Document mB2Z4mK0Lxq7gp2yVewgnJ1zZ

.American Society of Heating and Ventilating Engineers Guide, 1930 1. The estimated heat emission in B.t.u. per hour of the connected radiation (direct, indirect or blast) to be installed, as previously determined by calculations given in Chapter 2 of The Guide. 2. The estimated maximum heat in B.t.u. per hour required to supply water heaters or other apparatus to be connected to the boiler. 3. The estimated heat emission in' B.t.u. per hour of the piping connecting the radiation and other apparatus to the boiler. 4. The estimated increase in the normal load in B.t.u. per hour due to starting up cold radiation, etc. This percentage of increase to be based on the sum of items (1), (2) and (3) shall not be assumed less than the following: Sum of (1), (2) and (3): Up to 100,000 B.t.u. add 65 per cent. 100.000 to 200,000 B.t.u. add 60 per cent. 200.000 to 600,000 B.t.u. add 55 per cent. 600.000 to 1,200,000 B.t.u. add 50 per cent. 1,200,000 to 1,800,000 B.t.u. add 45 per cent. Above 1,800,000 B.t.u. add 40 per cent. Other things to be considered are: 5. The kind and amount of attention available. Attention is least skillful and least frequent for owner-operated residence installations and generally increases in skill as well as frequency as size of boiler increases. Local fuels and types of firing service must be considered carefully in this connection. 6. The kind of fuel to be used, including size and characteristics. 7. Size arid height of the available chimney. With definite requirements as given by items 1 to 4 available, the boiler performance information, obtained according to American Society of Heating and Ventilating Engineers Code No. 3--Performance Test Code for Steam Heating Solid Fuel Boilers, can be used for selection of the proper size of solid fuel burning boiler. Other Factors in Selection of Boiler As it will usually be found that several boilers will meet the specifica tions, the final selection of the boiler will be effected by other considera tion? as follows: (a) Dimensions of boiler; (6) Height of water line; (c) Durability under service; (d) Convenience in firing and cleaning; (e) Type of controls; (f) Adaptability to changes in fuel arid kind of attention; (g) The output required during the greater part of the season. In large installations the use of several smaller boiler units instead of one larger one will obtain greater flexibility and economy by permitting the operation of a required number of units according to heat require ments at the best operating efficiency. Numerical Value of Maximum Hourly Output Experience with gas-fired boilers, which are rated on B.t.u. output and which can only slightly exceed the rated output, but which require no chimney draft, has shown that a continuous output capacity of 25 per cent in excess of the normal heat loss of radiation, plus piping, is ample for all direct radiator installations. This corresponds to an output of 40 to 60 per cent in excess of the normal heat loss of the radiation, depending upon the proportion of piping to radiation. Gas-fired boilers rated according to the American Gas Association 264 Chapter 15--Boilers for Steam and Hot Water Heating method and having, therefore, A.G.A: Ratings are selected in the majority of direct radiator installations, according to the table of selection factors given in Chapter 11, page 229. Upon the basis of gas-fired boiler experience, a coal-fired boiler which could deliver a continuous average output of 25 per cent in excess of radiation and piping would be amply large for any job. This is true for an oil-fired boiler, provided the known output of the combination of boiler, burner, and chimney is used. Where test data are not available for the contemplated combination of boiler and oil burner, economical performance may be obtained by selecting a boiler in which the heat absorbed per square foot of boiler heating surface at the maximum continuous output is approximately 4,000 B.t.u. per hour. It should be ascertained that the burner selected has sufficient combustion space to permit the burning of the required quantity of the available oil fuel. In the case of coal-fired boilers, however, it is necessary to make addi tional allowance for the following conditions not due to boiler construc tion which may obtain at the time when the maximum pick-up load occurs, (a) insufficient draft; (b) poor quality of fuel; (c) fuel bed not in ;good condition; (d) inferior quality of attention; (e) necessity of firing a charge of fuel that will last for a long period; (/) dirty flues. The conditions (a) to (/) inclusive, reduce the output obtainable to a point below that which could be obtained under good or normal conditions and necessitate a larger boiler, in order that when the normal output is decreased by the effect of items (c) to (/) there will still be available a quantity of heat 25 per cent in excess of the radiation-plus-piping loss. Coal-fired boilers, therefore, are usually selected with a maximum con tinuous output 60 to 80 per cent in excess of the demand of radiationplus-piping. For large boiler installations the foregoing percentages in excess of the heat loss of radiation-plus-piping may be reduced to the following: Per Cent School buildings without recirculation of air.............................................. -..............50 School buildings with full recirculation of air.............. ......................................-........ 25 Buildings with periodical heating only......... -................................. :............................... 50 Other large buildings.................................................... -.............. :............... ........ .--.......... 25 For any boiler selected it is well to determine whether the rate of com bustion (fuel burned per square foot of grate per hour) will be required continuously for more than a few hours and whether it is low enough to prevent clinker trouble. With natural draft it is recommended that for continuous output (under favorable conditions), with a minimum of attention, the combustion rates given in Table 1 be not exceeded. In the case of boilers having larger grates, better draft and more frequent attention, rates of combustion may be greatly increased over those shown in Table 1. Selection of Steel Boilers Manufacturers of steel heating boilers '(members of the American Boiler Manufacturers' Association) prefer the following method of selec tion : Select a boiler with published rating (rating determined by heating 265