A Field Perspective on Engineering Commissioning Resources
  • Home
    • What's New
  • Blog
    • Blog Support
  • SketchUp Models
    • SketchUp Resources
    • Bureaucratic Affairs Building HHW System Logic Exercise
    • Bureaucratic Affairs Building Scavenger Hunt
    • Chilled Water Plant System Diagram Exercise
    • The HIjend Hotel >
      • Chilled Water Plant Scoping Exercise
      • Ballroom AHU Scoping Exercise
      • Cooling Tower Scoping Exercise
  • Tools
    • Altitude Correction Factor
    • Economizer Evaluation Checklist
    • Eikon for Educators and WindLGC
    • Effective Duct Length Tool
    • Excel Third Axis Tool
    • Excel Time Value Conversion
    • Insulation Savings Tools
    • Logic Diagram Tool >
      • Logic Diagram Example - Discharge Air
      • Logic Diagram Example - CHW Plant 01
      • Logic Diagram Example - VAV AHU
    • Mixed Air Calculations
    • Monitoring Plan Spreadsheet
    • Pipe Friction Chart
    • Plot Digitizer >
      • Plot Digitizer Pump Curve Example
    • Square Law Spreadsheet
    • System Diagram Symbols
    • Thermodynamic Diagrams Spreadsheet
    • Universal Translator Data Analysis Tool
    • y = (m * x) + b Spreadsheet
  • Useful Formulas
    • Affinity Laws
    • Circular Equivalent Duct
    • Effective Duct Length
    • FT Guide Appendix C
    • HVAC Equations and Concepts
    • Hydraulic Diameter
    • Pump Power and Energy
    • "Square Law"
  • What's That Thing?
    • Cooling Towers
    • Pumps
    • Valves
  • Resources
    • Bill Coad's Writings
    • Data Logging Resources
    • EBCx Skills Guidebook
    • Energy Design Resources
    • Fisher Controls Valve Cavitation Bulletin
    • Functional Testing Guide
    • Honeywell Gray Manual
    • MCC Powers Bulletins
    • NBCIP Reports
    • PEC Tool Lending Library
    • PID Resources
    • Pneumatic Control Resources
    • Resource List
    • Scoping Resources
    • TAB Resources
    • Vintage Carrier Design Manual
    • VRF Systems
    • Williams' Wisdom
  • Videos
    • Bureaucratic Affairs HHW Logic Answers
    • Cooling Tower Flow Variation
    • Economizer Stratification
    • Functional Testing
    • Induction Principles
    • Monitoring Plans
    • CW Pump Deadheaded by Tower Lift
    • Ripple Effects
    • Testing a Pump
    • The Garden of Low Entropy
    • Variable Flow Systems
  • Training
    • Materials from Classes and Presentations >
      • ACEEE
      • ASHRAE
      • ASHRAE - Engineers Notebook
      • BCxA and NCBC
      • BEST Institute
      • Case Studies
      • ERDC 2020 RCx Academy
      • ELPNW
      • ICEBO
      • Marriott AEP
      • Magazine Articles
      • NAVFAC
      • Pacific Energy Center Design, Performance and Commissioning Issues Classes
      • Pacific Energy Center EBCx Project Review
      • Pacific Energy Center EBCx Workshop Series >
        • EBCx Workshop Series 12
        • EBCx Workshop Series 13
        • EBCx Workshop Series 14
        • EBCx Workshop Series 15 >
          • Student One On One Discussions
        • EBCx Workshop Series 16
        • EBCx Workshop Series 17
        • EBCx Workshop Series 18
      • Portland General Electric
      • U of W >
        • U of W Archive
    • On Demand Training >
      • Benchmarking UCA and Scoping
      • Loads and Psychrometrics
      • Induction Motor Principles
      • Introduction to Functional Testing
      • Scope of Work Documents
      • System Diagraming
    • Training Opportunities
  • Contact
    • Copyright and Permissions
  • Home
    • What's New
  • Blog
    • Blog Support
  • SketchUp Models
    • SketchUp Resources
    • Bureaucratic Affairs Building HHW System Logic Exercise
    • Bureaucratic Affairs Building Scavenger Hunt
    • Chilled Water Plant System Diagram Exercise
    • The HIjend Hotel >
      • Chilled Water Plant Scoping Exercise
      • Ballroom AHU Scoping Exercise
      • Cooling Tower Scoping Exercise
  • Tools
    • Altitude Correction Factor
    • Economizer Evaluation Checklist
    • Eikon for Educators and WindLGC
    • Effective Duct Length Tool
    • Excel Third Axis Tool
    • Excel Time Value Conversion
    • Insulation Savings Tools
    • Logic Diagram Tool >
      • Logic Diagram Example - Discharge Air
      • Logic Diagram Example - CHW Plant 01
      • Logic Diagram Example - VAV AHU
    • Mixed Air Calculations
    • Monitoring Plan Spreadsheet
    • Pipe Friction Chart
    • Plot Digitizer >
      • Plot Digitizer Pump Curve Example
    • Square Law Spreadsheet
    • System Diagram Symbols
    • Thermodynamic Diagrams Spreadsheet
    • Universal Translator Data Analysis Tool
    • y = (m * x) + b Spreadsheet
  • Useful Formulas
    • Affinity Laws
    • Circular Equivalent Duct
    • Effective Duct Length
    • FT Guide Appendix C
    • HVAC Equations and Concepts
    • Hydraulic Diameter
    • Pump Power and Energy
    • "Square Law"
  • What's That Thing?
    • Cooling Towers
    • Pumps
    • Valves
  • Resources
    • Bill Coad's Writings
    • Data Logging Resources
    • EBCx Skills Guidebook
    • Energy Design Resources
    • Fisher Controls Valve Cavitation Bulletin
    • Functional Testing Guide
    • Honeywell Gray Manual
    • MCC Powers Bulletins
    • NBCIP Reports
    • PEC Tool Lending Library
    • PID Resources
    • Pneumatic Control Resources
    • Resource List
    • Scoping Resources
    • TAB Resources
    • Vintage Carrier Design Manual
    • VRF Systems
    • Williams' Wisdom
  • Videos
    • Bureaucratic Affairs HHW Logic Answers
    • Cooling Tower Flow Variation
    • Economizer Stratification
    • Functional Testing
    • Induction Principles
    • Monitoring Plans
    • CW Pump Deadheaded by Tower Lift
    • Ripple Effects
    • Testing a Pump
    • The Garden of Low Entropy
    • Variable Flow Systems
  • Training
    • Materials from Classes and Presentations >
      • ACEEE
      • ASHRAE
      • ASHRAE - Engineers Notebook
      • BCxA and NCBC
      • BEST Institute
      • Case Studies
      • ERDC 2020 RCx Academy
      • ELPNW
      • ICEBO
      • Marriott AEP
      • Magazine Articles
      • NAVFAC
      • Pacific Energy Center Design, Performance and Commissioning Issues Classes
      • Pacific Energy Center EBCx Project Review
      • Pacific Energy Center EBCx Workshop Series >
        • EBCx Workshop Series 12
        • EBCx Workshop Series 13
        • EBCx Workshop Series 14
        • EBCx Workshop Series 15 >
          • Student One On One Discussions
        • EBCx Workshop Series 16
        • EBCx Workshop Series 17
        • EBCx Workshop Series 18
      • Portland General Electric
      • U of W >
        • U of W Archive
    • On Demand Training >
      • Benchmarking UCA and Scoping
      • Loads and Psychrometrics
      • Induction Motor Principles
      • Introduction to Functional Testing
      • Scope of Work Documents
      • System Diagraming
    • Training Opportunities
  • Contact
    • Copyright and Permissions

