Document pee0QjVabGxwpMrLyNkGXndpD

CHAPTER 32 1956 Guide -Air Duct Design - 753 F ia . 12. St a t ic R e g a in C h a b t * D e te rm in in g V e lo city in D ucts C a rry in g 0 to S000 cfm Under the best practice, 0.7 to 0.8 of the change in velocity pressure is actually recovered, but for practical design an average recovery of 0.5 is assumed. Hence, the actual regain Pr is: -(f\ Design charts based on Equation 13 and rectangular ducts having aspect ratios of 3 to 1 or less are presented in Figs. 12 and 13. The duct length of any section should include the equivalent length o any elbows or transitions within the section. The charts apply to construc tions where regain takes place unaccompanied by radical change in direc tion; namely, to straight-through sections of divided-flow fittings. i ian SoliTM , iiegain iviecnodj. A duct layout is shown in Fig. 14. The 6 1000 cfm^80?0 Outlets b 2> 3 and 4 deliver 1500 cfm each, and outlets 5 and tronk veWn ' The aerating pressure loss at all outlets is 0.12 in. water. Initial soft and thiy ?S ass.V,n?ed,oS fPm; the area of the trunk duct will then be 5.33 *llJable tomainfin be f \l ln' J1" assumed "that for this example it is desir- Sectiom^B P r> uV' ueth al1 d"ct sections Determine the sizes of duct aZJh'Jtobtained aatt each of ithife ouxtl,e9ts8,0and finsdubthsetatnottiaalllpyrethsesusraemloessstoaftitcheprseyssstuerme .will be Solution: F byAfrictionZlo^eoC.tin thec,equal friction method so that it has the same rate of and the mif section A. Section A is equivalent to a 29.2 in. round duct (Table 1) rate of nrl e.l0SS f5?m.Plg- 3 13 013 in- Per 100 ft. For 2000 cfm flowing at this p essure loss, the indicated round duct diameter for Section F is approxi-