Document GKJw4yL64DymkL2aKe5YqKRQm

American Society of Heating and Ventilating Engineers Guide, 1936 % in. wood k = 0.8 = 0.9350 Inside air film Total = 0.6080 = 4.8296 Us = v oLa's = 0.207 Btu per hour per square foot per degree Fahrenheit. 4.8296 Window Coefficient = Uv = Btu per hour per square foot per degree Fahrenheit. Outside air film yg in. glass k = 1.13 1/k = 0.286 = 0.889 iy in. ait space ) in. glass Inside air film a = 1.06 1/a. = 0.940 = 0.889 = 0.608 Total = 3.612 /w = = 0.278 Btu per hour per square foot per degree Fahrenheit. o.OIa Floor Coefficient = U{ -- Btu per hour per square foot per degree Fahrenheit. Outside air film Hs in- steel in- air space 1 in. hairfelt Ms in. steel 1 in. composition Inside air film a = 1.2 k = 0.25 * =6 1 /a = 1/1.2 1/k 1/k = 0.2860 = 0.0002 = 0.8320 = 4.0000 = 0.0002 = 0.1666 = 0.608Q Total = 5.8930 Ui = . = 0.170 Btu per hour per square foot per- degree Fahrenheit. ; . . 5.893 Heat Leakage: Through roof = 880 X 0.232 = 204 side walls = 865 X 0.207 = 180 floor = 687 X 0.170 =. 117 windows = 190 X 0.278 = 53 end walls = 147 X 0.207 = 31- 585 Btu per hour per degree Fahrenheit. Total heat gain = 585 ,(<o -- t) = 585 X 15 = 8775 Btu per hour. Sensible heat gain froiti make-up air = Q X 60 X d X Cp X (to -- t) = 500 X 60 X 0.07356 X 0.241 X 15 = 7950 Btu per hour. Latent heat gain from outside air = Z.X60XQXdX^f = 1060 X 60 X 500 X 0.07356 X 0.00314 = 7350 Btu per hour. Heat gain from passengers = (68 X 400) + (1 X 650) = 27:850 Btu per hour. Heat gain from evaporator motor = X 0.746 X 3415 = 1960 Btu per hour. Heat gain from solar radiation: ' Heat gain through roof = Ut X At X 40 = 0.232 X 880 X 40 = 8150 Btu per hour. Heat gain through side wall = 0.207 X 433 X 25 = 2230 Btu per hour. 262 Chapter 13--Railway Air Conditioning 190 Heat gain through window = 0.7 X X 60 = 4000 Btu per hour. Total heat gain from solar radiation Summary of Total Heat Gains: Leakage Sensible heat from outside air Latent heat from outside air Heat from passengers Heat from evaporator fan motors Solar radiation = 14380 Btu per hour. 8,775 7,950 7,350 27,850 1,960 14,380 Total 68,265 Btu per hour. This would require a refrigerating capacity of 12'qqq = 5.7 tons. HUMIDITY CONTROL The temperature to be maintained in a car depends upon the outside temperature and the desired humidity inside the car. With a low hu midity it is necessary to maintain a higher temperature to establish a desirable comfort condition. Little humidity control has been attempted on cars up to the present time. A certain degree of automatic humidity control is secured with cooling, but the relative humidity obtained depends largely on the temperature of the evaporator, which should be below the dew point temperature of the air. With certain outside atmospheric conditions it may not be possible to operate the conventional equipment with a sufficiently low evaporator temperature to reduce the humidity without dropping the temperature too low. One method has been developed whereby the evaporator temperature is carried below the dew point a sufficient amount to insure dehumidification and then the.cold air is heated to the proper temperature by passing it over coils through which part of the high temperature liquid from the compressor is bypassed. During the heating season humidification is desirable from a. comfort standpoint, but the proper amount of humidification required would doubtless cause the windows to become frosted. A steam or water spray controlled.by a humidistat will provide the necessary moisture if humidi fication is desired. TEMPERATURE CONTROL .The control of the air conditioning equipment should be simple but at, the same time as nearly automatic as possible. The use of a centralized, control panel for all control switches, fuses, relay, etc., will simplify the installation and operation. Generally, separate thermostats are used for heating and cooling control. The best location for the thermostats depend upon the car layout and method of air distribution and can best be determined for any particular type of car and equipment, by. careful consideration of the several factors involved. The floor heat thermostats are usually located near the floor. The overhead heat and cooling ther mostats are placed in the upper part of the car, sometimes in the air ducts. All thermostats should, be located so that the air can circulate freely around them. Maintenance of uniform comfort conditions for cooling, 263