Document aB4pDb4v2reOQMMJb1vXaeDRM

American Society of Heating and Ventilating Engineers Guide, 1932 where Dt -- theoretical draft intensity created by pressure transformer, inches of water. hi = draft loss due to friction in pressure transformer, inches of water. hF = draft loss through the fuel- bed, inches of water. hB = draft loss through the boiler and setting, inches of water. hBr = draft loss through the breeching, inches of water. hv = draft loss due to velocity, inches of water. /iBd = draft loss due to bends, inches of water. he = draft loss due to contraction of opening, inches of water. ho = draft loss due to enlargement of opening, inches of water. hF. = draft loss through the economizer, inches of water. h r = draft loss through recuperators and regenerators, inches of water. The left hand member of Equation 13 represents the total amount of available draft created by the pressure transformer, that is, the natural draft chimney, Venturi chimney, or fan, and is equal to the theoretical intensity less the internal losses incidental to operation. The right hand member represents the sum of all of the various losses of draft throughout the entire boiler plant installation outside of the pressure transformer itself. The left hand member expresses the available intensity and is Table 1. Recommended Minimum Chimney Sizes for Heating Boilers and Furnaces! Warm Air Furnace Capacitt in So. In. op Leader Pipe Steam Boiler Capacitt Sq. Ft. op Radi ation 790 1000 590 690 900 900 1,100 1,700 1,940 2,130 2,480 3,150 4,300 4,600 5,000 5,570 5,580 6,980 7,270 8,700 9,380 10,150 10,470 Hot Water Heater Capacitt Sq. Ft. op Radi ation 973 1,140 1,490 1,490 1,820 2,800 3,200 3,520 4,090 5,200 7,100 7,590 8,250 9,190 9,200 11,500 12,000 14,400 15,500 16,750 17,250 Nominal Dimen sions op Fire Clat Lining in Inches Rectangular Flue Actual Inside Dimensions of Fire Clay Lining in Inches Actual Area Sq. In. 8%xl3 7 xll% 81 13'x 13 nKxii % 127 8%xl8 62^ x \6\6 110 13x18 H%xl6% 183 18x18 15% x 15% 248 20x20 17% x 17% 298 20x24 24x24 17x21 21x21 24 x 24* 357 441 576 24x28* 28x28* 30 x 30* 28x32* 672 784 900 896 Round Flub Inside Diam eter of Lining in Inches Actual Ares Sq. In. 10 79 12 113 15 177 18 254 20 314 22 \ 380 24 452 27 573 Height in Ft. Above Grate 35 40 45 50 55 60 . 65 Dimensions are for unlined rectangular flues fThis table is taken from the A.S.H.V.E. Code of Minimum Requirements for the Heating and Ventilation of Buildings (Edition of 1929). 242 r i fi< d UM ,'-j. c I i Chapter 15--Draft and Chimneys analogous to the head developed by a centrifugal pump in a water works system while the right hand member expresses the required, draft in tensity and is analogous to the total dynamic head in a water works system. For a general circulation of gases, then where Da = Dt (14) D* -- available draft intensity, inches of water. Dt = required draft, inches of water . The draft loss through thefuel bed (Af) or the amount of draft required to effect a given or required rate of combustion, varies between wide limits and represents the greater portion of the required draft. In coal-fired Fig. 8. Draft Required at Different Rates of Combustion for Various Kinds of Coal installations, the draft loss through the fuel bed is dependent upon the following factors: 1. Character and condition of the fuel, clean or dirty. 2. Percentage of ash in the fuel. 3. Volume of interstices in the fuel bed, coarseness of fuel. 4. Thickness of the fuel bed, rate of combustion. 5. Type of grate or stoker used. 6. Efficiency of combustion. There is a certain intensity of draft with which the best results will be obtained for every kind of coal and rate of combustion. Fig. 8 gives the intensity of draft, or the vacuum in the combustion chamber required to burn various kinds of coal at various rates"of combustion. Expressed in other words, these curves represent the amount of draft required to force the necessary amount of air through the fuel bed in order to effect various 243