HVAC - Air Side: Variable Air Volume (VAV) Systems

SKU: RVI-11460Duration: 20 Minutes

How can you increase the efficiency of an HVAC system? The purpose of Heating, Ventilation and Air Conditioning (HVAC) systems is to provide environments that are comfortable for people and that allow equipment to operate safely and reliably. This interactive online course focuses primarily on the terminal units, or VAVs that increase the efficiency and add flexibility to an HVAC system.

Course Details


Training Time: 20 minutes

Compatibility: Desktop, Tablet, Phone

Based on: Industry Standards and Best Practices

Languages: English

Learning Objectives

  • Describe why HVAC zoning is required
  • Describe the principle behind Variable Air Volume (VAV) systems
  • Describe series fan powered VAV box operation
  • Describe parallel fan powered VAV box operation

Key Questions

The following key questions are answered in this module:

What is the purpose of HVAC systems?
The purpose of HVAC systems is to provide environments that are comfortable for people and that allow equipment to operate safely and reliably.

Why are HVAC zones needed?
As the spaces served by HVAC systems become larger and the thermal requirements become more diverse, simple air handlers and control systems are inadequate to handle the challenge.

What are Variable Air Volume systems?
In Variable Air Volume systems, a single air stream at a constant temperature from the air handler is supplied to a terminal unit, also known as a VAV box.

What are the two types of FPUs?
The two types of FPUs are series-flow and parallel-flow boxes.

When are fan powered units typically used?
Fan powered units are typically used in building perimeter zones and other locations where the thermal loads are more variable.

Sample Video Transcript

Below is a transcript of the video sample provided for this module:

A slight variation on the basic single duct VAV box is the bypass terminal. In this design, as the damper closes it restricts the flow of outlet air into the space but does not restrict the total incoming primary airflow. The difference between the incoming and outgoing flow is diverted, or bypassed, into a return plenum or duct. This approach has a lower initial cost, and achieves the goal using a variable airflow to control zone temperature. However, it does not achieve the energy savings of a true VAV system. Bypassing conditioned air represents a loss of energy. The bypass terminal is used when there is need to maintain a constant supply airflow through the air handler, for example to prevent freezing at an evaporator coil that is being used for humidity control. Some VAV boxes have a reheating unit in them. This consists of either a steam or hot water coil or an electric heater in the outlet airstream. These are typically used in the perimeter zones of buildings and in other places where supplemental heat is required. When heat is required from the terminal, the airflow is reduced to a predetermined minimum to minimize the reheating of incoming supply air. The temperature of the discharge air is then controlled by controlling the flow of hot water to a coil, or the current flow to an electric heater.
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