What is a Industrial Application Variable Air Volume (VAV) Variable Air Volume Controller Controller?

How does it work? Temperatures The Variable Air Volume A VAV system maintains the air VAV systems are most easily (VAV) controller is an supply at a constant temperature understood by first considering them electronic device for while individual zone thermostats as cooling applications. As the zone digital control of single vary the flow of air to each space temperature increases and if the Air duct, dual duct, fan maintaining the desired zone Handling Unit is supplying cool air, powered, and supply/ temperature. This is unlike a constant the VAV controller opens the VAV exhaust VAV terminal volume system that maintains a box damper to allow more cool air to configurations. constant volume of airflow to the reach the space. space, but varies the temperature of Along with the control the air stream in response to space The specific amount of air volume capability of the VAV temperature changes. VAV systems required to maintain a particular zone box, the controller are predominantly single duct, but temperature setpoint is dictated by can also integrate the about 15% are dual duct designs. the size of the space and the internal control of the room or and external heat loads. zone baseboard heat Air Handling System and lighting logic. In addition, since the size of the VAV The air handling system typically box dictates its maximum cooling maintains about 1 inch W.C. static capacity, a VAV box’s performance pressure inside the longest run of is dependent upon the mechanical duct work away from the supply fan. engineer’s correct box sizing for This ensures that each VAV terminal each zone. unit has enough pressure at its inlet to deliver the maximum required flow If the installed unit is too small, of air into the space. As each VAV insufficient cooling results and at box opens and closes in response high flow rates audible noise may to the temperature changes in the be emitted. If the installed unit space, the static pressure in the air is too large, proper control may handling system changes. It is the be difficult to attain since a small job of the controller at the air handler change in damper position causes to modulate the supply fan providing an excessive change in airflow. the needed amount of airflow to each VAV box by maintaining the static pressure setpoint. www.kavlico.com Tubing running from the Differential Where are pressure sensors used on a Pressure Sensor to the Upstream (High) and Downstream (Low) VAV Controller? Manifolds The above mentioned setpoint is used by the airflow loop, which samples airflow via a Differential Pressure Sensor (DPS) in the box inlet and modulates the damper to control the flow. Thus, the VAV box flow is independent of duct static pressure. The sensor is self is located outside of the duct in close proximity to the other electronics controls. Tubing is ran from the DPS to the manifolds on the high side which face upstream and the low side ports which face downstream.

Differential Pressure Sensor Product Series Recommendations In most applications the sensor is P992, P993, P1K and P1J mounted on the panel wall for ease of replacement but can be installed on the printed circuit board.

What the Air Flow Pickup Measures?

Downstream Air Flow Sensing Downstream Port Sensing Port

Static Pressure

Total Pressure

Static Pressure Area of Increased Velocity and Pickup High Pickup Low Decreased Pressure Manifold Pressure Manifold Pressure Duct Wall

Please note that these are just recommendations based on current applications. A thorough review by the end customer must be performed to determine the suitability of the product within their application.

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