100% Effective Duct Length

Picture
 The concept of 100% effective duct length is an important one in the HVAC industry.   When air exits a fan, the flow profile is distorted by the action of the fan wheel flinging the air towards its perimeter, causing more air to be concentrated at the outside of the fan scroll and thus, a higher velocity at that location.  

​As the air moves down the duct, this distorted profile interacts with the duct wall, causing the faster air to slow down and the slower air to speed up.  In addition, some of the velocity pressure is converted to static pressure, a phenomenon called "regain".

The point in the system where a uniform velocity profile has re-established itself is called the 100% effective duct length.   If transitions or fittings are introduced into the fan discharge duct before the 100% effective duct length point, the fan performance will be adversely affected and the losses in the fittings will be higher than predicted by the loss coefficients, a phenomenon called System Effect. If you want  to know more about system effect, you may find the blog post titled 
System Effect–Dealing with the Point Where the Fan Meets the Duct to be helpful

Thus, it is desirable to be able to compute the 100% effective duct length and if at all possible, avoid placing any fittings between that point and the fan.  The formula for 100% effective duct length is as follows.
Picture
The download below will give you to the .wmf file that is discussed above so you can use it to document your math in a spreadsheet, report, or presentation.   You may also find the following related information on the website to be helpful:
  • As you may have observed, calculating effective duct length requires that you know the equivalent duct diameter if you are dealing with a rectangular duct.  You will find the AMCA equation for equivalent duct length here.  That page also contains some ASHRAE equations that have a similar sounding name but are a different concept and thus not interchangeable with the AMCA term in the Effective Length equation.
  • The Effective Duct Length spreadsheet tool has the equations for 100% effective duct length, equivalent diameter, circular equivalent of a rectangular and flat oval duct, and hydraulic diameter built into it to allow you to enter a flow rate and your duct dimensions and calculate the various metrics.
effective_duct_length.wmf
File Size: 16 kb
File Type: wmf
Download File

Home

Blog

Contact

Picture
A Field Perspective on Engineering - © 2017 Facility Dynamics Engineering, All Rights Reserved
(Contact Me to Check on Lefts or Any Other Questions You May Have about Permissions)