VARIABLE AIR VOLUME SYSTEM

VARIABLE AIR VOLUME SYSTEM

INTRODUCTION:


While the most important function of any variable air volume (VAV) system is to provide a high quality environment for building occupants, this critical function rarely receives the attention it deserves. As a result, basic control strategies for terminal VAV boxes have seen little significant change since the introduction of pressure independent box control more than 30 years ago.

However, by applying more effective operating strategies available with modern digital controls, designer can offer enormous improvements in building comfort and occupant control enhancement that will improve the comfort and climate in commercial buildings.

DISCRIPTION:

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 airflow 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:

• Shutoff
• VAV Reheat
• Parallel Fan Powered
• Series Fan Powered
• Dual Duct
• Changeover/Bypass


for more info visit.
http://www.enjineer.com/forum