Document YDYXQ5jQxjxVrv3bdQNLdk0zy

390 CHAPTER 16 . . : , :. i . 195<M>ui<Ie the fuel'rate, the flue-gas rate in pounds per hour may be determined for any fuel. :r It should be noted'that at the higher flows, simulating operation with stoker equipment, the error duetto friction losses will increase as the flow increases, but a reliable determination of the available draft may still be had with only a slight increase in error. DETERMINING CHIMNEY SIZES FOR DOMESTIC CHIMNEYS The flue size for the small domestic chimney is governed by the Building ;Code of the. National Board of Fire Underwriters. It should be noted that these sizes are subject.to revision; hence, the latest edition of the Building Code must be referred to for current minimum chimney-iflue areas. -By calculating the available draft for the chimney in question, and com paring it with the .performance values of the heating unit, either natural FLUE' GAS FLOW-POUNOS PER HR draft or stoker, equipment, at full rating, it is possible to determine whether the chithney is adequate for the particular heating unit it serves. Any. of the .described methods of determining available draft may be used, but a graphical solution to the problem may be had for the. 8. x 8-in. chimney':from,*Figs. 4 and 6. .This solution.can be best explained by a numerical, example. ... Example S. Determine if a 13-ft, 8 x 8-in. nominal-size.flue is sufficient for a coal- heating unit rated at 0.03 in. of water draft at 400 F.inlet temperature, fuel rate being 10 lb per hr of bituminous coal, with 10 per cent COj. .. Solution. From Fig. 6, a flue-gas rate of approximately 180 lb per hr is obtained. The available draft for'a-180 lb per-hr fuel rate, and an inlet temperature of 400 F, obtained from Fig. 4, is 0.056 in.* of water: .This indicates that the chimney is ade quate. . t- .' RELATIVE PERFORMANCE OF VARIOUS TYPES OF DOMESTIC .. . ... CHIMNEYS The clay-lined brick chimney is the most commonly-used chimney,' but recently other building materials have been'used with varying degrees of Success.-'^Tablb 3-shows'a comparison of .the observed draft for two com- Chimneys: and Draft Calculations 391 mon brick chimneys, and a group of chimneys constructed of.various build ing materials.8 ' ` ' ' ; .. .. The following list describes these chimneys: -....... , Chimney 1. Common brick having 6 core holes, H-in.-diam, 7 x 11-in. fire clay flue liner surrounded by air space, 8-in.-diam metal thimble. ` Chimney l. Common brick, 7 x 11-in." fire clay flue liner grouted in with mortar, 8-in.-diam metal thimble. Chimney S. Shale multi-cored tile 3j x 4 x 12-in. in size, 7 x 11-in. fire clay liner surrounded by an air space, 8-in."-diam thimble of tile. Chimney 6. Fire clay multi-cored tile 4 x 5 x 12 in. in size, 7 x 11-in. fire clay tile liner surrounded by an 'air space, 8-inv-diam thimble of tile. Chimney 7. Shale' partition tile having webs and shells approximately ^V-in. thick, 7 x 11-in. fire clay tile liner with an air space, 8-in.-diam thimble of tile. Chimney 10. Cinder concrete building block having two cells, 7 x 7-in. fire clay flue liner-with an air space, 7-in.-diam steel thimble. ..........- - Chimney 11. Same as Chimney 10 except that solid cinder blocks were-use'd.- Table 3. Comparison op Observed-Draft at Standard Conditions for a Group of Chimneys Constructed of Various Building Materials and .Two Common :v'' ' Brick Chimneys 1 .-.s. . ... V Lines, 7 z 7 in. , . ' ... - - 7: '. Eineb, 7- Z 11 IN: ' .. t ,, .. Dbayt In. Water e ' . .. J- : Drajt.In. Water , . * Inlet -Flue-' ; ; . -- : - ... G- Casp-T.e.mp- : . - Common BaicK ClNDEB-CONcbetbBlock Chimney t Chimneys ((10, li; 13,14) V!..: ; .' .- - Gas Temp . . .^ . . :'l v. i. 6; , -' : - Rate of Gas Flow, 20 cfm.' Common Brick . Chimney ' ' ' Brick, ShalE-^, .... TILE, AND., .Chimneys' 'J (1.2. 5, 6, 7,'12)1 V : ..J C^.250-; r 400 > f 6O0P--r : 1000. "' z> 600 1000 V ?;* -------------- 0.053 .072 .086 .115 0.053 .079 .102 .127 0.044^.053.067-.075 .093-1096 - .119-.123 1 . 275. --. 600 `-f 1000 Rate of Gas Flow/70 cfm 0.041-.051 :073^:087 .103-.112 .133-.140 - __ -200.., ` 600 1000 _. 0.055 .088 .-:108 6.052 .102 .131 !. 0.053-.057 .087-.095 -112-.121 : 0.043-1055 v? .108-.113 .138-.144 ..iChimney 12. Cinder concrete chimney unit blocks 17 x 22 x 8 in., designed .to be used with 7 x 11-in. fire clay liner. Except for a spacing boss at themidlength of dach-side, the liner was'spaced I ini from the interior of the unit. Chimney IS. Cinder concrete chimney unit blocks 16 x 16 x 8 in., 7 x 7-in. fire cljay;liner.grouted in Bolid with mortar, 7-in.-diam.thimble.of tile. ,. Chimney 14- Same as Chimney 13,'except that the liner was groute'd only at'the joints. ' , .- : . . . i: .. These chimneys, were all approximately 15.5ft high, and the drafts have been corrected to 29.92 in.'Hg at 32 F. " ' '- ..There are several lightweight chimneys that have been recently approved by the Nalional Board of Fire Underviriters for use with all types of fuel. These chimneys are. constructed of precast masonry or vitreous enameled steel insulated with an insulating material. . The characteristics of these chimneys can be assumed to be approximately those, presented in Table 31 DRAFT REQUIREMENTS OF DOMESTIC APPLIANCES . Typical flue-gas temperatures and drafts, required at rated-,output for several kinds of domestic heating appliances' are contained in . Table 4i