What is the main difference between open-loop and closed-loop control in HVAC systems?

What is the main difference between open-loop and closed-loop control in HVAC systems?

• A. Open-loop has no feedback to correct performance; closed-loop uses sensor feedback to adjust actuators toward the setpoint.
• B. Open-loop uses sensor feedback to correct performance; closed-loop has no feedback.
• C. Open-loop and closed-loop are the same in terms of feedback.
• D. Closed-loop eliminates the need for sensors.

Answer: (A)

The idea being tested is how feedback distinguishes open-loop from closed-loop control in HVAC. In an open-loop system, commands are sent to equipment without checking the actual outcome—there’s no measurement to compare against a target. So you might set a heater or damper to a fixed action, and disturbances like a door opening or more people in the room won’t be automatically corrected. In a closed-loop system, sensors continuously measure the actual condition (such as room temperature), compare it to the desired setpoint, and adjust the actuators to reduce the difference. This feedback lets the system track the target and compensate for disturbances, leading to more accurate and stable control. That’s why this choice is correct: it describes open-loop as lacking feedback and closed-loop as using sensor feedback to steer toward the setpoint.

The idea being tested is how feedback distinguishes open-loop from closed-loop control in HVAC. In an open-loop system, commands are sent to equipment without checking the actual outcome—there’s no measurement to compare against a target. So you might set a heater or damper to a fixed action, and disturbances like a door opening or more people in the room won’t be automatically corrected.

In a closed-loop system, sensors continuously measure the actual condition (such as room temperature), compare it to the desired setpoint, and adjust the actuators to reduce the difference. This feedback lets the system track the target and compensate for disturbances, leading to more accurate and stable control.

That’s why this choice is correct: it describes open-loop as lacking feedback and closed-loop as using sensor feedback to steer toward the setpoint.