Manual J® (8th Edition) is the ANSI-recognized standard for determining the heating and cooling loads for residences to install the right size of HVAC equipment. It applies to all sorts of residential buildings, from single-family dwellings to apartment buildings. Compliance is often a must in building codes. The 8th edition has some key changes from the previous version, for example, there is a new normative section that defines the requirements, some clarifications on design conditions and adjustable defaults, a software interpolation rule, greater detail on certain aspects such as ventilation, and modified worksheets and appendices. The manual is divided into informational parts that describe basic and advanced calculations, procedures, and tables, and the only mandatory normative part. The following is a summary of the changes made and the structure of the document; for detailed information and instructions, please refer to the manual.
ACCA - Manual J
Some of the key revisions made in the 8th Edition as compared to the 2011 (v2.11) edition are as follows:
• Section N (Normative Requirements): This new section defines the load calculations to be done using the Cooling Load Factor/Cooling Load Temperature Difference (CLF/CLTD) method for code purposes. It also mandates the documentation of the existence of Adequate Exposure Diversity (AED).
• Design Conditions: The 8th Edition has also made some provisions on the permissible sources of design conditions and these include using the values in Manual J Table 1A/1B or weather data from ASHRAE and forbidden the combination of these data sources.
• Adjustable Defaults (Figure 3-1): This figure has been expanded to provide more comprehensive guidance on the appropriate use of default values for various building components such as windows, skylights, insect screens, surface reflectiveness, opaque panels, encapsulated attics, infiltration rates, duct load factors, and moisture migration.
• Software Interpolation: A specific rule regarding software interpolation has been introduced. Interpolation is necessary when the rounding of the values of the variables results in a difference of more than 5% when compared to the fully interpolated result.
• Section 3 Enhancements: Section 3 has been updated to provide more specific guidance on several topics, such as engineered ventilation (treated as both a system load and a space load), kitchen range hoods, and fireplaces and space heating stoves.
3A-2 (Heat absorbing glass – windows)
3A-3 (Reflective glass – windows)
3C-2 (Flat heat absorbing glass – skylights)
3C-3 (Flat reflective glass – skylights)
3C-5 (Tinted plastic dome - skylights)
3C-6 (Milky plastic dome – skylights)
3E-2 (Latitude adjustment for generic fenestration)
3E-4 (SHGC values for light and dark shading devices used with generic fenestration)
8B (Moisture content of sea level air)
• Table Deletions: Some of the tables that were related to fenestration properties and moisture content have been erased. For the list of deleted tables, please refer to the Table Deletion Notice within the manual.
• Worksheet Updates: Some changes have been made in the Worksheets E (Infiltration Loads), GS (Duct Runs in Unconditioned Space), and H (Ventilation Loads) to the current recommendations.
• Appendix Modifications: The appendices have been revised, Appendix 13 (ANSI ASHRAE Standard 62.2) has been removed and three new appendices have been added: Load calculations for energy efficient homes (Appendix 13), Manual J duct loads for duct leakage test specifications (Appendix 14) and Load calculations for large multifamily dwellings (Appendix 15).
Appendix 13 (ANSI ASHRAE Standard 62.2) in the 2011 Manual J has been deleted
New Appendix 13 (Load Calculations for Energy Efficient Homes)
New Appendix 14 (MJ8 Duct Loads for a Duct Leakage Test Specification)
New Appendix 15 (Load Calculations for Large Multifamily Dwellings)
The structure of Manual J 8th Edition manual is divided into five informative parts and one normative section:
Normative Section:
Section N: Normative Requirements
Informative Sections:
Part 1: Core Training (Basic Calculations). Sections 1-10, which present the basics and work through examples.
Section 1 - Types of Heating and Cooling Loads
Section 2 - Making an Accurate Load Estimate
Section 3 - Important Issues and Concepts
Section 4 - Component Heating Loads
Section 5 - Component Cooling Loads
Section 6 - Instructions for Using Form J1AE and the MJ8AE Worksheets
Section 7 - Vatilo Residence - Block Load
Section 8 - Victor Residence - Block Load
Section 9 - Long Residence - Block and Room Loads
Section 10 - What to Do Next
Part 2: For Instructors & Software Users (Advanced Calculations): Sections 11-17, which discuss further computations and present numerical examples.
Section 11 - Issues and Concepts
Section 12 - Smith Residence - Single Family Detached Example
Section 13 - Walker Residence - Single Family Detached Example
Section 14 - Cobb Residence - Inadequate Exposure Diversity
Section 15 - Bell Residence - Multi Zone System
Section 16 - Home Addition with Large South Glass Area
Section 17 - Solarium Heat Transfer Multipliers
Part 3: Detailed Procedures (Reference for Instructors & Programmers): Sections 18-28, which provide a more comprehensive discussion of the processes and technical aspects.
Section 18 - Design Conditions
Section 19 - Fenestration Load Procedures
Section 20 - Opaque Panel Load Procedures
Section 21 - Infiltration Load Procedures / Infiltration Principles
Section 22 - Internal Load Procedures
Section 23 - Duct Load Procedures
Section 24 - Ventilation Load Procedures
Section 25 - Blower Heat
Section 26 - Hot Water Piping Load
Section 27 - Winter Humidification Load
Section 28 - Moisture Migration Load
Part 4: Normative Tables (Weather & Building Component Data)
Part 5: Documentation & Guidance: Appendices 1-15, which include additional information, forms, and worksheets.
Appendix 1 - Notes for Instructors
Appendix 2 - MJ8AE Capabilities and Sensitivities
Appendix 3 - Adequate Exposure Diversity and System Compatibility
Appendix 4 - Physical Principles and Mathematics
Appendix 5 - Survey
Appendix 6 - Troubleshooting System Design Problems
Appendix 7 - Summary of Equations
Appendix 8 - Glossary
Appendix 9 - Symbols and Abbreviations
Appendix 10 - Forms and Worksheets
Appendix 11 - Software Protocol for Fenestration Loads
Appendix 12 - Software Protocol for Tables 4A and 4B
Appendix 13 - Load Calculations for Energy Efficient Homes
Appendix 14 - Manual J 8th Edition Duct Loads for a Duct Leakage Test Specification
Appendix 15 - Load Calculations for Large Multifamily Dwellings
This document provides a high-level summary. Users are directed to the complete ACCA Manual J 8th Edition for comprehensive information and specific instructions.