Railway Coach Air Conditioning PDF

___________________________________________________________________________ 5. AIRCONDITIONING OF RAILWAY COACHES 5.0 INTRODUCTION Passengers in a railway travel are adversely affected by infiltration of air unpleasantly laden with dust due to open windows. This is more so in case...

___________________________________________________________________________ 5. AIRCONDITIONING OF RAILWAY COACHES 5.0 INTRODUCTION Passengers in a railway travel are adversely affected by infiltration of air unpleasantly laden with dust due to open windows. This is more so in case of high speed passenger carrying trains. Secondly for a tropical country like India, the temperature varies from 46 degree C during summer to 2 degree C during winter. Airconditioning of railway coaches is, therefore, necessary for the maximum comfort and well being of passengers in a railway travel. In keeping with modern trend, airconditioning of coaches for upper class travellers and lately even for lower class travellers has been introduced by the Indian Railways. 5.1 SPECIAL PROBLEMS FACED IN RAIL AIRCONDITIONING As compared to the normal buildings, Air conditioning of Railway coaches poses the following additional problems: Requirement of very high reliability standard. Equipment should be light in weight. Equipment should take minimum space. Available power, generally at 110V D.C. has to be utilised. 415 V, 50 Hz, 3 Ph, industrial power is available only on a few nominated trains like Rajdhani and Shatabdi Express. However, in such cases, the flexibility of attaching and detaching coaches is lost. Due to large number of passengers in small space, the space left for air circulation is limited. In the Railway coaches, where people move in and out at all hours of the day, to sudden changes in temperature, which may cause chill or heat are to be avoided. Rapidly changing ambient conditions as the train moves from one part of the country to another. Excessive vibrations. Dusty atmosphere. Vandalism and abuse. Flying ballast hitting the equipment. Safety of passengers and trains. Dirty environment for the maintenance staff. Restricted time available for maintenance. All these problems have to be solved,' within a comparatively small outlay, so that ________________________________________________________________________ ___________________________________________________________________________ airconditioned travel can become more common 5.2 REQUIREMENTS OF RAILWAY COACH AIRCONDITIONING SYSTEM Supplying clean fresh air at a controlled uniform temperature. Catering, within the confines of the Railway carriages to the continuously changing number of passengers. Providing for heating as well as cooling on a train that travels through areas of widely differing climate during its journey. Operation of the equipment from power generated, stored and controlled on the train. 5.3 CLASSIFICATION OF AIRCONDITIONED COACHES SG Coaches EOG Coaches BG MG ` AC AC AC Compo 1st AC 2T 3T 2T Chair site ACC Car AC AC AC 1st Pantry Dining Power 3T 2T Chair ACC Car Car Car 5.4 DESCRIPTION OF POWER SUPPLY 5.4.1 SG Coaches The electrical power for the self generating type of coaches is derived from the alternator mounted on bogie transom of the coach and driven by the axle through 'V belt drive as long as the coach is in motion at the minimum full load output (MFO) speed of the alternator. During stationary or when the coach is running at less than MFO speed the entire coach load is met by the battery of 800 AH capacity. Provision for charging and precooling the coach from external supply has been made by means of battery charger, 200A rating mounted on the coach under frame. Two numbers of 415 V, 3 ph, ac, precooling sockets have been provided diagonally on the end walls. The alternator working in association with rectifier cum regulator gives an output of 18 KW at 130 V, DC in the underslung type of AC coach, whereas the alternator capacity is 25Kw in the RMPU AC coach. One alternator set per AC plant has been fitted in the self generating type AC coaches. 5.4.2 EOG Coaches ________________________________________________________________________ ___________________________________________________________________________ The electrical power supply for end on generation type AC coaches is derived from separate generator cars marshalled at the ends of the train formation, with generation and transmission voltage of 415 V, 3 ph, AC. The power for individual coaches is tapped by means of rotary switch from any one of the double feeders running along the coach leading from the power cars, and coupled between coaches by means of inter-vehicular couplers. The airconditioning equipment works at 415V, 3 phase AC supply and train lighting equipment work at 110V, AC, obtained between phase and neutral derived from a 3 KVA,415/190V, 4 wire step down transformer. 