Document 8R068qJNba3BVozD2g7Y4VnXa

1094 CHAPTER 48 1956 Guide Transportation Air Conditioning 1095 PASSENGER BUS AIR CONDITIONING quire about 5000 cfm of outdoor air, and this is provided by either centrif The passenger bus designed for urban transportation operation presents a greater problem to the designer of heating systems than does the inter- ugal or propeller type fans belted or direct-driven by the air conditioning engine. Preventing noise and vibration from affecting passengers is of vital urban bus. More frequent stops, and rapidly changing passenger load create this problem on urban vehicles. Provision of heat for the driver independent of the passenger heating system, is a further problem. The importance.. Installations must be made for quick daily engine servicing. In all cases fuel is obtained from the main bus tanks, and in some, the main engine cooling system cools the air conditioning engine. inter-urban bus, however, is usually a deluxe vehicle and may require a comfort cooling system. Space and weight limitations and vibration must Control be considered. ' Automatic temperature control is.receiving more attention in the design Heating of new vehicles.. Some municipalities and states, have enacted laws re quiring that buses operated on their streets and roads be so equipped. Recent designs of bus heating systems obtain improved air distribution. The simplest control systems for heating of urban buses consist of a single Heat in the engine coolant liquid is used to warm air by means of suitable finned coils and this heated air is distributed throughout the passenger thermostat to start and stop the blower of the heater unit. Improved heating systems employ a thermostat to control liquid flow to the heater space by ducts and outlets directed toward the floor. Some designs include cores by means of modulating valves, in combination with a means of stop finned surface near the floor in an application similar to that in railway- ping the heating blower when no heat is required. Heating and ventilating passenger cars. Forced air circulation over this finned floor heating surface control is accomplished by controlling the volume of outside air, over and has been provided to increase its effectiveness. Oil burning booster heaters above the minimum required in accordance with the temperature in the have been applied to many Diesel-powered buses to raise the temperature passenger space, by means of automatic modulating dampers in the out Nii> of the engine coolant for maximum engine operating efficiency, and to side air intake, or by-varying the speed of the ventilating air blowers. provide sufficient heat for the passenger space. In a large proportion of inter-city buses equipped with mechanical re frigeration, a single thermostat is used to start and stop the cooling opera Ventilation tion. This may be accomplished by automatically starting an engine- Shi` Air for ventilation is usually brought into a bus at the front, and dis tributed throughout the length of the passenger space by a duct or ducts driven compressor on the cooling demand or by engaging a clutch to drive the compressor. Modulated or graduated control of engine-driven com .i * ' ij near the ceiling. Except for a few designs employing 100 percent outside air for heating, no heating of the ventilating air has been provided. One recently designed distribution system for an inter-urban bus provides for a fixed minimum of outside air, and is arranged to increase the percentage of outside air to 100 percent when the heating or cooling load diminishes. pressors may be accomplished by automatic regulation of the engine throttle controlled from a thermostat in the passenger space. Complete control systems are available to coordinate operation Of the heating, ventilating and cooling equipment from a single thermostat, with automatic-changeover from heating to ventilating to cooling. ' ***$ The distribution ducts and diversion damper arrangement of this system make available two supply ducts and one return duct for heating and for AUTOMOBILE SUMMER AIR CONDITIONING cooling, with a changeover to all three ducts to supply air during the inter mediate ventilating cycle. This system permits utilization of atmospheric cooling and ventilation to the greatest degree when it can be most econom ically employed in the interval between the heating and cooling demand. The first attempts to cool automobiles mechanically were made in south western United States 1930-1940 with systems assembled from commercial components. Between 1939 and 1942 one car manufacturer built about 1500 cars equipped with a mechanical system. Customer acceptance was Conventional throw-away type filters or renewable filters are used in mixed .and the project was dropped to be reactivated again in 1953. In ,i intake air ducts for many vehicles. Electrostatic filtershave been success fully used in some installations. The need for elimination of dirt is great, 1952 the major automobile manufacturers decided that time was ripe to offer summer comfort cooling in their higher priced cars. The 1953 models but the problem is complicated by space limitations and limited power. were introduced and well accepted. In 1953 and 1954 about 125,000 units Refrigeration were sold. In 1955 some of the lower priced cars were available with summer cooling systems. Summer conditioning systems for inter-urban vehicles range in cooling capacity from 36,000 to 48,000 Btu per hour. Mechanical compression systems using refrigerants are used, and are powered by water-cooled gasoline engines of approximately 14 hp. Complete systems add from 800 to 1300 lb to weight of the coach. Some-, times an auxiliary generator driven by the refrigeration system engine is used and serves to help charge the bus battery, thereby offsetting power drain imposed by the ventilating blower. Belted reciprocating compressors and direct-driven V-type and rotary compressors are used, with engine speeds up to about 1800 rpm. Air-cooled condensers for this service re- The basic components used are fundamentally the same as in any station ary air conditioning system using the vapor compression cycle. The en gineering problem is to design for automobile application in which case the source of power is always a major obstacle to overcome. The best solution to date for automobile applications is to operate the condensing unit by -belt drive from the car motor and then control the variable refrigerating capac ity caused by the variable car motor speed by suitable means. One to seven or more horsepower are required. Compressors must be capable of operating at speeds of 4000 to 5000 rpm to last in this service. Refrigeration capacity required is about 1J to lj tons. Radiant heat, as well as high conduction heat gain due to single-glazed large glass areas, and