Document XR6dazMYxp0m80Qw7gB76ZX0w

Heating Ventilating Air Conditioning Guide 1938 3 If 20 tons of coal having a calorific value of 13,000 Btu per pound are burned In a warm air furnace and produce 286,000,000 Btu at the bonnet, what is the efficiency of the furnace? ___________________Number of Btu at bonnet = efficiency.. ' Number of tons X calorific value X number of pounds in one ton 286,000,000 X 100 = 55 per cent. 20 X 13,000 X 2000 4 # Make a rough approximation of the gas required to heat a building located in Chicago, 111., assuming that the calculated heating surface requirements are 1000 sq ft of hot water radiation based on design temperatures of 0 F and 70 F. Chicago has 800-Btu mixed gas, and 6315 degree-days. Using Fig. 3, the fuel consumption for a design temperature of 0 F with 800-Btu gas is found to be 0.08 cu ft of gas per degree-day per square foot of hot water radiation. 0.08 X 6315 X 1000 = 505,200 cu ft. 5 A certain building has a maximum heat loss of 250,000 Btu per hour in --15 F weather. How many tons of fuel will be required to maintain a temperature of 70 F during a 260-day heating season in which the average temperature is 39 F? The heating value of the fuel is 13,200 Btu per pound and the efficiency of com bustion is 60 per cent. 250,000 (70 - 39) 260 X 24 = g (70 + 15) 13,200 X 0.60 X 2000 6 Which item may be determined more closely, the heating value of a fuel or the efficiency of its combustion? The. heating .values of oil, gas, and solid fuels are closely determinable, whereas the efficiency of burning depends on the particular equipment chosen and the skill used in handling it. 7 In an office buildhiig, the thermostats are set to maintain 70 F from 7 a.m. to 5 p.m. and 50 F during the rest of the time. When the outside temperature is 30 F, how much saving might be expected because the temperatures are lowered? Under the above conditions the building becomes 50 F by 11 p.m. and warms up to 70 F by 8 a.m. A temperature of 70 F is maintained during 9 hours, and one of 50 F during 8 hours; the temperature would average about 60 F during the 7 hours required for cooling down and warming up. The average is 60.4 for the 24 hours. (The average temperature calcu lated would have been 58.3 F, had the warming and cooling periods been neglected.) The saving is (^=-^) x 100 = -^ X 100 = 24 per cent. ^ - . ' . U ' & How does the heat capacity of a structure influence the saving made by carrying lower temperatures during.the night? The heat storage capacity of the walls prevents rapid dropingof temperatures at night time and delays the warming up process in the morning. In an extreme case, the building would not reach the lowered temperature by the time the higher temperature is called for in the morning. But under any conditions,' the saving made by lowering the tem perature can be correctly estimated by using the average temperature observed over the 24-hour period as a factor, as in Question 7. ' What are some of the miscellaneous factors that may cause actual fuel <nsumptioh to vary from the theoretical fuel requirements as calculated by the use of heat losses, temperature difference, and fuel burning efficiency? The opening of windows; abnormally high or low inside temperatures;,other sources of beat, such as.machinery or lights; sun effect; high-occupancy; and unusual winds. 242 Chapter. 13 HEATING BOILERS Cast-Iron Boilers, Steel Boilers, Special Heating Boilers, . Gas-Fired Boilers, Hot Water Supply Boilers, Furnace Design, Heating Surface, Testing and Rating Codes, Output Effic iency, Selection of Boilers, Connections and Fittings, Erection,' Operation and Maintenance, Boiler Insulation STEAM and hot water boilers for low pressure heating work are built in a wide variety of types, many of which are illustrated in the Catalog Data Section, and are classified as (1) cast-iron sectional, (2) steel fire tube, (3) steel water tube, and (4) special. 1 ... CAST-IRON BOILERS Cast-iron boilers may be of rohnd pattern with circular grate and hori zontal pancake sections joined by push nipples and tie rods, or of rec tangular pattern with vertical sections; -The latter type may be-either of outside header construction where each section is independent of the other and the water and steam connections are made externally, through these headers, or assembled with push nipples and tie rods, in which'case the water and steam connections are internal. Cast-iron boilers usually are shipped knocked down to facilitate hand ling at the place of installation where assembly is made. One of the chief advantages of cast-iron boilers is that; the separate sections can be taken into or out of basements and other places more or less inaccessible after the building is constructed. This feature is of importance in making repairs to or replacing a damaged or worn-out boiler and should be given consideration in the original selection. -Sufficient space should be -pro. vided in. the boiler room for assembling the boiler and for disassembling it conveniently if repairs are needed. With the outside header type of boiler a. damaged section in the middle of the boiler can be removed without disturbing the other sections so side clearance should be provided. Capacities of cast-iron boilers range from that required for- small residences up to about 18,000 sq ft of steam radiation. For larger loads, cast-iron boilers must be installed in multiple, or a steel boiler, must be used.. In most cases cast-iron boilers are limited to working pressures of 15 lb for steam and 30 lb for water. Special types are built for hot water supply which will withstand higher, local water pressures. STEEL BOILERS Two general classifications may be applied to steel boilers: first, with regard to the relative position of water and hot gases,distinguished`asfife tube or water tube; second, with regard to arrangement of furnace find 243