SECTION 15841 LOW PRESSURE DUCTWORK PART 1 GENERAL 1.01 SUMMARY A. Related Sections: 1. 07270 - Firestopping and Fire and Smoke Barrier Caulking. 2. 15260 - Vibration Isolation. 3. 15280 - Thermal Insulation (HVAC). 4. 15855 - Air Handling Units. 5. 15910 - Duct Accessories. 6. 15940 - Outlets (HVAC). 7. 15990 - Tests (HVAC). 1.02 REFERENCES A. Sheet Metal and Air Conditioning Contractors' National Association (SMACNA), latest edition: 1. HVAC Duct Construction Standards (Metal and Flexible). 2. High Velocity Duct Construction Standards. B. National Fire Protection Association (NFPA): C. National Electrical Code - 1999 (NEC) - 70. D. American Society of Heating, Refrigerating, and Air-conditioning Engineers, Inc. (ASHRAE) 62 - Ventilation for Acceptable Indoor Air Quality. 1.03 SUBMITTALS A. Ductwork: 1. 1. Provide 1/4" scale composite Shop Drawings. Shop Drawings shall be coordinated with other trades before submitting. 2. 2. Catalog Cuts: Low pressure ductwork, duct sealer, and turning vanes. 3. 3. Catalog Cuts, Ratings, and Performance Data: Flexible ductwork. B. Casings, Plenums, and Housings: Details of construction. C. Provide details of proposed typical ductwork fittings including: 1. Seams and joints. 2. Joint sealing. 3. Elbows, vaned and radius. Project No. SPECIFICATION GUIDELINES 15841-1
4. Transitions and Offsets. 5. Taps and outlet frames. 6. Branch connections and tees. D. Duct Hanger System: Catalog cuts and shop drawing. PART 2 PRODUCTS 2.01 MANUFACTURERS A. Flexible: Genflex or Flexible Technologies. B. Ductwork and Fittings: 1. Metalaire. 2. Semco. 3. Spiramatic. 4. United Sheet Metal. C. Ductwork Adhesive Sealing Compound: 1. Interior: a. Benjamin Foster #30-02. b. 3M Hardcast. 2. Exterior: 2.02 MATERIALS a. Flexomastic No.210 with fiberglass membrane for weatherproofing as manufactured by Weatherproofing Products, Inc. or accepted equivalent. A. Ductwork shall be fabricated and installed according to the SMACNA Standards, except as shown on drawings or specified. B. Ductwork shall have manufacturer's gage stamp intact. 2.03 LOW PRESSURE DUCTWORK A. Includes ductwork from low pressure air handlers, exhaust, and outside and return air ductwork. Velocities shall not exceed 1600 fpm for rectangular and 2,000 fpm for round ductwork. Static pressures not to exceed 2 inches WG. B. Provide galvanized steel ductwork, designed, constructed, installed and tested according SMACNA - "HVAC Duct Construction Standards" and as shown on drawings. Ductwork to have manufacturer's gage stamp. Provide cross-breaking or beading to prevent flexing, but do not reduce gage of metal below that required for flat ductwork sheets. Minimum gauge for all ductwork shall be 24 gauge. 1. Ductwork gages shall comply with the following: Project No. SPECIFICATION GUIDELINES 15841-2
Greatest Dimension US Gage 0" to 12" 24 13" to 30" 24 31" to 60" 22 61" to 90" 20 over 90" 18 2. Ductwork dimensions shown on the drawings are clear inside dimensions. C. Splitters and Dampers: 1. Provide as shown and as necessary for proper regulation of air distribution system. 2. Locate dampers to be easily adjustable after work is completed. Provide a set screw locking device for each splitter or damper. On insulated ducts, place locking device on a bracket so set screw is on surface of insulation and is easily operable. Provide Armaflex plug. Use Ventlock or Young Regulator. 3. Sheet Metal Gage: Construct splitters and dampers of galvanized steel 1 gauge heavier than duct where installed. D. The following ductwork and plenums shall be insulated, unless noted otherwise. 1. Outside air ductwork at air handler=s closet. E. Flexible Insulated Ductwork: 1. Lightweight duct, core of corrosion resistant reinforcing wire helix permanently bonded within fabric, insulated with 1-1/2" thick, 3/4 lb. density fiberglass flexible insulation and covered with a vapor barrier of aluminum metalized polyester film laminated to glass mesh, elastomer back coated. Duct shall meet NFPA 90A requirements and be listed as Class 1 Air Duct Material, UL 181. Minimum R=6 insulating value. 