Definition and Function of Air Terminal Devices
2025-06-05
Definition
The Variable Air Volume Terminal Unit is the core component in a Variable Air Volume (VAV) air conditioning system, responsible for regulating the supply air volume. It achieves dynamic airflow control by adjusting the opening of air dampers or integrating with fans, precisely modulating supply air parameters in response to changes in indoor load conditions.
Pressure-independent: Operation remains unaffected by fluctuations in pipeline pressure, ensuring a consistent airflow output.
Structural classification includes single-airway types, series/parallel fan-powered types (FPB), dual-airway types, and more.
Core role
| Function | Implementation mechanism | Technical Highlights |
|---|---|---|
| Dynamic Load Response | Adjust the primary air volume based on the room temperature sensor's command, matching the real-time heating and cooling load. | The minimum airflow can be reduced to 35% of the design value. |
| Minimum airflow guarantee | Set mechanical constraints or control logic to ensure hygienic ventilation needs—such as CO₂ control—and meet airflow organization requirements. | Avoid completely closing the damper, which could lead to stagnant airflow. |
| System pressure is stable. | Limit the minimum airflow at the terminal units to reduce duct pressure fluctuations caused by multi-device adjustments. | Maintain the stability of other terminal air supply |
| Mixing and Reprocessing | Introduce a secondary return air mixing system (series-type FPB) or an integrated reheat module to optimize supply air temperature. | Secondary return air induction ratio n = 1.5–4 |
| Improved environmental quality | Optional air filter available to purify the incoming air. | Reduce particulate matter concentration |
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