plenum boxes

Publication DIFFUSERS section 2 SEPT 2005 Part H R Air Diffusers supply and exhaust ventilation systems plenum boxes The general range of PB plenum boxes are manufactured with a return edge hem in the neck to suit the yoke strap fixings supplied with LCS, Flowline and F45L diffusers. The boxes can be manufactured to suit either top or side entry duct arrangements and are available with square rectangular or circular spigots. Optional spigot mounted flap dampers are available with either cord or quadrant operators. Plenums can also be supplied with a non fibrous fire resistant acoustic liner for applications with critical noise limits. The plenum selection nomogram on page 20 is designed to optimise the cross sectional area of the box to ensure an even distribution of air along the length of the diffuser. To select an appropriate plenum size, firstly establish the static pressure loss of the diffuser at the required design duty from the appropriate performance table. Then, using the selection nomogram, project a line between the flow rate and pressure loss scales to the pivot line of the plenum dimension scale. From there, project a line from the appropriate diffuser slot width through the pivot point and read off the plenum height. Note, an allowance should be added to the height to allow for the depth of the diffuser frame refer to note on the plenum height scale. If the ceiling void height is limited, then any combination of width and height can be selected about the pivot point providing the plenum height can accommodate a suitable spigot size. To determine the spigot size, project a line from the flow rate scale through the required spigot air velocity to the diameter line. Square or rectangular spigots of equivalent area can also be selected using the spigot diameter as a pivot point. Linear diffusers PLENUM BOXES introduction options plenum selection type PB 2 dimensions ordering details type option height PBH / FDQ / AL12 / 1200 / 3F / 435 / 315SE / 4 length quantity EXAMPLE : control width spigot *P - Neck dimension to suit diffuser type. See appropriate diffuser dimension table. *H - O/A Height including allowance for depth of diffuser. *N - Flowline diffuser = 85mm LCS = 82mm F45L = 45mm PBL PBH W Top Entry (TE) *H *N *P i/s D 25 50 Side Entry (SE) W D 25 *H *N L i/s Dia D A B End Cap detail for single diffuser sections. Damper options FDC - Cord operated Flap FDQ - Quadrant operated Flap Optional Acoustic Liner AL12 - T = 12mm AL25 - T = 25mm Allow for liner thickness when sizing plenum. T D + 50 D Linear diffusers PLENUM BOXES R 3 Linear diffusers WIDTH (mm) HEIGHT PIVOT (mm) LINE GRILLE PRESSURE LOSS (Pa) SPIGOT AIR VELOCITY (m/s) APPROXIMATE NR LEVEL (OPEN DAMPER) 50 40 30 20 75 100 150 50 200 300 400 500 50 100 300 200 75 600 100 150 200 250 400 500 600 800 1000 300 125 150 200 250 300 500 600 500 600 5 4 3 2 125 400 100 1 50 20 10 5 125 200 250 315 600 400 160 PLENUM DIMENSIONS WIDTH (mm) HEIGHT (mm) PIVOT LINE RECTANGULAR OR SQUARE SPIGOT AIR FLOW RATE l/s m3/hr 1000 900 800 600 500 400 300 250 200 700 100 3000 2000 1500 1000 900 800 700 600 500 400 50 300 200 150 400 SPIGOT DIAMETER (mm) SELECTION NOMOGRAM 1F LCS1 2F LCS2 3F LCS3 4F LCS4 5F LCS5 6F LCS6 7F 8F 4 example note Select a suitable plenum size for a 1.2m long 3F diffuser supplying 270 l/s. Air flow rate (l/s/m) = 270/1.2 = 225l/s/m, which from the chart on page 11 gives pressure loss of 18Pa. From the nomogram, an active plenum height of 300mm would be satisfactory with a 400mm x 200mm spigot, but to accommodate an equivalent size circular spigot the plenum height would need to be increased to 350mm. The overall plenum height with a circular spigot would therefore be 350 + 85 = 435mm. NOTE - to allow for the depth of t

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