Manual Q - Low Pressure, Low Velocity Duct System Design

Manual QManual Q - Low Pressure, Low Velocity Duct System Design

ACCA’s Manual Q: Low Pressure, Low Velocity, Duct System Design serves as a comprehensive guide for designing commercial, low velocity, low-pressure air distribution systems. This Manual provides time-saving, quick-fitting loss tables and a complete set of fitting loss tables compiled from the ASHRAE and SMACNA handbooks.

Additionally, Manual Q replaces all current and previous editions of ACCA Manual Q: Equipment Selection and System Design Procedures for Commercial Summer and Winter Air Conditioning.

PURCHASE MANUAL Q

Manual Q is divided into twenty-one informative sections, with an additional nine appendices for supplementary information.

Section 1 - Duct System Classification
Section 1 begins by classifying duct systems by function, path geometry, velocity range, pressure class, construction material, and class.

  • Classifications
    • Function
    • Paths
    • Velocity
    • Pressure
    • Materials
    • Shape

Section 2 - Duct System Requirements and Design Parameters
Section 2 covers the intricate system requirements, equipment requirements, and design parameters required for HVAC Duct System installations.

  • Classifications
  • Duct System Design Parameters
  • Architectural Considerations
  • Construction Costs and Operating Costs

Section 3 - Basics
Section 3 discusses some basic duct system principles and equations.

  • Flow and Pressure Equations
  • Duct Pressure Measurement Units
  • Duct Pressures - Total, Static and Velocity
  • Frictionless Regain and Conversion
  • Affect of Friction on Duct Pressure
  • Affect of Friction on Regain and Conversion
  • Pressure Measurement
  • Fan Performance Curves
  • Duct System Curves
  • Operating Point
  • Friction Charts and Duct Sizing Slide Rules
  • Correction for Duct Material
  • Altitude and Temperature Corrections
  • Duct Performance - Non-Standard Air
  • Fan Performance - Non-Standard Air
  • Operating Point - Non-Standard Air
  • Correction for Shape
  • Equal Friction Shape Conversion
  • Hydraulic Diameter

Section 4 - Duct System Pressure Changes
Section 4 goes over the duct system pressure changes, pressure loss, and pressure drops, and what component may be responsible for a pressure change.

  • Duct System Pressure Loss
  • Straight Section Pressure Drop
  • Fitting Pressure Drop
  • Fan Inlet and Outlet Pressure Drop
  • Airside Device Pressure Drop
  • Supply Outlet and Return Inlet Pressure Drop
  • Example of Duct System Pressure Changes
  • Duct System Total Pressure Drop
  • Duct System Static Pressure Drop

Section 5 - Fitting Losses
Section 5 details friction losses based on various aspects of the duct system.

  • Fitting Friction Loss
  • Fitting Dynamic Loss
  • Equivalent Length
  • General Comments on Fitting Design
  • Dynamic Loss Coefficient
  • Examples
    • Elbow Loss
    • Branch Take-off Fitting Loss
    • Diverging Flow Transitions
    • Converging Flow Transitions
    • Discharge into a Plenum
    • Exit from a Plenum
    • Offsets

Section 6 - Fan and Duct System Interface
Section 6 provides a general discussion of the “system effect” and its relation to various types of fan outlets and inlet configurations.

  • System Effect 
  • Fan Performance Tables
  • Field Performance
  • Effective Duct
  • Ideal Return
  • Loss Coefficients
  • Density Correction

Section 7 - Fan Outlet System Effects Losses
Section 7 details the system losses when a duct is not 100% effective.

  • System Effect at Fan Discharge
  • Blast Area and Outlet Area
  • Fan Discharge
    • Into Open Space
    • Into a Plenum
    • Into Elbow
    • Into an Outlet Diffuser
  • Fan Discharge Volume Control Dampers
  • Fan Discharge into Tees and Branch Take-offs
  • Air-Handler Cabinet Discharge Connections

Section 8 - Fan Inlet System Effect Losses
Section 8 discusses potential procedures that can be used to estimate how system factors affect pressure losses.

  • System Effect at Fan Inlet
  • Inlet Area
  • Non-ducted Inlets
  • Ducted Inlets
  • Fan Inlet Elbows
  • Documented Inlet Elbow Loss Coefficients
  • Undocumented Inlet Elbow Loss Coefficients
  • Fans Located in Plenums or Cabinets
  • Inlet Obstructions

Section 9 - Air Side Devices 
Section 9 categorizes various types of airside devices and provides information about their performance characteristics.

  • Pressure Loss Data
  • Velocity
  • Filters
  • Dampers
  • Louvers, Penthouses, and Hoods
  • Coils
  • Supply Air Outlets and Return Inlets
  • Air Distribution Devices
  • Humidifiers
  • Energy Recovery Equipment
  • Miscellaneous Equipment

Section 10 - Duct Sizing Methods
Section 10 goes over the various methods for duct sizing and fan selection.

  • Equal Friction Method
  • Modified Equal Friction Method
  • Extended Plenum Method
  • Semi-extended Plenum Method
  • Static Regain Method
  • Constant Velocity Method
  • Velocity Reduction Method

Section 11 - Duct System Design Procedure
Section 11 discusses components to consider when beginning the duct design process.

