HVAC Ducting - Principles and Fundamentals

A. Bhatia, B.E.

Course Outline

Ducts convey the conditioned air from your heating and cooling plant out through the building and return it back to be conditioned again.

A properly designed duct system is critical to the success of a HVAC system. Good duct design can result in first cost savings, substantial operating cost savings, and lower noise levels by minimizing and equalizing static pressure throughout the system. A ductwork system that is not properly designed, installed, insulated and sealed can increase total heating and cooling costs up to 40% and may decrease the comfort, health and safety of your facility.

The course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

At the conclusion of this course, the reader will:

• Describe the terminology used to describe the components of air distribution system;
• Learn the velocity and pressure classification of ductwork;
• Learn the application of various materials in selection of ductwork;
• Understand the ductwork shapes that provides most cost effective alternative;
• Learn the various supply air duct configurations;
• Understand the importance of return duct configurations in maintaining neutral pressure;
• Understand the various duct sizing methods;
• Learn the methods of duct construction and reinforcement;
• Understand the good engineering practices for duct layout and routing;
• Learn the ductwork design considerations and ductwork system effect;
• Learn the methods for ductwork testing and estimating system performance; and
• Learn the various duct cleaning methods.
  

Intended Audience

This course is aimed at Mechanical and HVAC engineers, Architects, Building designers, Energy Auditors, Facility managers, Property & Estate managers, Operational & Maintenance Personnel, Sales & Marketing personnel, and General Audience.

Course Introduction

A duct system is an assembly whose primary function is to convey air between specified points. Most residential and commercial building HVAC design is based on low to medium pressure systems.
A duct system may contain ducts under positive and negative pressure. Good duct design optimizes:

1) Duct size (manufacturing costs)
2) Duct systems pressure losses (operation cost)
3) Duct systems acoustics (environmental costs)
4) Air balance procedures (commissioning costs)

Ductwork should be designed using accepted engineering practice and data such as ASHRAE handbooks, Manual-D, published by the Air Conditioning Contractors of America (ACCA) and the SMACNA HVAC Duct Systems Design manual.


Course Content

The course content is in a PDF file HVAC Ducting - Principles and Fundamentals. You need to open or download this document to study this course.

Course Summary

Ductwork is the system of ducts and ductwork accessories that are used to connect air handling units and fans with the rooms, spaces, or exhaust hoods with which they are associated. The material used for a duct system must be based on the availability of the material, expertise of the duct installer, the type of duct already installed, the location of the installed duct, and the environment it is planned to be used in. For example, metallic ducts are usually built from sheets of aluminum or galvanized steel. The ducts may either be built with round or rectangular cross sections. Non-metallic ducts are usually built from fiberglass duct board, except for ducts handling corrosive fumes that are constructed from a PVC material. Fiberglass duct board sheets are generally in locations where the duct will not be damaged by objects or personnel.

With the many available systems-sizing methods (equal friction, static regain, velocity reduction, total pressure) and system types, performance cannot be economically optimized unless the designer selects construction details appropriate for the given pressure and velocity. Most designers use the constant friction gradient. Generally speaking, duct strength, deflection and leakage are more functions of pressure than of velocity. In conventional systems, noise, vibration and friction loss are more related to velocity than to pressure.

Besides meeting the desired sizing constraints, an HVAC duct system should be routed so as to minimize the individual lengths of the various duct runs. Optimally routing duct work minimizes material costs and helps to create a naturally balanced system where the static pressure and air velocities available at each diffuser are as similar as possible. An intelligent placement of the air handler and routing the ductwork is an art that can minimize the pressure losses and air velocities.

All joints should be sealed with a special pressure-sensitive tape made for this purpose; standard duct tape should not be used. Duct insulation helps prevent the warming of your chilled air and the cooling of your heated air as it passes through the ducts. 1 inch thick insulation is typically the required minimum for ducts carrying hot or cold air. Proper choice of insulation can also help reduce the transmission of noise from your HVAC system to the working spaces inside your building.

Ducts can be best described as arteries of the central air-conditioning system. Good duct design is key element in keeping the whole HVAC system fit and achieving comfortable conditions through out its life span.

Quiz

Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

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DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.

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