Duct System Design Guide - McGill AirFlow

1 duct System Design GuideFirst Edition 2003 McGill AirFlow CorporationMcGill AirFlow CorporationOne Mission ParkGroveport, Ohio 43125 duct System DesigniNotice:No part of this work may be reproduced or used in any form or by anymeans graphic, electronic, or mechanical, including photocopying,recording, taping, or information storage and retrieval systems withoutthe written permission of McGill AirFlow performance data included in this Guide have been obtained from testing programs conducted in flow measurement laboratories and detailedin the reference test reports. The data are reprinted in this manual as asource of information for Design engineers.

2 McGill AirFlow Corporationassumes no responsibility for the performance of duct System componentsinstalled in the AirFlow Corporation is a wholly owned subsidiary of United System Design iTable of Contents An Overview of the Design How to Use the duct System Design Chapter 1: AirFlow Fundamentals for Supply duct Conservation of Continuity Diverging Conservation of Static Velocity Total Pressure Loss in duct (Friction Loss).. Round Flat Oval Rectangular Acoustically Lined and Double-wall Nonstandard Pressure Loss in Supply Loss Diverging-flow Fittings: Diverging-flow Fittings: Straight-Throughs, Reducers, and Miscellaneous Nonstandard Chapter 2: Designing Supply duct Determination of Air Volume Location of duct Selection of a Design Equal Friction Constant Velocity Velocity Reduction Static Regain Total Pressure Which Design Method?

3 Equal Friction duct Determination of System Excess Static Regain duct Determination of System Excess duct System Design ii Chapter 3: Analyzing and Enhancing Supply duct Systems Analyzing a Preliminary Supply Balancing Equal Friction Balancing Orifice Enhanced Equal Friction Enhanced Static Regain Fan System Effect Performance duct Performance Fan Cost Chapter 4: AirFlow Fundamentals for Exhaust duct Systems Conservation of Continuity Converging Conservation of Pressure Pressure Loss in duct (Friction Loss).

4 Pressure Loss in Return or Exhaust Fittings (Dynamic Losses).. Nonstandard Conditions for Dynamic Chapter 5: Designing Exhaust duct Defining the Application and Determining Determining Capture Velocities and Air Volume Locating duct Determining duct Sizes Based on Velocity Mixing of Two Air Determining System Pressure Chapter 6: Analyzing Exhaust duct Fitting Balancing the Using Using Corrected Volume Flow Using Smaller duct Sizes and Less Efficient Specifying and Selecting a System Chapter 7: Acoustical Sound Power and Sound duct System Design Chapter 8.

5 duct System Fan Natural duct Wall Elbow Sound Power End AirFlow -Generated Radiated duct Break-Out Break-In Nonmetal Chapter 9: Room Air Terminal ASHRAE Room Design NC Rating RC Rating Criteria Design Other Spectrum Chapter 10: Supplemental Attenuation Calculating Attenuation Double-Wall Insulated and Single-Wall Lined duct Noise Attenuation of Insulated duct Dissipative Reactive Active No-Bullet Computer Appendix: General Glossary of Conversion Area/Diameter Tables and Round duct Size and Spiral Flat Oval duct Shape Conversion Nonstandard Condition Correction Velocity and Velocity duct System Design iv Product Metal Gauge.

6 Thickness and ASTM ASTM ASTM ASTM ASTM ASTM ASTM ASTM ASTM McGill AirFlow Corporation Manufacturing Industrial Manufacturing Derivation of the Continuity Derivation of TP= SP+ Derivation of Velocity Pressure Darcy-Weisbach Equation for Calculation Friction Surface Derivation of Pressure Loss in Supply Derivation of Presssure Loss in Exhaust Negative Loss Derivation of the Inlet Static Pressure Loss Pressure Loss Data .. Single-Wall duct Friction Loss k-27 Correction Round-to-Flat Oval Transition, C vs.

7 Round Slip Coupling, C vs. Acoustical Double-Wall Round Flat Oval Rectangular Single-Wall Round duct Installation of Single-Wall duct and Installation of Double-Wall duct and UNI-COAT duct and Specifying duct Recommended Specifications for Commercial and Industrial Construction Specification Institute (CSI), Alexandria, Production Systems for Architects and Using Computers for duct UNI- duct duct System Design v ASHRAE duct Fitting Database ASHRAE Algorithms for HVAC HVAC Systems duct Design , Sheet Metal and Air Conditioning Contractors National Association (SMACNA), 1990 Chantilly, 95 ASHRAE Handbooks, American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), Atlanta, Air Diffusion Council Publications (ADC), Chicago, American Socitey for Testing and materials (ASTM)

8 , Philadelphia, American Conference of Governmental Industrial Hygienists (ACGIH), Cincinnati, OH Air Movement and Control Association (AMCA), Arlington Heights, T-Method by Robert Tsal (see reference ASHRAE Fundamentals Handbook). Engineering Report 151, Flat Oval- The Alternative to Rectangular (see Part IV EDRM, Supplementary Topics by United McGill Corporation).. Engineering Report 102, Effect of Spacing Tees (see Part IV EDRM, Supplementary Topics by United McGill Corporation).. Noise Control for Buildings and Manufacturing Plants, Bolt, Beranek and Newman, Inc., duct System Design viINTRODUCTION Foreword These reference manuals have been compiled and written by engineers and consultants employed by United McGill Corporation and its subsidiary, McGill AirFlow Corporation.

9 McGill AirFlow Corporation is the nation=s foremost producer of sheet metal duct and fitting components for air handling systems. In over 50 years of serving the mechanical System marketplace, McGill AirFlow has gained a technical expertise, which is unmatched in the industry. This publication shares a part of that expertise with the engineers, designers, contractors, and specifiers who Design and install duct systems, Although there is an abundance of published literature concerning mechanical System Design , there is very little information specifically about duct System Design condensed into a single document.

10 What does exist is difficult to understand. There is a wealth of information available concerning air volume determination (heating and cooling loads), fan selection and specification, terminal and/or box selection, room air distribution, etc., but very little is written about the duct and fittings used in duct systems. This publication is an attempt to remedy that situation. There are many methods for producing acceptable supply duct designs. In this notebook, three methods for positive pressure Design will be addressed: equal friction, static regain and total pressure. This is not meant to exclude other Design methods; however, these are the most popular.