Roof Mounted Air-Conditioning Package Units for Railway Coaches PDF

___________________________________________________________________________ 6. ROOF MOUNTED AIR-CONDITIONING PACKAGE UNITS FOR RAILWAY COACHES 6. BRIEF DESCRIPTION The roof-mounted AC equipment for AC coaches of Indian Railways would provide more comfortable journey an...

___________________________________________________________________________ 6. ROOF MOUNTED AIR-CONDITIONING PACKAGE UNITS FOR RAILWAY COACHES 6. BRIEF DESCRIPTION The roof-mounted AC equipment for AC coaches of Indian Railways would provide more comfortable journey and also help attach more coaches in the superfast trains like Rajdhani Expresses. These roof-mounted AC units of new design are more efficient and lightweight and are manufactured indigenously. Two high capacity packaged air-conditioning units of minimum of 7.0 TR of cooling in 45°C ambient i.e. 14.0 TR for one coach, will replace the present underframe open type AC system of capacity 5.2 TR each (Total 10.4 TR) for each coach. Two packaged units are used in one coach each mounted above the toilets on both ends supplying conditioned air into a tapered duct to serve the coach end to end. The units (two in each coach) are fitted with 4 compressors but operate under normal with 3 compressors and the 4th one acts as standby and works only during peak days of the summer. Compressors are started in sequence with time delay to reduce the peak demand of electricity during start ups. These units are thus more energy efficient and are more reliable than the existing open units and would be better in operation. The high capacity AC units of roof mounted type is a fore runner to futuristic super fast trains. This units can work on E.O.G. systems in addition to S.G. systems. The roof mounted unit needs approximately 11.5 KW, 20 ampere at normal condition. Modular type AC units for rail coaches is a major breakthrough in rail-coach technology. A modular type roof-mounted packaged AC unit for rail coaches, the first of its kind brings India abreast with the latest in the state of the art of air-conditioning technology prevalent the World over. The units are extremely energy efficient and reliable. They use two hermetically sealed compressors of half capacity in each packaged unit. These compressors are specially developed for rolling stock application under varying dynamic conditions after rigorous testing and trials before being used in the AC units. 6.1 PRESENT SYSTEM The AC coaches running on Indian Railways can be broadly divided into two categories. Self generating (S.G.) coaches. End-On-Generation (EOG) coaches. 6.1.1 Self-Generating Coaches Power supply demand for AC equipments is met from axle driven transom-mounted brushless alternator which is rated for 110 V DC supply. At low speeds and during halts the ________________________________________________________________________ ___________________________________________________________________________ power requirement is met from 110 V lead acid battery housed in battery boxes mounted on the underframe of the coach. 6.1.2 End-On-Generation Coaches AC coaches draw power from the diesel-generating sets carried in coaches put in the front and rear of the rake, functioning at 415/750 V, 3 phase, 50 Hz AC supply. The power is distributed to entire rake and thus to each coach through two sets of 3 phase 415/750 V feeders. Each coach is provided with control, distribution and feeder changeover arrangement on 415/750 V control panel. The AC equipments operate at 415 V, 3 phase, 50 Hz AC supply. The airconditioning system in both types (SG or EOG) of Indian Railways stipulates use of open type compressor, condenser, liquid receiver with dehydrator separately mounted on the underframe of the coach. The evaporator comprising cooling coils, heater elements and blower fans with motor is mounted between coach roof and false ceiling. The conditioned air is blown through the central duct and distributed inside the coach through adjustable grills diffusers. 6.1.3 Draw-backs of conventional AC system The existing system using open type compressor, poses problems such as refrigerant leakage from pipes and their joints heavy weight, large space occupation, more maintenance problems, consuming more power and thus less energy efficient. 6.2 SALIENT FEATURES OF ROOF-MOUNTED AC PACKAGE UNITS Light in weight, saves fuel for hauling. Total weight of both units is 900 Kg as compared to 2700 Kg for conventional AC unit. Saves in fuel consumption. In the Rajdhani express e.g. the total weight reduction in 20 coaches (1.8 x 20 = 36 MT) equals the weight of one coach. Therefore, one additional coach can be hauled. Keeping in view the low price and light weight, the unit pays for itself in one year operation. Low cost of installation at the coach building factory since the system is factory made, assembled, gas charged and tested for performance prior to delivery. The installation requires simply to lower the unit in the false ceiling above the toilets on both ends of the coach and connection of wiring, drain pipe and flexible duct. In case of failure, replacement of the unit with new unit can be done in less than two hours by simply lifting the defective unit by a crane and lowering the new one in place. The A.C unit remains outside the partition wall and therefore, no chance of water leakage on passengers Fresh air is taken from the roof through condenser area which gives a relatively clean air free of the smells of toilets which are common in conventional A.C. coaches. ________________________________________________________________________ ___________________________________________________________________________ Hermetically sealed system with no fittings or openings, thus it presents little potential of gas leakages and break-downs. The unit is almost maintenance free since it uses 3ph AC motors which have no commutators or brushes to wear out. Uses more environment friendly refrigerant R-22 and very small quantity less than 3 Kg. Mounted on the roof, thus dirt or dust collection in condensers is negligible and therefore, requires practically no maintenance or water spraying on condenser coils. No chance of damage due to flash floods during the monsoons. No chance of damage due to cattle run. Energy efficient - uses less electricity, saves fuel for generation. Humidity control in monsoons possible through use of micro processor - based control system. It will also provide optimum use of all equipments and even wear to compressors through rotation of operation. 