In a single-duct constant-volume system, what parameter remains fixed regardless of load?

In a single-duct constant-volume system, what parameter remains fixed regardless of load?

• A. The flow to each space.
• B. The outdoor air fraction
• C. The return air temperature
• D. The humidity ratio

Answer: (A)

In a single-duct constant-volume system, the central unit delivers a fixed amount of supply air at a constant volume per unit time. The control strategy to meet varying space loads is to change the condition of that air (its temperature, and in some cases humidity) rather than the amount of air delivered. Therefore, the flow to each space remains fixed regardless of load. The outdoor air fraction, return air temperature, and humidity ratio can all change with load or operating conditions, but the supply air volume is constant by design.

In a single-duct constant-volume system, the central unit delivers a fixed amount of supply air at a constant volume per unit time. The control strategy to meet varying space loads is to change the condition of that air (its temperature, and in some cases humidity) rather than the amount of air delivered. Therefore, the flow to each space remains fixed regardless of load. The outdoor air fraction, return air temperature, and humidity ratio can all change with load or operating conditions, but the supply air volume is constant by design.