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| Published by the Air Conditioning Contractors of America (ACCA)
The Third Edition of ANSI/ACCA Manual D is the Air Conditioning Contractors of America procedure for sizing residential duct systems. This procedure uses Manual J (ANSI/ACCA, Eighth Edition) heating and cooling loads to determine space air delivery requirements. This procedure matches duct system resistance (pressure drop) to blower performance (as defined by manufacturer’s blower performance tables). This assures that appropriate air flow is delivered to all rooms and spaces; and that system air flow is compatible with the operating range of primary equipment. The capabilities and sensitivities of this procedure are compatible with single zone systems and multi-zone systems. The primary equipment may feature a multi-speed blower or a variable speed blower.
Design a residential duct system in less time with the streamlined Manual D duct procedure. The newly released Manual D has been significantly revised to include:
- Updated and expanded VAV guidance, with detailed examples.
- Impacts of excess length, sag and compression in flexible ducts.
- New equivalent length values for flex duct junction boxes.
Manual D provides:
- A single set of ANSI-recognized duct sizing principles and calculations that apply to all duct materials.
- System operating point (supply Cfm and external static pressure), and airway sizing for single-speed and multi-speed (ECM) blowers.
- A method for determining the impact of duct friction and fitting pressure drop on blower performance and air delivery.
- The most comprehensive equivalent length data ever published.
You can apply the Manual D procedure to constant volume systems and zoned variable air volume systems, over a full range of duct construction materials. Manual D includes a number of informative appendices related to air distribution systems (e.g., equipment and air-side components, controlling excess air when VAV dampers close, duct loads, duct leakage and duct system efficiency, air quality issues, noise control, minimum air velocity for ducts; codes, standards and best practice issues; and commissioning issues).
Overview
The Third Edition of Manual D (D3) designs duct systems for low-rise, residential-use buildings. This set excludes dwellings classified as Residential Group R (per Section 310 of the 2006 International Building Code), low-rise apartment buildings, and residential structures converted to commercial use. Use commercial procedures for institutional and high-rise construction.
Organization
Thirteen sections provide information, guidance, calculation tools, and examples relevant to the standard. The first five appendices provide charts, tables, look-up values, supporting detail, and guidance relevant to the standard. The last thirteen appendices provide informative guidance, detail and worksheets that are not part of the standard.
Obligatory Sections and Appendices
Obligatory sections and appendices are required reading (part of the ANSI Standard). Obligatory appendices provide requirements and calculation procedures for sizing residential duct system airways. Obligatory appendices provide implementation examples, explanations and related guidance.
Section 1 - Basic Duct Sizing Principles
Provides a brief summary of the Manual D procedure.
Section 2 - System Operating Point
Introduces the concept of the system operating point, as it applies to a multi-speed blower operating at one speed and at alternative speed settings.
Section 3 - Blowers
Expanded discussion of blower performance (variable speed, variable Cfm design; variable speed, con- stant Cfm design; altitude and temperature effects; inlet and discharge effects and noise).
Section 4 - System Performance Issues
Discusses the friction rate and pressure drop for straight duct, fitting performance, the standard of care for design and installation, and the pressure drop produced by air-side devices and equipment.
Section 5 - Prerequisites for Air Distribution System Design
Summarizes tasks that must be completed prior to using the Manual D procedure and their relationship to the duct sizing procedure.
Section 6 - Duct Sizing Calculations
General discussion of the components and sequence of the Manual D procedure.
Section 7 - Sizing Rigid Constant Volume Duct Systems
Application examples (constant volume, rigid duct material, rectangular and radial geometries).
Section 8 - Sizing Flexible Constant Volume Duct Systems
Application examples (constant volume, flexible duct material, rectangular and radial geometries).
Section 9 - Variable Volume Systems
General discussion of variable air volume system issues and design procedures (zoning and room temperature control, load calculation protocol, sizing system components, affects of changing air flow rates, affect on blower operating point, bypass duct and maintaining system air flow, affect on supply air outlet performance, sizing VAV dampers, hand dampers required for gross balancing, protocol for sizing airways).
Section 10 - Sizing Rigid Variable Volume Duct Systems
Application examples (zoned variable volume systems with and without cooling load diversity; rigid duct material, rectangular geometry).