5.5 DRIVING EQUIPMENTS Driving equipments consist of motors for driving the compressor, condenser impeller fans and the evaporator blower fans. The driving motors in self generating type coaches are all of D.C. machines needing more care for attention of commutator and brushes. The E.O.G. type coaches are provided with 3 phase AC squirrel cage induction motors for driving the AC equipments. 5.6 DETAILS OF BATTERIES PROVIDED ON S.G. COACHES (UNDER SLUNG TYPE) Type of AC Coach No. of sets & capacity Relevant BIS of battery specification BG AC 2T Sleeper 1 set of 800 AH (56 cells) IS ; 6848 BG AC Chair Car - do - - do - BG AC composite - do - - do - BG.ACC. 1st class. 1 set of 525 AH - do - MG.AC. 2T sleeper 1 set of 450 AH - do - 5.7 A/C EQUIPMENT IN RAILWAY COACHES This consists of the following: Evaporator Unit. Compressor. Condenser Unit. Gauge panel. A/C control panel. Air Duct. Refrigerant piping & joints. Wiring. ________________________________________________________________________ ___________________________________________________________________________ ________________________________________________________________________ ___________________________________________________________________________ ________________________________________________________________________ ___________________________________________________________________________ ________________________________________________________________________ ___________________________________________________________________________ ________________________________________________________________________ ___________________________________________________________________________ 5.7.1 Evaporator Unit The evaporator unit consists of a thermostatic expansion valve, a heat exchanger, a resistance heating unit and centrifugal blower driven by a motor The thermostatic expansion valve controls quantity of high pressure liquid refrigerant and allow to expand to a lower pressure corresponding to the load demand The expanded refrigerant passes through the distributor into the heat exchanger consisting of finned copper tubes. The return air from the air conditioned compartment (75 %) is mixed with fresh air (25%) and this mixture is drawn/blown through the heat exchanger, where heat in the air is transferred to the cool refrigerant causing cooling of the air and the evaporation of the refrigerant inside the tubes. The cooled air is led through the ducting to the various compartments and diffused by means of air diffusers Filters are provided in the fresh air and return air path to eliminate dust. When the outside ambient temperature is very low, heater is switched on according to the setting of the thermostats. 5.7.2 Compressor The refrigerant vapour drawn from the evaporator is compressed by means of a multi cylinder reciprocating compressor and compressed to a pressure ranging from 10 to 15 Kg/Cm2 according to the load demand. The work done due to compressor raises the temperature of the refrigerant vapour. 5.7.3 Condenser The condenser serves the function of extracting the heat absorbed by the refrigerant vapour in the evaporator and the heat absorbed during the compression process. The condenser consists of a heat exchanger, which is forced-air-cooled by means of two or three axial flow impeller fans. The refrigerant vapour is liquified when ambient cool air is passed through the heat exchanger. The refrigerant liquid leaving the condenser is led into the liquid receiver from where it proceeds to the expansion valve on the evaporator. The liquid receiver is a cylindrical container which contains a reserve of the refrigerant liquid. A dehydrator and filter are also provided to ensure that the refrigerant is free from moisture and dust particles. 5.7.4 Gauge panel Gauge panel consists of pressure gauges (HP, LP, and OP) and pressure cutouts to protect the compressor against, (i) High pressure, (ii) Low pressure and (in) low oil pressure. 5.7.5 High pressure cutout It is a safety device against build up of excessive delivery pressures and protects the compressor and piping system from damage. It is a pressure operated switch which switches off the compressor drive motor when the pressure exceeds a preset value ( 17.6 Kg/Cm2). The plant can not be restarted unless the cutout is reset manually. 5.7.6 Low pressure cutout ________________________________________________________________________ ___________________________________________________________________________ It is also a pressure operated switch similar to the H.P. cutout switch, but it shuts down the compressor if the suction pressure drops down below 0.7 Kg/Cm2. It protects the system against unduly low evaporator temperatures and formation of frost on the evaporator. No manual reset is provided on this and therefore the compressor starts automatically if the suction pressure rises above the preset value. 