Document NE2JGKbmzbMqEEZaD7rVxa6rw

Heating Ventilating Air Conditioning Guide 1938 W = average width of furnace, measured at the bottom of the fuel bed, feet. L = length of furnace, feet. If the furnace is longer than the fuel bed or contains a bridge wall, the total length of the furnace may be used except that this length is not to exceed 2J^ W. BOILER OUTPUT Boiler output as defined in A.S.H.V.E. Performance Test Code for Steam Heating Solid Fuel Boilers (Code No. 3) is the quantity of heat available at the boiler nozzle with the boiler normally insulated. It should be based on actual tests conducted in accordance with this code. This output is usually stated in Btu and in square feet of equivalent heat ing surface (radiation). According to the A.S.H.V.E. Standard Code for Fig. 1. Furnace Heights foe Stoker Fired Boilers and Bituminous Coal Rated in Square Feet Steam Radiation . *\ Rating Steam Heating, Solid Fuel, Hand-Fired Boilers, the performance data should be given in tabular or curve form on the following items for at least five outputs ranging from maximum down to 35 per cent of maxi mum: (1) fuel available, (2) combustion-rate, (3) efficiency, (4) draft tension, (5) flue gas temperature. The only definite restriction placed on setting the maximum output is that priming shall not exceed 2 per cent. These curves provide complete data regarding the performance of the boiler under test conditions. Certain other pertinent information, such as grate area, heating surface and chimney dimensions is desirable also in forming an opinion of how the boiier will perform in actual service. The output of large heating boilers is frequently stated in terms of boiler horsepower instead of in Btu per hour or square feet of equivalent radiation. . 250 Chapter 13. Heating Boilers Boiler Horsepower: The evaporation of 34.5 lb of water per hour from and at 212 F which is equivalent to a heat output of 970.2 X 34.5 == 33,471.9 Btu per hour. . Equivalent Evaporation: The amount of water a boiler -would evaporate, in pounds per hour, if it received feed water at 212 F.and vaporized it at this same temperature and at atmospheric pressure.' It is usually considered that 10 sq ft of boiler heating surface will pro^duce a rated boiler horsepower. A rated boiler horsepower in turn can carry a design load of from TOO to 140 sq ft of equivalent radiation. Itis apparent, therefore, that 1 sq ft of boiler heating surface can carry a design load of from 10 to 14 sq ft of equivalent radiation, or somewhat more if the boiler is forced above rating. The application of these values is discussed under the heading Selection of Boilers.' BOILER EFFICIENCY . The term efficiency as. used, for guarantees .of ..boiler performance Js usually construed as follows: 1. Solid Fuels. The efficiency of the boiler alone is the ratio of the heat absorbed by the water and steam in the boiler per pound of combustible burned on the grate to the calorific-value of 1 lb of combustible as fired. The combined efficiency of boiler, furnace and grate is the ratio of the heat absorbed by the water and steam in the boiler, per pound of fuel;as fired to the calorific value of 1 lb of fuel as fired. 2. Liquid Fuels; The combined efficiency: of. boiler, furnace and burner is the ratio of the heat absorbed by the water and steam iri: the boiler per pound of fuel to the calorific value of 1 lb of. fuel. . Solid- fuel boilers usually show an efficiency of 50: to 75 per cent when , operated under favorable conditions at their rated capacities. Infor mation bn the combined efficiencies of boiler, furnace and burner has resulted from research conducted at Yale University in cooperation with the A.S.H.V.E. Research Laboratory -and the American Oil Burner Association*.. SELECTION OF BOILERS Estimated Design. Load: The load, stated in Btu per hour or equiva lent direct radiation, as estimated by the purchaser for the conditions of inside and outside temperature for which the aniount of installed radiation was determined is the siim of the heat emission of the radiation to be actually installed plus the allowance for the heat loss of the connecting piping plus the heat requirement for any apparatus requiring heat con nected with the system (A.S.H.V.E. Standard Code for Rating Steam Heating Solid Fuel Hand-Fired Boilers--Edition of April, 1932). The estimated design load is the sum of the following three items7: 1. The estimated heat emission in Btu per hour of the connected radiation (direct, indira:t or central fan) to be installed. . ., 2. The estimated maximum heat in Btu per hour required to supply water heaters or other apparatus to be connected to the boiler. 'Study of Che Characteristics of Oil Burners and Heating Boilers, by L. E. Seeley and E. J. Tavanlar (A:S.H.V.E..Transactions, Vol. 37,1931, p. 517), A Study of Intermittent Operation of Oil Burners by L. E. Seeley and J. H. Powers (A.S.H.V.E. Transactions, VoLJJ8>J32, p. 317). 'A.S.H.V.E.' Code of Minimum Requirements for the Heating and Ventilation of Buildings (Edition of 1929). 251