  • Design CFM Values
  • Select and Locate Air Distribution Devices
  • Locate the Central Equipment
  • Preliminary Layout
  • Sizing Calculations
  • Calculate the System Total Pressure Loss
  • Select the Fan
  • Noise
  • Final Drawings and Specifications

Section 12 - Example, Constant Volume System
Section 12 showcases examples of Constant Volume Systems in a variety of different commercial buildings.

  • Design Friction Rate for the Supply Ducts
  • Supply Duct Runs
    • A1to J
    • A1 to M
    • A1 to P
  • Return Duct Friction Rate and Pressure Loss
  • Return Duct Runs
    • T to Z1
    • X to W
  • Summary

Section 13 - Examples of VAV Designs
Section 13 showcases examples of how to design an air distribution system for modulating and dumping VAV systems.

  • Modulating VAV Systems
  • Example Problem, Modulating VAV Systems
  • Dumping VAV Systems
  • Examples Problem, Dumping VAV Systems

Section 14 - Application of Selected Types of VAV Equipment
Section 14 discusses how to design systems that utilize self-powered VAV diffusers and fan-powered VAV boxes.

  • Self-Powered VAV Supply Diffusers
  • Examples, Self-Powered VAV Diffusers
  • Fan-Powered VAV Box
  • Examples, Fan-Powered VAV Box

Section 15 - VVT, Rooftop Multizone, Radial and Flexible Duct Systems
Section 15 goes over design considerations that are specific to VVT systems, rooftop multizone systems, radial systems, and flexible duct/junction box systems.

  • VVT Systems
  • Designing the CO/BP-VAV System
  • Rooftop Multizone System
  • Designing the Rooftop Multizone Duct System
  • Radial Duct Systems
  • Designing the Radial Duct System
  • Flexible Duct - Junction Box Systems
  • Designing the Flexible Duct System

Section 16 - Fans
Section 16 provides detailed information regarding the design, performance, and application of different types of centrifugal and axial fans.

  • Fans
  • Definitions
  • Fan Types
    • Centrifugal Fans
    • Axial Fans
  • Fan Laws
  • Fan Control
  • Fan Economics
  • Factors that Affect Fan Selection
  • Fan Specification
  • Series and Parallel Fans
  • Standards

Section 17 - Building Pressure
Section 17 goes into detail about building pressure and considerations during the design process.

  • Room Air Balance
  • Economizer Cycle
  • Single Fan System
  • Supply Fan and Return Fan System
  • Supply Fan and Exhaust Fan System
  • Intake Openings
  • Control Dampers
  • Mixing Boxes and Stratification

Section 18 - Exhaust Air Systems
Section 18 discusses three broad categories of exhaust air systems, including human comfort, health and safety, and material handling systems.

  • Comfort Conditioning Exhaust Requirements
  • Exhaust System Applications
  • Codes and Regulations
  • Air Balance
  • Make-up Air
  • Toilet, Locker, and Shower Exhaust Systems
  • Kitchen Exhaust Systems
  • Non-ducted Exhaust Systems
  • Industrial Exhaust Systems

Section 19 - Provisions for Testing and Balancing the System
Section 19 details procedures and provisions for testing and balancing newly installed systems.

  • Design and Installation Affect the At&B Work
  • Balancing Dampers Required
  • Make Provisions for Performing the Balancing Work
  • Document the Design

Section 20 - Duct Insulation and Duct Leakage
Section 20 talks about the dangers and preventional measures against duct leakage.

  • Recommended Insulation Levels
  • Effective R-Values for Various Materials
  • Estimating Duct Wall Conduction Losses
  • Vapor Barries
  • Duct Sealing Requirements
  • Duct Leakage

Section 21 - Noise
Section 21 discusses noise and what it means for the HVAC system

  • Frequency
  • Sound Pressure
  • Decibel
  • Sound Power
  • Frequency Spectrum
  • Octave Bands
  • Loudness Chart
  • Noise Criteria Rating
  • Acceptable NC for Various Applications
  • Sound Meters
  • Equipment Performance Data
  • Sones and Phones
  • Attenuation
  • Regenerated Noise
  • Room Absorption Effect
  • Breakout Noise
  • Transmission and Transmission Loss
  • Crossstalk
  • Vibration Isolation
  • Designing for Noise Control

Appendix 1 - Equations

Appendix 2 - Friction Charts

Appendix 3 - Charts and Design Data

Appendix 4 - Device Pressure Drop and Performance Data

Appendix 5 - System Effect Loss Coefficients

Appendix 6 - Fitting Loss Coefficients

Appendix 7 - Drawing Standards

Appendix 8 - Guidelines and Checklists

Appendix 9 - “Quick" Fitting Tables

PURCHASE MANUAL Q


« Back to all Technical Manuals

Get connected to your National HVACR Community.

ACCA Membership gives you access to a wide variety of exclusive HVAC resources, including hundreds of hours of exclusive webinars, informational videos, access to downloadable templates, articles, and customizable marketing materials.

Learn more about becoming an ACCA Member »

become an acca member

And Get Member Exclusives

learn more

PLUS It's Risk-Free!

Connect with ACCA

Corporate Partners