Document QgBkdXBLDM0pa2EwqaXgpvXEL

T a b l e 1. C ircular E q uivalents op R ectangular D ucts for Eq ual F rictio n-- (Continued) American Society, of Heating and Ventilating Engineers Guide, 1932 - .Chapter 32t-^Air Distribution Systems a - Example s.' If. the longest run of pipe is 70 ft, the mean of its two dimensions 25. in. aiid it has. 4 elbows,'then F = 214 + '70 ' +'4/5 -- 4 velocity, heads loss in the duct. 2000 The velocity which will cause a. loss of K in. will then be V = -- ,= 1000 fpm. Main Trunk Ducts with Branches. A main duct with branches is generally used to convey tempered air for ventilation purposes only. In place of individual ducts a comparatively large main duct supplies air by branches to various rooms with a velocity which may be 2000 fpm at the start and reduced to 400 fpm in the risers, these figures varying according to the nature of the installation. This duct system may be designed so that the loss of pressure in the branches is equalized in a manner similar to that previously described. For each branch a factor, may be calculated by Formula 6. It is usually desirable that the loss in; each branch approximate 0.1 in., or since the velocity corresponding to 0.1;in. is 1260 fpm, the factor F and the velocity V will give a loss of 0.1 jin. if V = 1260 I - . VF. :{ Example 4. Table 2 is a schedule for an air distribution system of a typical school: (see,Figs. 6 to 10 inclusive). The volume of air per minute for classrooms is based on the. nuniber of pupils, with an allowance of 30 cfm per pupil. Table 2 shows the volume of: air to be delivered to each room, and also gives the dimensions of the risers, the size of the diffusers and the velocities through each. :i The total air requirement for the building is 24,050 cfm. To provide a margin for some unavoidable leakage, the total volume should be increased 10 per cent, and. this increased volume should be used as the basis for determining the size of the main ducts, and:branches, although the 10 per cent added may be disregarded in arriving at the, size;of the risers and diffusers, inasmuch as any leakage will probably have occurred' before the air reaches this point. ;i Table 2. Air Schedule for Typical School Layout Room No. Cubic Con tent Dimensions Feet Sq. Ft. No. or Air Req. Floor Pupils peb Min. Size Riser Inches Velocitt (fpm) - Size Diffuser (Inches) Diffuser Velocitt (fpm) i 2,3 4 5. 6 7 :8 9 10 11 12 -13' 14 15 16 17 Audi. Office 7000 26)^x22x12 .7000 26)^x22x12 7000 26)4x22x12 7000 26)4x22x12 7000 26)4x22x12 '7000 26)4x22x12 8720 33 x 22x12 8720 33 x22x 12 7000 26)4x22x12 7000 26)4x22x12 5800 22 x 22 x 12 . 7000 -26)4 x-22-x-12 3360 21)4x13x12 3360 21)4x13x12 17500 54 x 27 x 12 6480 20 x27 x 12 7000 .26)4 x 22x12 37600 65 x 34 x 17 3700 14 x 22x12 583 . 583 583 583 583 583 726 726 583 583 483 583 280 280 1460 540 583 2220 308 40 40. 40 40 40 40 50 50 40 40 33 40 20 20 100 37 40 1200 16x20 .1200 .. 16x20 1200 16x20 1200 16x20 1200 . . 16x20 1200. 16x20 1500 16x24 1500 16x24 1200 16x20 1200 16x20 990 16 x 16 1200 16x20 600 12x16 600 12x16 3000 2-16x24 1110 16x20 1200 16x20 2500 2-16x20 250 8x12 540 540 540 540 540 540 . 563 563 540 540 556 540 450 450 465 503 540 565 375 20x30 288 20x30 288 20x30 288 20x30 288 20x30 288 20x30 288 24x30 300 24x30 300 20x30 288 ,20x30 288 16x30 297 20x30 288 16x20 270 16x20 270 24x30 ' 300 20x26 289 20x30 288 20x30 301 12x12 250 463