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American Society of Heating and Ventilating Engineers Guide, 1936 Based on an average cost of coal, water and locomotive lubrication of $0.001133 per pound of fuel burned and the following assumptions: generator and drive efficiency 80 per cent, locomotive mechanical ef ficiency (cylinders to tender drawbar) 90 per cent, 3.5 lb coal per cylinder horsepower and 6 lb of water per pound of coal, the cost of generating 1 kw of electrical energy would be $0.00738, and 100 lb of steam $0.01888. This is based on the assumption that the cost of coal, water and loco motive lubrication would increase in direct proportion to the amount of coal burned. As the cost of locomotive lubrication would not increase in direct proportion to the amount of coal burned, the extra cost of lubri cation included in the figure should offset the increase in cost of loco motive maintenance due to the additional load. Using an average capa- Fig. 2. Costs Railway Passenger Car Air Conditioning city of 3.3 tons, the cost per hour of operation would be approximately $0.04 for steam and mechanical compressor systems and $0.55 for ice, using a price of $4.00 per ton for ice. These figures are based on the assumption that the motor driven com pressor is receiving power direct frorri the generator and that the efficiency of the direct drive is the same as the combined efficiency of the axle generator, drive, and motor. Of course part of the current for the \ electric drive would be taken from the battery and therefore the battery C efficiency would, have to be taken into consideration. Likewise the lower efficiency should be considered of the direct drive at the higher speeds and it would be necessary to know the characteristics of the run under con sideration to make an exact comparison. '> For a given run the total kilowatt hours required for the electro mechanical; system would ~ _ EgXlgXTg Eb X lb X Tb *, . " 1000 + eb X 1000 ' where Eg = voltage with generator cut in. Eb = voltage with generator cut out. 1 - 266 | _____' Chapter 13--Railway Air Conditioning /g = current with generator cut in. /b = current with generator cut out. Tg = time generator cut in. 7b = time generator cut out. ,eb = battery efficiency. _ ,, . kilowatt hours X 1000 Cylinder horsepower hour = gg X ed X et X 746 where eg -- generator efficiency. c& = drive efficiency. Ci = locomotive mechanical efficiency. With these formulae and the coal and water rates of the locomotive the total amount of fuel and water required to supply the power enroute can be calculated. Fig. 2 shows the relation between the cost per thousand car miles and total miles run per year for the ice and electro-mechanical systems. These curves are based on the cost figures previously given and the follow ing formula: where c-ost per rnousana car miles CM XD 45 A = Annual fixed charges (dollars) calculated as follows: a. Depreciation b. Interest e. Taxes and insurance 12.5 per cent 6.0 per cent 1.5 per cent Total CM = thousand car-miles per day. D = days in service per year. M -- maintenance cost per thousand car miles. C = operating cost per hour. 45 = average miles per hour. 20.0 per cent No charges for precooling are included. The curves for the steam and direct drive mechanical compressor systems would be between those shown for the ice and electro-mechanical compressor systems. PROBLEMS IN PRACTICE 1 What is the capacity of the air conditioning unit in the average car? 2000 to 2500 cfm. 2 How much steam is required for car heating on the coldest days? ' Pullmans 250 lb per hour, coaches 150 to 175 lb per hour, baggage cars 150 lb per hour. 3 What types of cooling systems are used? Ice, steam jet, and mechanical compressor systems. 267