6.3 COMPARISON OF ROOF-MOUNTED A.C. SYSTEM WITH CONVENTIONAL UNDERFRAME HUNG A.C. SYSTEM Sr. Roof mounted Conventional No. Description No. A.C. Unit A.C. Unit 1. Weight 900 Kg 2700 Kg 2. Installation time 4 hrs. 4 days 3. Refrigerant R-22 (CHC1F2) R-134 A 4. Refrigerant charge Less than 3.0 Kg 15 – 20 Kg. 5. System design Hermetically sealed Open 6. Ref. Leak Potential Nil Enormous 7. Maintenance Little Heavy 8, Dust collection Little Heavy 9 Damage due to cattle run Nil Heavy Sr..No. Description Roof mounted Conventional i i ________________________________________________________________________ ___________________________________________________________________________ No. A.C. Unit A.C. Unit 10. Damage due to flash Heavy Nil floods Deteriorates quickly due to dust 11. Performance Excellent collection under coach 12. Technology Latest Old and obsolete 13. Water drop on passengers Nil Some times 14. Fresh air From roof (Does not take From sides toilet smell) (Takes toilet smell) 15. Capacity control 25% to 100% 50% to 100% (4 compressors) (2 compressors) 16. Down time for repair 4 Hrs-(Replace unit) Very long (Requires repairs to be made on coach itself) 6.4. PERFORMANCE OF ROOF MOUNTED AC PACKAGE UNITS Major problems/short comings experienced by railways with roof mounted AC package units are, Gas leakage. Water ingress into corridor. Tripping of packages through safety cut-outs. Failure of AC control panel 6.4.1 Gas leakage This problem was more acute in packages of one particular make. Analysis of problem indicated that this was due to, Packages were not subjected to the vibration test. Inadequate securing of refrigerant piping. Non-securing of compressor top resulting into excessive vibration in discharge pipe. Defective packless vibration eliminator (particular lot). Other manufacturing shortcomings like longer length of charging line, unsatisfactory brazing etc. The concerned firm in consultation with RDSO and IIT, Delhi, have carried out ________________________________________________________________________ ___________________________________________________________________________ following modifications. Securing refrigerant piping properly specially at the places where vibration levels were found to be on higher side by IIT, Delhi, Securing the compressor at the top and using solid mounting pads. To replace packless vibration eliminators with U loop. To improve the general workmanship and conducting tests more rigidly. Packages with these modifications have been successfully tested for vibrations. The other make has also been tested for vibration, 6.4.2 Water ingress into corridor This problem can be classified into two categories; Problems related to rain water Problem related to condensate water. Major factors contributing to first problem were, Inadequate/ineffective drainage area Interfacing between trough and package not water tight. Package not of standard design and not water tight. Inadequate/ineffective drainage area This is considered to be the major culprit. It is felt that if it is corrected there will be considerable improvement. Drainage area has now been increased to about three times of the earlier and also made effective by taking if vertically downward from the bottom of the trough. Interfacing between trough and package not water tight In earlier design, packing provided between package and trough was getting dislodged due to sustained vibrations. Now the arrangement has been modified to have single gasket under point pressure mounting with skirting all around the opening. Package not of standard design and not water tight Water was found to be entering into the corridor through evaporator area and other structural members of the package due to not standard design and evaporator section not being water tight. This stands corrected now. Problem related to condensate water This problem can be further divided into two categories: a. Condensate water dropping into corridor. b. Condensate water carried over by blower and thrown into duct. Problem 'a' has been observed in both packages while problem ‘b’ is confined to only one make of package units. Causes of the problem as identified are, ________________________________________________________________________ ___________________________________________________________________________ Condensate water collected into drip tray not getting drained off effectively due to non provision/removal of air trap (U-trap) at the outlet of condensate drain or due to improper slope of the external drainage connections This stands corrected now. Defective drip tray design in respect of inadequate depth and covering at the top. Clogging of filters - This needs to be looked into by Railways. In the latest packages condensate drain has been taken towards condenser area and provision of U-trap is in the scope of package manufacturer. This is expected to eliminate the problem due to negative pressure of blower over drip tray getting partly neutralized by condenser and also the intact provision of U-trap. Design of drip tray has also been modified to provide maximum possible depth. It is felt that if the filters are periodically cleaned problem will not be experienced. For the existing coaches modifications have been evolved and demonstrated on three ACCNs with full trough. Modification in respect of coaches with half trough are under validation. Modifications require two inputs, a. Modification in trough. b. Modification of old packages to make them conforming to latest design. While input 'a' is to be arranged by railways on their own, for input 'b' RCF has entered into contracts with package manufacturers for which even the cost will be born by RCF. It has also been jointly decided by RDSO & RCF to try out flat roof mounting arrangement of AC package on few coaches for which drawings are to be given by RDSO. 6.4.3 Tripping of packages through safety cut-outs This problem was experienced during the peak of summer. To overcome the problem, RDSO's relevant specification has been revised specifying the satisfactory functioning of the package at an ambient of 57°C. 6.4.4 Failure of AC control panel Initially AC control panels supplied by different manufacturers were of different designs and lay-outs which were causing lot of problems. Subsequently, RCF standardized the lay-out and design of control panel to have 100% interchangeably among different makes. The procurement of panels was offloaded to industry as package manufacturer did not respond promptly enough and also due to price implications. However, in these panels, problem of coordination and poor quality of particular make of switchgear items were reported by railways. Railways have been advised to replace this particular make of items by Siemens make which can be made available by RCF. Accordingly a decision has been taken to procure the control panel from package manufacturers alongwith AC packages. Earlier, there were two types of control panels one with 110V AC control supply and other with 110V DC supply. Specification of control panel has been revised by RDSO. Now there will be only one type of control panel (with 110V AC control supply) for both SG and EOG type coaches. ________________________________________________________________________