Section 11 - Sizing Flexible Variable Volume Duct Systems
Application example (zoned variable volume system with cooling load diversity; flexible wire helix duct material, junction box geometry).
Section 12 - Sizing Two Zone Bi-level Duct Systems
Application example (two-zone variable volume system adjusts air flow to lower level and upper level to compensate for the buoyancy of warm air; each level has cooling load diversity; rigid duct material, rectangular geometry).
Section 13 - Sizing Variable Volume Retrofit Systems
Application example (variable volume dampers and control added to existing single zone constant volume system, space has cooling load diversity; rigid duct material, rectangular geometry).
Appendix 1 - Equations and Tables
Summary of commonly used equations; air velocity limits.
Appendix 2 - Friction Charts, Duct Slide Rules and Equivalency Tables
Friction charts summarize the performance of common duct materials; duct slide rules duplicate friction chart data; tables convert round airway size to rectangular airway size and vice versa.
Appendix 3 - Fitting Equivalent Lengths
Default equivalent length values for duct fittings (fitting pressure drops for 900 Fpm air velocity and a 0.08 IWC/100 Ft friction rate are converted to feet of straight duct that has equivalent air flow resistance).
Appendix 4 - Fitting Equivalent Length Adjustments
Alternative equivalent length values for duct fittings (fitting pressure drops for air velocities less than 900 Fpm and/or friction rates other than 0.08 IWC/100 Ft are converted to feet of straight duct that has equivalent air flow resistance).
Appendix 5 - Terminology
Definitions of terms used by Manual D.
Informative Appendices
Informative appendices are recommended reading (not part of the ACCA/ANSI Standard). Informative appendices provide references to related good practice and/or statutory requirements not covered by this standard (standards and codes that deal with design issues other than airway sizing, installation issues and commissioning issues). Informative appendices also provide general discussion of duct system issues, information and detail concerning certain aspects of this standard, and guidance pertaining to performance issues that are related to air delivery, but which do not affect air delivery.
Appendix 6 - Duct Construction Standards
Summary of codes and standards for fabricating and installing residential duct systems.
Appendix 7 - Standard of Care and Continuity
Recommended standard of care for installing duct systems and for making airway sizing calculations.
Appendix 8 - Residential Air Distribution Systems
Summary of zoning issues (a primary consideration for a successful design); overview of various types of duct systems and duct materials; guidance for selecting the type of duct system; reviews issues that affect duct location and duct fabrication.
Appendix 9 - Equipment and Air-Side Components
Introduces the types of primary equipment, secondary equipment and air-side devices used with residential duct systems.
Appendix 10 - Duct System Efficiency
Duct system efficiency (affect of airway shape, aspect ratio, duct material, heat transmission across duct walls and duct leakage); duct insulation issues, duct leakage issues, moisture and condensation issues, effect on applied cooling and heating efficiency ratings (EER and COP), affect on utility demand load.
Appendix 11 - Duct Leakage and System Interactions
Space pressure, infiltration, exfiltration, supply Cfm, return Cfm, combustion air and vent performance are affected by the tightness of the thermal envelope, the performance of the primary air moving equipment, the use of exhaust equipment, and by supply duct leakage and return duct leakage. Synergistic effects may produce unsafe or undesirable conditions in the occupied space.
Appendix 12 - Air Quality Issues
Brief discussion of indoor air quality issues.
Appendix 13 - Noise
Sources of noise and strategies for reducing or attenuating noise.
Appendix 14 - Testing and Balancing
Survey of testing and balancing issues and requirements.
Appendix 15 - Air Velocity for Ducts and Grilles
Discussion of the consequences of low air velocity through duct airways and supply air grilles, diffusers and registers.
Appendix 16 - Temperature Calculations for Bypass VAV System
Procedure for estimating discharge air temperature for heating and cooling when bypass air is mixed with return air.
Appendix 17 - Excess Length and Sag in Flexible Duct
Airway sizing adjustments for flexible wire helix duct does not comply with industry installation standards.
Appendix 18 - Symbols and Abbreviations
Appendix 19 - Manual D Worksheets
Worksheets for Manual D calculations.
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