What is the design objective of a single duct variable volume system?

• A. Maintain constant supply temperature regardless of load.
• B. Always maximize outside air intake.
• C. Vary supply volume to space in response to dry bulb thermostat.
• D. Operate with no reheat capability.

Answer: (C)

The design objective is to vary the amount of conditioned air delivered to each space to match the changing cooling/heating loads. In a single-duct VAV setup, one air handler serves multiple zones, and each zone’s VAV box modulates its damper to increase or decrease airflow based on the space thermostat (typically sensing dry-bulb temperature). By adjusting the supply air volume rather than forcing a fixed amount of air, the system can keep the space at its setpoint efficiently as loads rise and fall. The temperature of the supply air itself is not the primary control variable, and reheat or outdoor air considerations are secondary to meeting the zone load through volume control.