Document ykO8OYXxyg4mgdjrm4yaw764D

HEATINC VENTILATING AIR CONDITIONING GUIDE 1940 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 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 and Gaseous 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 or cubic foot of fuel to the calorific value of 1 lb or cubic foot of fuel respectively. 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 equivalent 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 connected with the system. 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. 3. The estimated heat emission in Btu per hour of the piping connecting the radiation and other apparatus to the boiler. Estimated Maximum Load: Construed to mean the load stated- in Btu per hour or the equivalent direct radiation that has been estimated by the purchaser to be the greatest or maximum load that the boiler will be called upon to carry. The estimated maximum load is given by8: 4. The estimated increase in the normal load in Btu per hour due to starting up cold radiation. This percentage of increase is to be based on the sum of Items.-l, 2 and 3 and the heating-up factors given in Table 3. Other things to be considered are: 5. Efficiency with hard or soft coal, gas, or oil firing, as the case may be. Boilers, . Research ------------------------------- ... . . Powers (A.S.H.V.E. Transactions, Vol. 38, 1932, p. 317). *A S H.V E. Code of Minimum Requirements for the Heating and Ventilation of Buildings (Edition of 1929). *Loc. Cit, Note 7. 246 CHAPTER 13. HEATING BOILERS 6. Grate Area with hand-fired coal, or fuel burning rate with stokers, oil, or gas. 7. Combustion space in the furnace. 8. Type of heat liberation, whether continuous or intermittent, or a combination of both. 9. Miscellaneous items consisting of draft available, character of attendance, pos sibility of future extension, possibility of breakdown and headroom in the boiler room. Radiation Load The connected radiation (Item 1) is determined by calculating the heat losses in accordance with data given in Chapters 5, 6 and 7, and dividing by 240 to change to square feet of equivalent radiation as explained in Chapter 14. For hot water, the emission commonly used is 150 Btu per square foot, but the actual emission depends on the temperature of the medium in the heating units and of the surrounding air. (See Chapter 14.) Although it is customary to use the actual connected load in equivalent square feet of radiation for selecting the size of boiler, this connected load usually represents a reserve in heating capacity to provide for infiltration Table 3. Warming-up Allowances for Low Pressure Steam and ________________ Hot Water Heating Boilers3. b. c Design Load (Representing Summation or Items 1,2, and 3,d Bta per Hour Equivalent Square Feet of Radiation^ Up to 100,000 100,000 to 200,000 200,000 to 600,000 600,000 to 1,200,000 1,200,000 to 1,800,000 Above 1,800,000 Up to 420 420 to 840 840 to 2500 2500 to 5000 5000 to 7500 Above 7500 Percentage Capacity to Add tor Warming Up 65 60 55 50 45 40 This table is taken from the A.S.H.V.E. Code of Minimum Requirements for the Heating and Venti lation of Buildings, except that the second column has been added for convenience in interpreting the design load in terms of equivalent square feet of radiation. bSee also Time Analysis in Starting Heating Apparatus, by Ralph C. Taggert (A.S.H.V.E. Transac tions. Vol. 19,1913, p._292); Report of A.S.H.V.E. Continuing Committee on Codes for Testing and Rating Steam Heating Solid Fuel Boilers (A.S.H.V.E. Transactions. Vol. 36. 1930, p. 35): Selecting the Right Size Heating Boiler, by Sabin Crocker (Seating, Piping and Air Conditioning, March, 1932). This table refers to hand-fired, solid fuel boilers, A factor of 20 per cent over design load is adequate when automatically-fired fuels are used (see Fig. 1). <1240 Btu per square foot. in the various spaces of the building to be heated, which reserve, however, is not in use at all places at the same time, or in any one place at all times! For a further discussion of this subject see Chapter 6. Hot Water Supply Load When the hot water supply (Item 2) is heated by the building heating boiler, this load must be taken into consideration in sizing the boiler. The allowance to be made will depend on the amount of water heated and its temperature rise. A good approximation is to add 4 sq ft of equivalent radiation for each gallon of water heated per hour through a temperature range of TOO F. For more specific information, see Chapter 44. Piping Tax (Item 3) It is common practice to add a flat percentage allowance to the equivalent connected radiation to provide for the heat loss from bare and covered pipe in the supply and return lines. The use of a flat allowance of