5,7.7 Low oil pressure cutout It ensures adequate lubrication of compressor to avoid piston seizure due to less lubricating oil or failure of oil pump. This cutout is set at 2.5 Kg/Cm2. 5.7.8 A/C control panel The control of the airconditioning system is achieved by means of air conditioning control panel. The design of the various elements in the control panel takes into account the system safety requirements. The safety requirements for the operation of the A/C system are listed as under: a. The working of blower fan of the evaporator and the blower fan of the condenser have to be ensured before the compressor starts functioning. b. Suitable protection to ensure adequate lubrication of compressor to avoid piston seizure. c. The excessive pressure on the discharge side of the compressor (High Head Pressure) should be avoided. d. The suction pressure should not be lower than 0.7 Kg/Cm2 to prevent frosting of the evaporator. e. The compressor motor has to be soft started to limit the sudden in rush of starting current. f A suitable interlock has to be provided to ensure that heater is not on, when the compressor is working. g A low voltage protection for compressor motor to ensure that voltage does not go below 100 volts in order to avoid undue drain on battery. h. The blower fan has to come 'ON’ before the heater comes 'ON'. Over load protection and short circuit protection for all electrical circuits. The A/C control panel incorporates all the above safety requirements. 5.7.9 Air duct The air conditioning system includes three air ducts as follows: a. Fresh (Inlet) air duct. b. Main air duct. c. Return air duct. Actually there is no separate return air duct provided in A/C coaches. In the case of ________________________________________________________________________ ___________________________________________________________________________ a.c. two tier coach and A.C. chair car, the return air is drawn through the return air filters directly from the nearest compartment In 1st class A.C. coach, the corridor acts as return air duct and the return air is drawn through return air filters located at the corridor ceiling near the first compartment. Fresh (Inlet) air duct This is provided at the rate of two per AC plant. It is mounted on the side wall just ________________________________________________________________________ ___________________________________________________________________________ below the roof evaporator unit. There is an opening in the side wall with louver hinge door arrangement and with the provision to house a fresh air filter. The fresh (inlet) air duct has been designed with damper valve to control the quantity of fresh air to be drawn into the compartment. This arrangement has been standardised for all types of air conditioned coaches Main air duct The conditioned air from the evaporator unit is blown into the main air duct by means of two centrifugal blower fans driven by a motor with double extended shaft, The air is distributed to each compartment in the case of 2 tier sleeper coach and full AC first class coach through adjustable diffusers. In the case of a c chair cars, the conditioned air from the main air duct is distributed along the hall through longitudinal apertures suitably set at factory. The main air duct has been provided with central diagonal partition making it two independent taper ducts so that each compartment is influenced by the diffused air of both plants. Further air distribution to the entire compartment is maintained at constant velocity. The cross section of the main air duct has been designed in such a way that air velocity inside the duct shall not be higher than 350 metre/min. in order to reduce turbulence and noise due to air motion in the duct. For the same reason the main air duct has been connected to evaporator outlet by means of an intermediate transition duct made of fire resistant canvas to prevent transmission of noise produced by the blower unit- The aperture of air diffuser has been designed to deliver the required quantity of air into the compartment at a velocity not greater than 250M/min. This diffuser is provided with a knob to deflect the air to the required angle. By the above arrangement the air velocity inside the compartment obtained is between 6M/min. to 12M/min. (0.1 M/sec. to 0.2M/sec.) at the face level of the passenger. 