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Heating Ventilating Air Conditioning Guide 1938 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 hoiler will be called upon to carry. (A.S.H.V.E. Standard Code for Rating Steam Heating Solid Fuel Hand-Fired Boilers--Edition of April, 1932.) The estimated maximum load is given by: . 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 1, 2. and: 3 and the heating-up factors given in Table 3. Table 3. Warming-up Allowances for Low Pressure Steam and Hot Water Heating Boilers3! bi c_________________ Design Load (Representing Summation or Items 1,2, and 3,4 Btu 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 i,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 for 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 VentilaUon 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 Sabfn Crocker (Heating, Piping and Air Conditioning, March, 1932). oThis 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. 3). d240 Btu per square foot. . Other things to be considered are: 5. Efficiency with hard or soft coal, gas, or oil firing, as the case may be. 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 in the various spaces of the building to be heated, which reserve, however, - ' *Loc. Cit. Note 7. 252 Chapter 13. Heating Boilers is not in use at all places at the same time, or in any one place.at all times, Fpr 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 1000 000 600 TOO 600 900 400 300 FUEL CAPACITY. LB. ' FUEL AVAILABLE, LB. FUEL DEPTH,IH. 651 414 10 ASH SULPHUR MOISTURE BTU PER L8. B.B7 B-BB 3.00 13,655 Fig. 2. Typical Performance Curves for a 36-in. Cast-Iron Sectional Steam Heating Boiler, Based on the A.S.H.V.E. Code for Rating Steam Heating Solid Fuel Hand-Fired Boilers 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 100 F. For more specific information, see Chapter 43. 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 25,per cent for steam systems and 35 per cent for hot water systems is preferable to ignoring entirely the load due to heat loss from the supply 253