NCIDQ IDFX Practice Exam

What is typically used to control air flow in a VAV system?

1. Gravity-fed ducts

2. Variable air volume boxes

3. Fixed duct openings

4. Manual impellers

The correct answer is: Variable air volume boxes

In a Variable Air Volume (VAV) system, Variable Air Volume boxes are key components used to control the flow of air. These boxes modulate airflow to different areas based on the specific heating and cooling needs of the space. By adjusting the volume of air delivered, VAV boxes can maintain comfort levels more efficiently compared to constant air volume systems. VAV boxes are designed with dampers that open or close in response to temperature sensors and the overall demand for heating or cooling within a space. This modulation not only helps maintain desired environmental conditions but also supports energy efficiency, as the system does not operate at full capacity when it's unnecessary. The other options do not effectively address the dynamic control of airflow in a VAV system. Gravity-fed ducts primarily rely on gravity to facilitate airflow without the need for mechanical modulation, which is not sufficient for the precise control required in a VAV system. Fixed duct openings do not allow for adjustment and can result in inefficient airflow management. Manual impellers may provide some level of control, but they do not offer the automated and responsive operation that VAV systems are designed to provide. Hence, the use of Variable Air Volume boxes is fundamental to the effective functioning of VAV systems.