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662 . Chapter 37 1945 Guide i' loads make the problems of air distribution and air delivery in railway cars critical. Various methods may be used to distribute the air delivered to the interior of the. car by the circulating fan or blower.^ The methods com monly used are: 1. A duct lengthwise along the center of the car. 2. One or two side ducts built on the outside of monitor-roofed cars, or on the inside of-turtle-backed or arch-roofed cars. 3. A ceiling which is perforated for the emission of air into the car; the air being carried to the ceiling by an overhead duct. From one-half to the full area of the ceiling is used for the distribution of the air although practical considerations generally limit the available area to about two-thirds. As large a part of.the ceiling area as possible should be used for air distribution. Delivery grilles and plaques are used, and are often designed to give considerable entrainment and mixing to avoid cool drafts. Smoking rooms present a special problem. The cloud of smoke that usually hangs near the ceiling can be broken up by having the incoming air directed along the ceiling in all directions at a velocity somewhat higher than that used for the rest of the car. The air should be exhausted from the room by a fan or through a grille to the washroom or lavatory, and then outside by a fan in a ventilator. For compartinents an adjustable supply duct outlet grille of suitable size and design should be provided and provisions made in the door or partition for the removal of the air to be recirculated. Lower berths in sleeping cars and office cars should be provided with an , adjustable air outlet which will discharge the amount of air desired at low velocity in any direction so that the occupant can regulate the ventilation to meet his own requirements. - In cars containing but one or two rooms or compartments, satisfactory results may be Obtained by discharging the air directly from the con ditioning unit into the upper part of the car. Care must be taken to have a proper discharge velocity. If the velocity is too low, the air will drop before reaching the end of the car and if too high it will discharge against the end bulkhead and be reflected back. Care must be exercised to secure proper circulation, otherwise objectionable drafts will be experienced. The recirculating air grilles are usually of the straight flow type, and should be located so that objectionable drafts will not be created by the return air. The outside air intakes, located in the car vestibule, on the side of the car, or on the roof of the car, depending upon the location of the cooling coils, should be of ample size to permit the entrance of suf ficient outside air. On many of the recently air-conditioned cars, there are no dampers or shutters at the outside air intakes, the percentage of outside air being controlled by adjusting the flow through the recircu lating grille. Air Cleaning AH of the air circulated by the blower is filtered before passing over the cooling coils. In some cars the. outside and recirculated air is filtered separately before mixing, while in others the air from the two sources is mixed before passing through a common filter. Filters in use are made of metal, wool, cloth, spun glass, hemp, paper, hair, and wire screen. Most filters have a viscous coating of oil for greater cleaning efficiency. Some types may be cleaned, retreated, and returned to service while other types are discarded when dirty. Transportation Air Conditioning____________________ ,____________ RAILWAY PASSENGER CAR WINTER AIR CONDITIONING The majority of cars in service use steam from the locomotive or from ahead-end, oil-fired boiler as a source of energy fox winter heating. In some instances electrical energy from either a head-end generating set or motive power supply is utilized for resistance heating. In still Other cases electrical energy and waste heat from individual car engine-generator sets are employed. The peak heating loads which depend largely uponthe amount of insulation used in the car, the type of windows (whether single or double glazed), and the ventilation rate, may vairy from 150,000 to 250,000 Btu per hour. In order to temper the cold outside air, about 30 to 50 per cent of the total heat energy required is distributed by means of finned coils or resistance heaters located in the outside air duct. The remainder is - usually transmitted to the car air by finned tubing located along the sides of the car near the floor, thus preventing cold convection currents falling from the car windows from reaching the feet of the passengers. RAILWAY PASSENGER CAR SUMMER AIR CONDITIONING Three general types of cooling or refrigerating, equipment are being used in 13,362 (May, 1944) air conditioned railway cars and 31 air conditioned rail motor cars in the United States. Of these, 30 per cent are ice activated, 15 per cent use steam jet systems, and 50 per cent employ mechanical compression schemes. These systems which func tionally are identical with those used for stationary applications (see Chapter 24) are modified in design to meet the requirements of mobile service. Contrasted with stationary applications of summer conditioning equipment, the use of water as a final means of heat disposal from con densers cannot be resorted to because water in such quantities cannot be transported economically. Accordingly, air cooled or evaporative con densers are always used, with the result that mobile cooling equipments operate at higher temperature, pressure, and power requirement levels , than stationary equipment. The maximum cooling and dehumidifying load which depends largely upon the amount of insulation, the type of windows, the ventilation rate, the sun intensity, and the number of passengers may vary from 60,000 to 96,000 Btu per hour. An average ice-activated system for such capacities uses about 500 lb of ice and 1.2 kw per hour. The increase in car weight due to such a system is approximately 8500 lb. The same service from a steam jet system is obtained with the expendi ture of 180 lb of steam and 3.3 kw per hour, with an added weight oer car of 8000 lb. The mechanical compression systems, all of which use dichlorodifluoromethane as a refrigerant, may be classified by several types depending on the method of driving the compressor. The source of power for driving the compressor (approximately 10 hp) is complicated by the necessity of obtaining this power at all times whether the car is in motion or standing still on the right-of-way or in a terminal where auxiliary power plug-ins are available. In those cases where compressors are driven from car axles, additional refinements in the drive are necessary in order that a nearly constant cooling capacity may be obtained from a variable speed power source. Numerous combinations of electrical generating schemes for generating sufficient electrical energy from the car axle for lighting, ventilation, and summer air conditioning are in use, and their operation