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Theoretical and/or practical limits for the following criteria must be considered for the duct assembly and its elements.

In establishing limitations for these factors, consideration must be given to effects of the pressure differential across the duct wall, airflow friction losses, air velocities, infiltration or exfiltration, as well as the inherent strength characteristics of the duct components.

SMACNA expresses appreciation to the many who have offered suggestions for constructive improvement in the fabrication and installation of duct systems. Special thanks is given to those who volunteered their time, gave their special knowledge and struggled with development of a consensus that would reflect the needs of a diversified industry. In considering such requests, the Association will not review or judge products or components as being in compliance with the document or publication.

Although standardization intrinsically involves selection, no intention of discrimination against the use of any product or method that would serve a designer’s need equally or better exists. Oral and written interpretations otherwise obtained from anyone affiliated with the Association are unofficial.

Atlantic City, NJ Guillermo (“Bill”) Navas, Staff SMACNAChantilly, VA SPIRAL DUCT TASK FORCE Ronald Rodgers, Chairman Phoenix, AZ Phillip Gillespie Indianapolis, IN Richard Graves Houston, TX Spence O’Brien Whitter, CA Robert Seiden Pittsburgh, PA Duct Systems Design ASHRAE Handbook—Fundamentals and Systems and Equipment Volumes ASHRAE—Principles of HVAC ASHRAE Standard 62—Ventilation for Acceptable Indoor Air Quality ASHRAE/IES Standard 90.1—Energy Efficient Design of New Buildings (Except Low Rise Residential Buildings) Model Energy Code of the Council of American Building Officials (CABO) Local Mechanical Codes Corrosion ASM International—Handbook of Corrosion Data (Metals) Corrosion Resistant Materials Handbook (Metal and Non-Metals), NOYES DATA CORPORATION NACE Catalog of Publications Insulation ASHRAE—Handbooks ASHRAE—A Practical Guide to Noise and Vibration Control in HVAC Systems MICA—National Commercial and Industrial Insulation Standards, Endorsed by NIAC Structural Handbooks AISI Cold-Formed Steel Design Manual AISI Steel Products Manuals AISI Design of Light Gage Cold-Formed Stainless Steel Structural Members Cold-Formed Steel Structures—Design, Analysis and Construction, Mc Graw-Hill Publisher, Wei-Wen Yu, Author AISC Manual of Steel Construction MFMA Guidelines for the Use of Metal Framing (Strut Channel) AA Specifications for Aluminum Structures AA Engineering Data for Aluminum Structures ASCE Standard 7, Minimum Design Loads for Buildings and Other Structures FOOTNOTE: Associations whose acronyms are used in texts are: AA—Aluminum Association ACGIH—American Conference of Governmental Industrial Hygienists ACCA—Air Conditioning Contractors of America ADC—Air Diffusion Council AISC—American Institute of Steel Construction AISI—American Iron and Steel Institute ASCE—American Society of Civil Engineers ASHRAE—American Society of Heating, Refrigeration and Air Conditioning Engineers ASTM—American Society for Testing and Materials FHA—Federal Housing Administration MFMA—Metal Framing Manufacturers Association MICA—Midwest Insulation Contractors Association NACE—National Association of Corrosion Engineers NFPA—National Fire Protection Association NAIMA—North American Insulation Manufacturers Association NIAC—National Insulation and Abatement Contractors UL—Underwriters Laboratories Flexible Duct UL Standard 181, for Factory-Made Duct Materials and Air Duct Connectors UL Fire Resistance Directory UL Gas and Oil Equipment Directory NFPA Standard 90A ADC Flexible Duct Performance & Installation Standards ADC Standard FD-72R1 (Thermal, Friction Loss, Acoustical and Leakage Performance) ASTM E 477 (Acoustical Performance) ASTM E 96, Water Vapor Transmission of Materials in Sheet Form Duct Liner NFPA Standard 90A—Installation of Air Conditioning and Ventilating Systems NFPA Standard 90B—Installation of Residence Type Warm Air Heating and Air Conditioning Systems ASTM Standard C 1071, Standard Specifications for Thermal and Acoustical Insulation (Mineral Fiber, Duct Lining Material) ASTM C 167—Thickness and Density of Blanket- or Batt-Type Thermal Insulating Materials ASTM 553—Mineral Fiber Blanket and Felt Insulation (Moisture Absorption) ASTM E 84—Test for Surface Burning Characteristics of Building Materials ASTM C 423—Sound Absorption of Acoustical Materials in Reverberation Rooms ASTM C 916—Specification for Adhesives for Duct Thermal Insulation (Flammability, smoke development, bond strength, flash point, moisture and temperature effects, edge burning characteristics) ASHRAE Handbook—Applications Volume (Sound and Vibration Control) ACGIH—Threshold Limit Values Mil Spec A-3316B—Insulation Adhesives NAIMA—Fibrous Glass Duct Liner Standard Underground Duct Ducts in Concrete Slabs or Under Slabs This document or publication is prepared for voluntary acceptance and use within the limitations of application defined herein, and otherwise as those adopting it or applying it deem appropriate. Its application for a specific project is contingent on a designer or other authority defining a specific use.

They are subject to revision as further experience and investigation may show is necessary or desirable.

With the many available systems sizing methods (e.g., equal friction, static regain, velocity reduction, total pressure) and system types, performance cannot be economically optimized unless the designer selects construction details appropriate for the given pressure and velocity.

Generally speaking, duct strength, deflection, and leakage are more functions of pressure than of velocity.

Systems should be designed using accepted engineering practice and data such as that in the four ASHRAE Handbooks and the SMACNA HVAC Duct Systems Design manual.A duct system may contain ducts under positive and negative pressure. At coils and filters, the velocity may vary from below 1000 fpm (5.08 m/s) to over 3000 fpm (15.24 m/s).Velocity in duct mains and branches can be at constant (high or low) or varying levels.A quick overview of the changes is provided in the front of this manual. SMACNA, does not, however, endorse individual manufacturers or products.Meanwhile, a Committee has already begun work on what will be either addenda or a new edition. A formal interpretation of the literal text herein or the intent of the technical committee associated with the document or publication is obtainable only on the basis of written petition, addressed to the committee and sent to the Association’s national office in Chantilly, Virginia, and subsequent receipt of a written response signifying the approval of the chairman of the committee.

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