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Glass &Windows Selection

VAV systems

VAV systems are designed to supply only the volume of conditioned air to a space that is needed to satisfy the load. Fan energy is saved when the volume of air handled by the fan is reduced. Air volume control is accomplished by installing modulating dampers, or in some cases, an air valve, in the supply duct to each zone. As the room temperature demand becomes satisfied, the thermostat signals the damper to move the supply air zone valve toward the closed position.

When zone valves are throttled, the static pressure in the supply duct changes. A static pressure sensor located in the supply duct senses the static pressure change, and either increases or decreases the airflow from the source, using variable speed control or dampers on the main air supply fan.

A key component in the VAV system is the air valve. It is commonly installed inside an insulated sheet metal box suspended in a ceiling plenum. The air valve has a damper that regulates the air flow in response to the room's thermostat. A multi-port pressure sensing ring provides both accurate airflow sensing and control in response to duct static pressure.

As VAV systems have evolved, so have the terminals. There are six popular VAV systems. They are:


VAV Reheat

Parallel Fan Powered

Series Fan Powered

Dual Duct


There are many different types of vav units:

Single Duct
Dual Duct
Fan Powered
Series Fan
VAV boxes can also be classified as pressure independent and pressure dependent. A pressure independent VAV measures cfm and will maintain the proper airflow regardless of the box inlet static pressure provided by the main air handling unit. A pressure dependent VAV does not measure airflow. The cfm will change depending on the inlet static pressure. VAV systems are also usually designed with a diversity factor which means that the main air handler design airflow is less than the sum of the total airflow of all the VAV's. This is a common design because not all of the VAV's in a building will be in full cooling or maximum cfm all at once. There are three ways that a VAV can be controlled; pheumatic, electric, or Automated Control Systems (ACS). Pneumatic control systems are becoming obsolete. The VAV damper is opened and closed by a controller sending air pressure to an actuator hooked to the VAV damper. Electric simply sends a signal from the thermostat in volts to an electric motor connected to the VAV damper. ACS works the same as electric except there is a main computer set up in the building that gets information from all the VAV's and air handlers displaying it in text and graphics form. The possibilities are endless with automated controls and is truly a huge leap forward in the HVAC industry.



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