Document evyerq2E67mR86LMQROzggVwG

II 333322 W. N. WITHEHIDGE !, through any branch is too high, further closing of a damper increases the loss through that branch; this makes it possible for a smaller volume of air flow|tplc) necessary pressure drop for a condition of balance. "Slllll 15. If necessary, after the system is balanced on paper to a reasonable degieemi ing the round duct sizes, conversion to rectangular duct sizes can be made by usm|jp| Summarize the System Resistance ---- 16. Determine the adjusted total pressure drop of the branch and main in'r 1 adding the pressure losses beginning with any one exhaust opening and proceeding, fan or dust collector. Remember that so long as the branch duct system ha.' U >i, balanced in accordance with item 14 above, it will be a simple matter to i_l<` l starting point for totaling the pressure losses. However, if no balancing is atti mptlm! losses must be estimated for the single run of duct that you believe will have t'he^rfqj SM4RP ENTRANCE Enironc* loti 0.9 VP Hood Suction 1.9 VP CONVERGING ENTRANCE FUNGED ENTRANCE Enironc* loss 05 VP Hood suction 1.5 VP a Ad Entroncs loss 0.13 VP 15* 025VP JO* 0.45 VP 15* 050VP . Figure -19,~Exhaust- hood- entrance losses in relation to velocity pressure (VP). (Courtesy American Air Filter Co., Louisville.) 90 73 100 125 150 175 200 23 CEN7ERUNE RADIUS IN PER CEN7 OP PIPEloiAwEmf! ...'Tigufe "207-'Pipe-elbow fnctjffis|H terms of pipe diameters. (Reprinte^^M sion from Heating, Ventilating, ing Guide, 1960, Chapter 31.) resistance Experienced designers after a few moments of inspection usually canj'deiujirim^ "longest run" in terms of friction loss. In this case the "longest run" impliessth'^gw^ffl offers the greatest resistance to air flow, and not necessarily the one longest in ier'-nsicLtuctfi 17. Add the resistances of accessory equipment such as air cleaners, weath; imjffi shutters. Since this type of equipment varies greatly in resistance to air flqii:]sma&|fffi^ffi data should be consulted. --i'JisjiSi Select an Appropriate and Adequate Fan or Air Mover , __J.iJEffini-IheuAPtal.ait.flow-iru.c.f.mrand~tha'total-sy8tem-re8istan'tre'"OrpS5ljjij^^| water, select froni^manufacturers' catalogs a fan of the type, size, and;speed|tbTgi"^|oS^^ operating efficiency or lowest H.P. consistent with other considerations, as !qutiinf|cl*Np.at 326-338. Note that the total resistance of the system does not include at the entrance to the exhaust hoods. J B. DESIGN EXAMPLE J Figure 24 is a line diagram of a simple grinding exhaust sy'Vs1*'"temi itDu* 'vjijrLa been aerodynamically designed according to the plan outlined above TlujCgyjj are summarized in Table 16. v'Tr1