5.7.10 Refrigerant piping and joints The refrigerant piping consists of the suction line (from the evaporator out let to compressor inlet) discharge line (from compressor outlet to condenser inlet) and liquid line (from the liquid receiver to the inlet side of expansion valve), connections to the gauge panel from the compressor delivery side (high pressure side), low pressure side and from the compressor crank case. The lubricating oil connections are also part of the piping system Only copper pipes to specification BS:2017-63, C-106 Sec - 3 are used. Main pipelines are jointed with couplers or elbows by means of silver brazing where as joints to various components like gauges pressure cutouts, hand shut off valves, expansion valve, strainer etc. are connected by means of flare joints to facilitate easy removal of the above elements for replacement and inspection. 5.7.11 Wiring ________________________________________________________________________ ___________________________________________________________________________ All wiring has been done by means of multistranded PVC insulated copper cables to specification. ICF/Elect./857. All cables have been laid on steel trough/conduits for easy maintenance and prevent fire hazards. Crimped type of connections have been adopted throughout. All the terminal boards are of fire retardant FRP material, Reliability of wiring has been made very high. 5,7.12 Temperature setting The temperature inside the airconditioned compartment is controlled by mercury in glass thermostats with different settings as mentioned below. Operation of cooling or heating takes place in accordance with ambient conditions. The temperature control thermostats are fitted in the return air passage. Two types of thermostats are used, one for controlling the cooling and the other for controlling the heating. Both these thermostats are alike, each consisting of a sealed glass tube containing a column of mercury. Presently there are two settings for cooling at 25OC and 23OC and for heating at 21OC and 19OC respectively. The mercury thermostats are being replaced by electronic thermostat with one setting each for cooling at 24OC and for heating at 20OC. 5.8 CAPACITIES OF A/C PLANTS PROVIDED IN VARIOUS TYPES OF COACHES Sr. Type of Coach. No. of Calculated A.C. Capacity of A.C. No A.C. Plants load of coach. Plants provided. 01. B.G.A.C. 1st class. 01 01 5.30 TR 6.7 TR x 1 02. a. B.G.AC 2 tier. 02 02 7.48 TR 5.2 TR x 2 b. B.G.AC composite coach. 02 02 7.97 TR 5.4 TR x 2 03. B.G.AC chair car. 02 02 11.10TR 6.7 TR x 2 04 B.G.AC.3Tier 02 02 6.6 TR x 2 05. M.G.AC 2 tier. 01 01 6.39 TR 6.7 TR x 1 5.9 QUANTITY OF REFRIGERANT REQUIRED FOR VARIOUS TYPES OF COACHES ________________________________________________________________________ ___________________________________________________________________________ Sr. Type of Coach. No. of AC Plant capacity Types of Quantity No. Plants (TR) Compressor Refrigerant (kg.) 01. 1CF built full AC One 5to9 5F30 1x15 Coaches 5F40 (approx.) 5F60 SMC.4.65 FK4. 02. ICF built full AC Two 10tol8 5F30 2x15 Coaches. 5F40 (approx.) 5F60 SMC.4.65 FK4. 03. Partial AC Coaches One 2 5to3.5 5F20 1 x 12 FK4 (approx.) CP3 5.10 MAINTENANCE SCHEDULE FOR AIRCONDITIONED COACHES 5.10.1 The following are the various maintenance schedules carried out on air-conditioned coaches. Trip schedule. Monthly schedule. Three monthly schedule. POH - One year 5.10.2 Recommended standard facilities for POH of AC coaches Fig shows a recommended layout of a POH Shop with an out-turn of 5 coaches per month. The layout envisages the following flow of work. The layout incorporates a receiving shed with a pit of 1.35 M width, 1.3M depth and 30 M long to facilitate unloading/loading of equipment. Track and pit centre line are located 1 M off from the shed centre line. The equipment unloaded from the coach may be moved to the respective sections of the shop by means of mechanised transport facilities. After completion of overhaul work, equipments may be loaded on the coach kept in the receiving line and then the coach shall be brought to the shed having wider line with a pit of 5 M width for final testing and detailed examination of underframe equipment. ________________________________________________________________________ ___________________________________________________________________________ ________________________________________________________________________ ___________________________________________________________________________ 5.10.3 Standard facilities for POI1 of AC coaches Requirements for the pit For loading and unloading facilities, the pit width shall be 1.35 m (0.50 in M.G.), length 30m and depth 3m w ith steps on both side. For detailed exam /testing of underframe equipments, a pit having a width of 5m shall be provided. The walls of the pit shall be watertight. The pit floor shall have slope of 1 in 300 towards one end with sump Suitable pump shall be provided for pumping out water from the pit. Water tight fittings shall be provided in the sides of the pit at intervals of 6m. 24 V D C two pin sockets 3 Nos in each side of the pit for hand lamps. The wider pit shall be provided with 2 D.C. motor drives of capacity 25 KW each for testing of Alternators. 