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Heating Ventilating Air Conditioning Guide 1939 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 ^ bridge wall, the total length of the furnace may be used except that this len,,i ; is not to exceed 2H W- BOILER OUTPUT b Boiler output as defined in A.S.H.V.E. Performance Test Code f0r Steam Heating Solid Fuel Boilers (Code No. 3) is the quantity of heat 1 available at the boiler nozzle with the boiler normally insulated., ; 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 for Stoker Fired Boilers and Bituminous Coal Rated in Square Feet Steam Radiation Rating Steam Heating, Solid Fuel, Hand-Fired Boilers, the perrffocrkmmaance 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 boiler 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. 256 Chapter 13. Heating Boilers .. Horsepower: The evaporation of 34.5 lb of water per hour iMid at 81S F which is equivalent to a heat output of 970.2 X 34.5 = 33471.9 Btu per hour. F 'valent Evaporation: The amount of water a boiler would ^^ate in pounds per hour, if it received feed water at 212 F and eVaPrized'it at this same temperature and at atmospheric pressure. vaj*>- usually considered that 10 sq ft of boiler heating surface will pro,1 U a rated boiler horsepower. A rated boiler horsepower in turn dUCCcarrv a design load of from 100 to 140 sq ft of equivalent radiation. fHs apparent, therefore, that 1 sq ft of boiler heating surface can carry a i1- ]Md of from 10 to 14 sq ft of equivalent radiation, or somewhat dC^eif 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 is 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 ralorific value of 1 lb of combustible as fired. The combined efficiency of boiler, furnace dnd crate 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 in 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 on 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 Association6. 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 amount of installed radiation was determined is the sum 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, indirect 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. *A.S.H.V.E. Research Report No. 907--Study of the 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. 617). A.S.H.V.E. Research Report No. 925--A Study of intermittent Operation of Oil Burners, by L. E. Seeley and J. H. Fowere (A.S.H.V.E. Transactions. Vol. 38, 1932, p. 317). . Code f Minimum Reauirements for the Heating and Ventilation of Buildings (Edition