Document 91N1ZeoL4yY2NjBq0zypKO2LV

230 Chapter 12 1945 Guide Table 1. Steel Heating Boiler Standard Ratings Hand-Fieed Rating MeCHANICAIA/T-FiBED RATING . Catalog - Steam Water Radiation Radiation Sq Ft Sq Ft Net Load Btu per. Hoar in Thou sands Steam Radiation Sq Ft Heating Surface Sq Ft Grate Area Sq Ft Steam Radiation Sq Ft Catalog Net Load Furnace Vol ume, Oil, Gas Water Btu per Steam or Bituminous Radiation . Hoar in Radiation Coal Cu Ft Sq Ft Thousands Sq Ft 1,800 2,880 2,200 3,520 2,600 4,160 3,000. 4,800 -3,500 5,600 4,000 6,400 4,500 .7,200 5,000 8,000 6,000 9,600 7,000 11,200 8,500 13,600 10,000 16,000 12,500 20,000 15,000 24,000 17,500 28,000 20,000 32,000 25,000 40,000 30,000 48,000 35,000 56,000 432 528 624 720 840 960 1,080 1,200 1,440 1,680 2,040 2,400 3,000 3,600 4,200 4,800 6,000 7,200 8,400 1,389 1,702 2,020 2,335 2,732 3,135 3,540 3,945 4,770 5,608 6,885 8,197 10,417 12,500 14,584 16,667 20,834 25,000 29,167 129 7.9 2,190 158 8.9 2,680 186 9.7 3,160 215 10.5 3,650 250 11.4 4,250 286 12.2 4,860 322 13.4 5,470 358 14.5 6,080 429 16.4 7,290 500 18.1 8,500 608 20.5 10,330 715 22.5 12,150 893 25.6 15,180 1,072 28.4 18,220 1,250 30.9 21,250 1,429 33.2 24,290 1,786 37.4 30,360 2,143 41.2 36,430 2,500 44.7 42,500 5,500 4,280 5,050 5,840 6,800 7,770 8,750 9,720 11,660 13,600 16;520 19,440 24,280. 29,150 34,000 38,860 48,570 58,280 68,000 525' 643 758 876 1,020 1,166 1,312 1,459 1,749 2,040 2,479 2,916 3,643 4,372 5,100 5,829 7,286 8,743 10,200 1,695 15.7 . 2,089 19.2 2,461 22.6 2,853 26.1 3,335 - 30.4 . 3,830 34.8 . 4,330 . 39.1 4,834. 43.5 5,850 52.1 6,885 60.8 8,490 73.8 10,125 86.8 12,650 108.5 . 15,183 130.2 17,708 151.8 20,242 173.5 25,300 216.9 30,359 260.3 35,417 303.6 Adopted by the Sled Heating RoiUr Institute in cooperation with the Bureau of Standards, United States Department of Commerce Simplified Practice Recommendations R 157-56. 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. The following efficiencies apply to current designs of boilers operated under-favorable conditions at their gross output ratings. Some older boilers designed primarily for hand firing may have lower efficiencies when automatically fired. Anthracite, hand fired--......................................................- 60 to 75 per cent Bituminous Coal, hand fired......... ...................... ............ 50 to 65 per cent Stoker fired.... ............-.................................................. ........ 60 to 75 per cent Oil and Gas fired............ .................... ...... ......................... 70 to 80 per cent Higher efficiencies for hand fired bituminous coal may be obtained by careful firing of either a regular or a smokeless boiler. RATING OF BOILERS In referring to boiler rating it is necessary to know the basis on which the rating has been established in order to understand the exact meaning of the term. The following example will illustrate the meaning of three ratings which might be established for the same boiler. \ ? l r m Heating Boilers 231 Assume that an installation has the following loads determined in accordance with the section Selection of Boilers: Net Load.--..................... ............ ,...................... 1000 sq ft of steam radiation Piping Tax....... ................-................................. 200 sq ft of steam radiation Design Load........ ............................................... 1200sq ft of steam radiation' Pickup Allowance............................. 240 sq ft of steam radiation Maximum or Gross Load..................................... 1440sq ft of steam radiation A boiler that is just large enough to carry this system might be said to have a net load rating of 1000 sq ft, a design load rating of 1200. sq ft, or a gross load rating of 1440 sq ft, depending on the basis on which the boiler is rated. On a net load basis the above boiler would be rated 1000 sq ft of steam radiation and would have sufficient excess capacity to supply the normal piping and pickup load. I=B = R ratings, S.H.B.I'. Net Ratings, and Net Load Ratings of the Heating, Piping and Air Conditioning Con tractors National Association are established on this basis. On a design load basis the boiler would be rated 1200 sq ft of steam radiation and would have sufficient excess capacity to supply the pickup load. It would be of adequate size for a system in which the sum of the net load- and the piping heat loss did not exceed 1200 sq ft of steam radiation. The S.H.B.I. Ratings shown in the first and seventh columns of Table 1 (not to be confused with S.H.B.I. Net Rating) are estab lished on a design load basis. On a gross output basis of rating the boiler would be rated 1440 sq ft of steam radiation and would be. of adequate size for a system in which the sum of the net load, piping load, and pick-up load did not exceed 1440 sq ft of steam radiation. Gross I=B=R Output and A.G.A. Ratings are established on a gross output basis. In the determination of boiler ratings, the Gross Output is the quantity of heat available at the boiler nozzle with the boiler normally insulated and when operating under limitations stipulated in the code or method by ' which the boiler is rated. The boiler may be capable of producing a greater nozzle output but in doing so would exceed some of these limitations. SELECTION OF BOILERS Factors Involved in Boiler Selection The Maximum Load or Gross Load on the boiler is the sum-of the four following items. .. ' The Design Load is the sum of items 1, 2 and 3. The Net Load is the sum of items 1 and 2. 1. Radiation Load. The estimated heat emission in Btu per hour of the connected radiation (direct, indirect, or forced convection coils) to be installed. , connected radiation is determined by calculating the heat losses for each room in accordance with data given in Chapters 4, 5, and 6. The sum of the calculated heat osses for all the rooms represents the total required heat emission of the connected radia- on expressed in Btu per hour. As practically all boilers are now rated on a Btu basis, radiat`nneCeSSary * co"vert ^le radiation load to equivalent square feet of equivalent . ? Hot Water Supply,Load. The estimated maximum heat in Btu per hour required to heat water for domestic use. be y^en water supply is heated by the building heating boiler, this load must taken into consideration in sizing the boiler. A common practice is to add 240 Btu per hour to the radiation load for each gallon of storage tank capacity. For more specific niormation see Chapter 46.