5.10.4 Final testing of A/C coach after POH Visual inspection of coach for proper fitment of equipments. Ensure the refrigerant pipes are properly clamped. Suction pipe for proper lagging. Ensure all the modifications are complied. Check safety chain and tension rod of B.L. Alternators for proper fitness. Underframe cables leading to Alt. are properly cleared. Check earth leakage by two lamp method. Check refrigeration system for any leakage before gas charging, a. Vacuum test ( for 12 hrs.) b. Pressure test ( by charging Freon 12 or CO2 gas). Vacuum test for 15 minutes for dehydration of refrigeration system. Check control panel and ensure that proper fuses are provided. Check contactors, relay and switches for correct sequential operation. Ensure that time delay in operation of contactor No.12, 13, 13A is 2.5 sec. Check heaters for correct operation. (Remove short between 1H 3 - 1H 4) Check hooter for proper operation. Start the plant and check condenser motor, compressor motor, blower motor for any abnormality, Check leakage of air from doors Check oil level in compressor, the level should be when operating - 1/2 bull's eye. Check for proper working of capacity control solenoid valve. Run the plant for 4 hrs. An equivalent heat load (Convector heater) should be kept for performance test of plain If new expansion valve is provided during POH, it be set. Ensure that batteries are in fully charged condition. ________________________________________________________________________ ___________________________________________________________________________ Take coach on trial run. Alternately test the alternator, regulator and AC plants for proper working with the help of variable speed drives in the shops itself. Ensure that both the alternators are sharing load equally during run. If not set both the alternator panels. 5.10.5 General checks Suction pressure gauge reading should be 2.6- 2.8 Kg/Cm2. Delivery pressure gauge reading should be 10 - 12 Kg/Cm2. Oil pressure should be minimum 3 Kg/Cm2 above suction pressure. Feel temperature - Suction should be cold and sweaty. Delivery should be very hot and liquid line should be warm. 5.10.6 Problems in AC coaches Gas leakage in pipeline from joints in the control equipment. Premature failure of shaft seal of compressor. High heat in condenser leading to leakage of refrigerant. Difficulty in cleaning of condenser. Vee belt failure. Compressor motor failure. Condenser motor failure. Dehydrator defective. PCB defective in regulator. 5.10.7 Service trouble 1. HP cut out operates due to - Malfunctioning of the cutout Condenser fan motor failure. Condenser fins and tubes dirty Any stop valve is closed or partly closed. Freon gas over charged. Air in the system. 2. LP cut out operates due to - Malfunctioning of LP cut out. Gas leakage or under charge Compressor motor running at less speed. Internal valves of compressor not operating efficiently. 3. Insufficient cooling may be due to - Thermostat not operating properly. System under charged with freon. Compressor motor running slow. ________________________________________________________________________ ___________________________________________________________________________ Choke in the system. Any of the stop valve closed Expansion valve choked or not opening sufficiently. Condenser fins choked Evaporator fins choked. Air filters for return air choked. Capacity control not working properly. 4. Excessive cooling may be due to - Thermostat not operating. Compressor motor failing to stop. 5.10.7 Service trouble 1. HP cut out operates due to - Malfunctioning of the cutout Condenser fan motor failure. Condenser fins and tubes dirty Any stop valve is closed or partly closed. Freon gas over charged. Air in the system. 2. LP cut out operates due to - Malfunctioning of LP cut out. Gas leakage or under charge Compressor motor running at less speed. Internal valves of compressor not operating efficiently. 3. Insufficient cooling may be due to - Thermostat not operating properly. System under charged with freon. Compressor motor running slow. Choke in the system. Any of the stop valve closed Expansion valve choked or not opening sufficiently. Condenser fins choked Evaporator fins choked. Air filters for return air choked. Capacity control not working properly. 4. Excessive cooling may be due to - Thermostat not operating. Compressor motor failing to stop. ________________________________________________________________________