Manual T - Air Distribution Basics

Manual TManual T - Air Distribution Basics

ACCA’s Manual T: Air Distribution Basics for Residential and Small Commercial Buildings provides detailed information on how to select, sizing, and locate constant volume supply out-lets and return inlets. Floor, low-side wall, high-side wall, and ceiling out-lets are also discussed.

Additionally, Manual T replaces all current and previous editions of ACCA Manual E: Room Air Distribution Considerations. Manual T contains all of the information previously provided in Manual E, with a considerable amount of additional information.


Manual T is divided into twelve sections with an additional two appendices for supplementary information.

Section 1 - What Makes People Comfortable
Section 1 begins with the importance of proper air terminal sizing and selection procedures and their relationship with how various factors affect human comfort.

  • Minimum Amount of Air Required for Survival
  • Amount of Air Required for Comfort
  • Metabolic Rate
  • Heat Transfer to the Surrounding
  • Effect of Surrounding Temperature
  • Building Envelopes Affects Human Comfort
  • Mean Radiant Temperature
  • Effect of Winter Humidification
  • Effect of Velocity
  • Natural Convection
  • ASHRAE Comfort Chart
  • Temperature Gradients

Section 2 - Air Distribution Concepts and Terminology
Section 2 goes over the terminology and design concepts associated with Air Distribution.

  • General Categories of Terminal Devices
  • Types of Ceiling Diffusers
  • Types of Floor Diffusers
  • Primary Air and Secondary Air
    • Throw
    • Drop
    • Rise
    • Surface Effect
    • Spread
  • Primary Air Pattern
  • Total Air Pattern
  • Entrained Air
  • Stagnate (or Stratified) Zone
  • Vertical Temperature Gradient
  • Gross Area
  • Free Area
  • Face Velocity
  • Core Velocity
  • Velocity / Flow-Rate Equation

Section 3 - High Sidewall Terminals
Section 3 goes over expected air patterns when working with high-sidewall terminals.

  • Location
  • Primary Air Pattern
  • Entrance Condition Affects the Air Pattern
  • Total Air Pattern
  • Stratification
  • Secondary Air Pattern
  • Use Vanes to Control Air Pattern
  • Characteristics of High Sidewall Registers
  • Location of Returns

Section 4 - Ceiling Diffusers
Section 4 goes over expected air patterns when working with ceiling terminals.

  • Primary Air Pattern, Radial Discharge
  • Primary Air Pattern, Directional Discharge
  • Primary Air Pattern, Vertical Discharge
  • Entrance Conditions Affect the Air Pattern
  • Total Air Pattern, Horizontal Discharge
  • Total Air Pattern, Vertical Discharge
  • Stratification, Horizontal Discharge
  • Stratification, (Vertical Discharge Diffusers)
  • Characteristics of Horizontal Discharge Outlets
  • Characteristics of Vertical Discharge Outlets
  • Location of Returns

Section 5 - Floor and Low Sidewall Outlets
Section 5 goes over expected air patterns when working with floor-mounted diffusers, low sidewall diffusers, floor registers, and low sidewall registers.

  • Primary Air Pattern, Vertical Diffuser
  • Primary Air Pattern, Vertical Registers
  • Primary Air Pattern, for Horizontal Discharge
  • Entrance Conditions Affect the Air Pattern
  • Total Air Pattern, (Vertical Discharge Diffusers)
  • Total Air Pattern, (Vertical Discharge Registers)
  • Total Air Pattern, (Horizontal Discharge Outlets)
  • Basement Heating
  • Stratification, (Vertical Discharge Diffusers)
  • Stratification, (Vertical Discharge Registers)
  • Stratification, (Horizontal Discharge Outlets)
  • Floor and Low Sidewall Outlet Characteristics
  • Location of Returns

Section 6 - Pressure Loss Characteristics of Supply Outlets
Section 6 details the nature and principles of pressure loss through supply outlets.

  • Inches of Water
  • Static Pressure
  • Total Pressure
  • Velocity Pressure
  • Static Regain
  • Pressure Loss with Constant Velocity
  • Pressure Loss with Changing Velocity
  • Pressure Loss of Supply Outlets
  • Accessory Pressure Loss
  • Optimum Outlet-Fitting Geometry

Section 7 - Performance of Return Inlets
Section 7 discusses the performance and importance of Return Inlets.

  • Types of Return Inlets
  • Negligible Effect on Room Air Patterns
  • Guidelines for Locating Returns

Section 8 - Pressure Loss Characteristics of Return Inlets
Section 8 discusses the pressure loss characteristics of Return Inlets.

  • Inlet Pressure Loss
  • Pressure Loss is Affected by Inlet Geometry

Section 9 - Sound Considerations
Section 9 details the sound considerations when working with air distribution systems.

  • Frequency
  • Sound Pressure
  • Sound Power
  • Frequency Spectrum
  • Loudness Chart
  • Noise Criteria Rating
  • Published NC Ratings
  • Acceptable NC for Various Applications
  • Face Velocity Guidelines
  • Catalog Velocity Recommendations
  • Installations Details Affect Noise Levels
  • Integral Dampers Generate Noise
  • Attenuations Generation
  • Equipment Near the Occupied Space

Section 10 - Selecting Supply Outlets
Section 10 covers the selection process when choosing a supply outlet.

  • Objectives
  • Location
  • Approximate Air Terminal CFM
  • Selection Procedure
  • Effect of Fan Operation
  • Noise Criteria
  • Manufacturer’s Data
  • Floor, Baseboard and Low Sidewall Outlets
  • Example: Floor on Baseboard Outlet Selection
  • Ceiling Diffusers
  • Example: Non Directional Ceiling Diffuser
  • Example: Direction Ceiling Diffuser
  • High Sidewall Outlets
  • Example: High Sidewall Outlet Selection

Section 11 - Selecting Return Inlets
Section 11 goes over the selection process when choosing return inlets.

  • Style and Location
  • Size
  • Pressure Drop
  • Transfer Grilles
  • Filter Gilles
  • Residential Example
  • Commercial Example
  • Transfer Grille Example

Section 12 - Balancing and Measuring Air Flow
Section 12 goes over the process of successfully balancing and measuring a system’s airflow.

  • Balancing Procedures
  • Area Factor

Appendix 1 - Manufacturer’s Application Data

Appendix 2 - Summary of Tables, Charts and Equations


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