment.

E.O.G. type coaches use 3 phase AC squirrel cage induction motors for air conditioning.

BG AC 2T Sleeper coaches have one set of 800 AH batteries (56 cells) which comply with IS 6848.

The key components include the evaporator unit, compressor, condenser unit, gauge panel, A/C control panel, air duct, refrigerant piping & joints, and wiring.

Multistranded PVC insulated copper cables conforming to ICF/Elect./857 specification are used in air conditioned coaches.

Crimped connections are used throughout the wiring to ensure reliability and secure contacts.

The evaporator unit is responsible for cooling the air in a railway coach. It uses refrigerant to absorb heat from the air, leading to a decrease in the air's temperature. It consists of a thermostatic expansion valve, a heat exchanger, a resistance heating unit, and a centrifugal blower.

The compressor is the heart of the air conditioning system. It takes low-pressure, low-temperature refrigerant vapor and compresses it, increasing its pressure and temperature.

The condenser is responsible for releasing the heat absorbed by the refrigerant back into the environment. It typically uses fans to blow air over the condenser, cooling the refrigerant and turning it back into liquid form.

The blower fan is responsible for circulating the cooled air throughout the coach. It draws in air from the evaporator and pushes it out through vents, distributing the cool air to all areas of the coach.

The resistance heating unit is used to warm the air inside the coach when the outside temperature is low. It provides supplemental heating when the heat generated by the compressor is not enough.

The outside air temperature influences the cooling load on the AC system. If it's very hot outside, more cooling is needed, and the AC system has to work harder. If it's very cold outside, the heating unit may be used to maintain a comfortable temperature.

Filters in the air conditioning system prevent dust and other particulate matter from entering the coach through the fresh air intake and return air path. This helps to improve air quality and maintain passenger comfort.

A fluid that absorbs heat from the air inside a coach and releases it outside, creating cooling.

A unit of measurement for the cooling capacity of an air conditioning system.

A railway coach that has air conditioning in all compartments, requiring more compressors and refrigerant.

A railway coach with air conditioning only in some compartments.

The pressure on the discharge side of the compressor, which should not be too high to avoid damage.

Ice forming on the evaporator due to low suction pressure, which can reduce cooling efficiency.

Gradually increasing the power to the compressor motor to prevent a sudden surge in current.

The blower fan must start before the heater to prevent overheating.

A duct that brings fresh air from outside into the railway coach.

Filters placed in the air duct to remove dust and other particles from the return air.