2. Flexible Collar Connections: Make connections to and from units with collars not less than 4 inches long, secured by peripheral strap iron, using 30 ounce neoprene coated glass fabric by Ventglas or accepted equivalent. Collar connections from rectangular ductwork to flexible ductwork shall be "Low Loss". 3. Manufacturers: a. Atco Rubber Products. b. Genflex. c. Thermaflex II. d. Venture Type VTKC. e. Wiremold Co. F. Turning vanes shall be provided in square elbows and shall be of same material as the ductwork. Turning vanes shall be of airfoil type, double thickness factory fabricated. Project No. SPECIFICATION GUIDELINES 15841-3
G. Install ductwork materials and accessories according to the latest edition of SMACNA Low Velocity Duct Construction Standards as specified. These written specifications shall take precedence in case of conflict. H. Thoroughly clean ductwork before attempting test and balance. I. Where interferences arise during construction, make transition or division of ductwork on a basis of pressure drop equivalent to the original size. Obtain acceptance from A/E before fabrication. J. Seams And Joints at Exhaust, Supply, Return and Outside Air Distribution Systems: All joints shall be sealed whether longitudinal or transverse Make airtight as possible. Seal joints with 4 inch wide cloth tape with adhesive sealing compound, except ductwork exposed to weather shall have joints sealed with specified joint sealant. K. Apply Flexomastic weatherproofing with smooth finish to joints of ductwork exposed to weather as recommended by joint sealant manufacturer, with at least 2 final coats of No.210. L. Sound Levels: Discharge sound levels for occupied areas shall not exceed a rating of RC 35 as defined in ASHRAE. PART 3 EXECUTION 3.01 GENERAL A. Install ductwork as shown on drawings. B. Before systems are tested and balanced, ducts shall be thoroughly cleaned and blown out. C. Where interferences arise during construction, make transition or division of ductwork on basis of pressure drop equivalent to original size. Obtain approval from A/E before fabrication. 3.02 INSTALLATION A. Install ductwork materials and accessories according to the latest edition of SMACNA Low Velocity Duct Construction Standards as specified. In case of conflict with these specifications, the most restrictive shall govern. B. Seams and joints in all ductwork shall be made airtight. Seal duct joints with sealer as specified for field sealing of high pressure ductwork. Make exhaust ducts passing through return air chases airtight. C. Install flexible ductwork shall be installed in sizes to match diffuser necks as indicated on drawings schedules. Duct length shall be not less than 5 feet and no longer than 8 feet. Duct shall be adequately Project No. SPECIFICATION GUIDELINES 15841-4
supported to prevent kinks and sharp bends. Install according to manufacturer's recommendations and as shown on drawings. 3.03 DUCTWORK SUPPORTS AND HANGERS A. Provide support and hangers according to SMACNA HVAC Duct Construction Standards. 1. Hangers: Hang horizontal ducts at intervals not exceeding 8 feet, with hangers of 16 gage by 1 inch wide galvanized band iron on ducts up to and ncluding 30 inches wide and 12 gage by 1-1/2" wide galvanized band iron on ducts over 30 inches wide. Extend hangers down and fasten underneath duct in addition to both sides of duct. B. Hanger straps shall be hung from inserts or clip angles secured to structure with expansion bolts in shear or tension as follows: 1. Roof Slab: In tension. 2. Structural Beams: In shear, 12 inches minimum from bottom of beam. 3. Joists: Use existing forming bolts openings only. Hangers shall be bent under ductwork at least 2 inches. Hangers for ducts over 48 inches wide shall be secured to bottom and sides of duct. 3.04 DUCT PENETRATIONS TO FLOOR AND FIRE WALLS A. Joints around duct penetrations shall be packed with fire safing insulation and sealed with fire and smoke barrier caulk as specified in Section 07270, Firestopping and Fire and Smoke Barrier Caulking. END OF SECTION Project No. SPECIFICATION GUIDELINES 15841-5