الحمد لله والصلاة والسلام على رسول الله وعلى آله وصحبه أجمعين DUCT WORKS Selection Tips DETAILED TECHNICAL SPECIFICATION A. All ducting must be made of galvanized steel sheet to ASTM A525 lock-forming quality, having zinc coating of 275gm/M² for both sides in accordance with ASTM A90 and of tensile strength 28/33 tons per square inch B. All ducting must be made as indicated in the installation drawings and successful tenderer must check the installation and building before hand and ensure that the existing structures, etc., must not come in the way of ducting at time of installation Dimensions of ducting can be altered by the contractor with the prior approval of concerned Engineer without altering permissible airflow rates C. All ducting must be suitably stiffened to avoid vibration, sagging and running effects due to airflow. All ducting must be made airtight D. Gauges of G.I sheeting, type of joints, bracing, etc., used for the manufacture ducting must be as shown below E. The throat radius of bend must not exceed half the width of associated side of the duct and where it is not possible to comply with this duct turning vane must be used along with the right angle bends The duct turning vanes must be spaced in such a way that the speed ratio of each of the individual elbows must be around 6:1 Maximum Side inches US Standard Gauge Transverse Joints and Bracing 154BUp to 12" 24 ¾” pocket or slip joint at 8 ft. centres 13 – 18” 24 1” pocket joint at 4 Ft. centers with cross breaking 19 – 30” 22 1” pocket joint at 4 Ft. centers with cross breaking 31 - 42” 22 1½” pocket joint at 4 Ft. centers with cross breaking and ½ x ½ x 1/8 angle with girth at 8 ft. centres bolted to the pocket joint 43 – 54” 20 1½” pocket joint at 4 Ft. centers with cross breaking and 1½ x 1½ x 3/16 angle with girth at 8 ft. centres bolted to the pocket joints 55 – 72” 20 1½” pocket joint at 4 Ft. centers with cross breaking and 1½ x 1½ x 3/16 angle with girth at 4 ft. centres bolted to the pocket joints 73 to Up 18 2½” x 1½” x 3/16 angles at 4 Ft. centers bolted to the duct with 3/8 bolts at 1½ centers and fastened together with 3/8” bolts at 2 centres with rubber gasket between the 2 angles and cross breaking Joints 50 mm Slip Joint or Draw Band is acceptable through 1500 mm size Slip or Draw Band Joint Flanged Joint All tees, Bends and Elbows must be constructed with radius of not less than 1½ times diameter of duct on centerline Where not possible and where rectangular elbows are used aerofoil-turning vanes must be provided Transformation of duct sizes must be gradual, not exceeding 15 degrees divergence and 30 degrees convergence Round duct fittings must be of welded type construction For ducts of diameter up to and including 300-mm. diameter one-piece smooth 90 deg. elbows must be used. Over 300-mm dia they must be 5 piece welded Turning Vanes must be fabricated in accordance with SMACNA Standards Turning vanes must be as follows Factory or site-fabricated using factory-fabricated vane spacing rails Turning vanes must be provided in all square elbows, take-off or extension collars to supply outlets and tap-in branch take-off connections Turning vanes must be reinforced by rods or of sectional construction Turning vane arrangements and thickness must be as shown 153 B SINGLE 152 B VANE 151 B SCHEDULE Type Space between Vanes Radius Gauge Small Large 1½” 3” 2” 4½” 24 22 Volume Control Damper Volume control dampers must be provided in ductwork to regulate and balance air systems, since dampers on the air inlet and outlet must be used only for fine secondary regulating or balancing The damper must be fabricated in accordance with SMACNA Duct Construction Standards Single blade dampers must be used for damper widths up to 300 mm provided that there is sufficient length of straight duct after the damper to ensure equal flow before the next take-off or outlet Where the damper width is over 300 mm. multi -blade dampers must be used Multi blade dampers styles must be generally parallel blade for two-position operation and opposed blades for modulating position The blades must be constructed of galvanized sheet, suitably stiffened by forming or other method, and assembled in prime coated or galvanized channel frame with suitable hardware The bearings must be of bronze or oil impregnated nylon Looking and indicating quadrant regulator must be provided for each damper The indicating quadrant must be clearly marked to indicate close, ¼, ½ , ¾ and open positions On insulated ducts, quadrant regulators must be mounted on stand off mounting brackets or bases For motor operated damper, the motor-operator must be electric type Fire Dampers must be fabricated in accordance with NFPA 90A and UL 555 or equivalent and must be 1• To be provided in ducts and openings in shafts, floor firewalls, fire partitions and the rated ceilings 2• In horizontal ducts, fire dampers may be single or of a multi blade type. In vertical ducts only single blade type must be used 3• Galvanized sheet metal housing to be provided with angle flanges on both sides 4• The damper must be of 1.6 mm thick sheet steel or steel/mineral fiber/steel sandwich of equivalent fire resistance, thermally released 5• Fire dampers must be equipped with fuse plug, positioning levers fittings and position indicator accessible from outside Grilles and Registers They must be furnished with sponge rubber gaskets or foam tape behind the frame to eliminate air leakage and with nylon bushings or PVC at the blades connection to the frame to eliminate corrosion and vibration. Free cross-sectional area must be at least 65 percent 1- Supply air registers and grilles must have individually adjustable horizontal front blades and vertical rear blades 2- Supply air register must be equipped with key operated, opposed blade volume control damper 3- Return and exhaust air registers and grilles must have fixed single deflection blades set at an angle of 35 degrees 4- Return and exhaust air registers must be equipped with key operated, opposed blade volume control damper 5- All opposed blade volume control dampers must be polyester powder coated ovens taken with black colour finish Jet Diffusers must have manual discharge pattern adjustment from the front or back of diffuser, the outer flange of the jet diffuser to be made of aluminium, the inner core and rings to be made of mild steel construction, to be coloured by electrostatic polyester powder coating finish Access Doors Airtight access doors with rubber linings must be installed in all ducts at fans, filters, heaters, fire dampers and volume dampers for inspection cleaning and maintenance purposes The opening in the ductwork must be properly stiffened at the edges with frames riveted or welded to the duct The access door must be All Access Doors mounted on insulated ducts must be of sandwich type, having the same insulation thickness as that of the duct, with Cam Lock handles Maximum Size(mm) No. of Hinges No. of Handles Door Gauge Back Frame 12” x 12” 2 1 26 26 24 16” x 20” 2 2 24 26 22 24” x 24” 3 2 22 26 22 Flexible Connections Flexible connections must be fitted on all suction and discharge connections of fans and air conditioning units, for preventing transmission of vibration through the ducts to occupied spaces Flexible connections must be made from flame proof, factory fabricated from chemically impregnated canvas Connections must fit closely and be secured in an airtight fashion to duct work, fans and apparatus by means of angle iron or flat iron frames. The unclamped section of the flexible connection between the apparatus and the ductwork must be not less than 150 mm. in length. Flexible connections must not be painted Supports and Hangers Installation of supports and hangers must be Supports and hangers must be attached only to structural framing members and concrete slabs. They must not be anchored to metal decking unless a means is provided and approved for preventing the anchor from puncturing the metal decking Supports must generally be made from galvanized steel sections and where heavy items of equipment occur within ductwork additional support must be provided as necessary Duct work hung from inserts or from clip angles must be secured with expansion bolts in shear. Supports for horizontal ducts must be RECTANGULAR DUCT Length of Longer Side (mm) Drop Rod Diameter (mm) Bearing Member (mm) 155BMaximum Spacing ( inch) 156 B up to 12” 8 20 x 3 Flat 120” 157B Over 12” up to 24” 8 25 x 25 x 3 angle 120” Over 24” up to 40” 10 40 x 40 x 4 angle 100” Over 45” up to 64” 10 50 x 50 x 5 angle 100” Over 64” 15 75 x 75 x 6 angle 100” Design of supports for vertical ducts will be dictated by site conditions and spacing may be greater than for horizontal ducts Supports for vertical ducts must be angles and channels made of galvanized or painted black steel Vertical duct must be fastened with a minimum of 2 supports at each floor في أمان الله
