Print this page HVAC Design Overview of Variable Air Volume Systems
A. Bhatia, B.E.
Course Outline
Variable Air Volume systems or "VAV" is a general term for a type of HVAC system that supplies only the amount of air needed to satisfy the load requirements and can supply different volumes to different zones at the same time. The result is that the total supply of cool or warm air changes over the course of the day, depending on the heat gains or heat loss at different times.
This 4 - hour course
outlines the basic fundamentals for the design of Variable Air Volume system.
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 understand:
- How do variable air volume systems operate?
- What are the advantages and design challenges in incorporating VAV systems?
- What are the appropriate and inappropriate usages of VAV systems?
- What are different types of terminal outlets and describe why some work better than others?
- How do pressure-dependent systems compare with pressure-independent systems?
- What are the different types of control mechanisms applicable to VAV systems?
- How is outdoor air ventilation maintained with VAV systems?What are the various control loop options applicable to VAV systems?
- What do the terms Dumping, Coanda effect and ADPI mean?
- Why the variable speed drive provides energy efficient operation?
- Why the duct sizing for VAV systems is designed by static regain principle?
- Learn the rule
of thumb parameters applicable to VAV system.
Intended Audience
This course is aimed at HVAC designers, building services engineers, facility personnel, end users, service technicians, architects, maintenance supervisors, contractors, energy auditors, layout professionals and general audience.
Course Introduction
The HVAC air distribution systems are broadly classified as (1) the constant air volume systems and (2) the variable air volume systems. In a constant volume system the volume of air is held constant while the temperature is varied to meet the changing load conditions. In a VAV system, the volume of constant temperature air modulates to meet the changing load conditions.
The simplest VAV system incorporates one supply duct that, when in cooling mode, distributes approximately 55 degree F supply air. Because the supply air temperature, in this simplest of VAV systems, is constant, the air flow rate must vary to meet the rising and falling heat gains or losses within the thermal zone served. The air flow rate control is provided via two techniques; for single zone systems the blower's flow rate is varied. For a single VAV air handler that serves multiple thermal zones, the flow rate to each zone must be varied as well.
The popularity of VAV systems has grown rapidly due to their ability to save large amounts of heating, cooling and fan energy when compared to other HVAC systems. However, systems do not always work as they should and this could be due to any number of reasons. In almost all cases, problems and complaints result from errors or omissions in the design, construction and operation of the system and these can and should be corrected.
This course will
focus on the design challenges involving variable air volume systems.
Course
Content
The course content is in a PDF file HVAC Design Overview of Variable Air Volume Systems.
Please click on the above underlined hypertext to view, download or print the document for your study. Because of the large file size, we recommend that you first save the file to your computer by right clicking the mouse and choosing "Save Target As ...", and then open the file in Adobe Acrobat Reader. If you still experience any difficulty in downloading or opening this file, you may need to close some applications or reboot your computer to free up some memory.
Course Summary
In a VAV system, a central supply fan sends air through medium pressure ductwork to terminal units (VAV boxes) throughout the building. The airflow to each zone - a space or group of similar spaces - is controlled by the VAV box (a "smart damper"), which varies the airflow in response to the space temperature. As cooling loads in the zone drop, the damper continues to close until it reaches a minimum position. The minimum position provides the occupants of the zone with adequate ventilation air.
Variable Air Volume technology is the most viable technology in today's modern buildings both for energy efficiency and performance. The VAV boxes can be preconfigured with Building Automation System, which allows the facility manager to:
- Display all the zone temperatures in an area on a graphic
- Adjust the individual set-points of zones from a central location
- Maintain historical
records of zone temperature values.
A good understanding
of the Variable Air Volume (VAV) systems is essential for HVAC designer to meet
the needs of current fast track projects and at the same time ensure that the
building gets the environmental system that will best fit its needs.
Quiz
Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.
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.
