AC drives can be used for HVAC systems that require ___.

• A. Harmonic correction
• B. Speed control
• C. Single-phase motors
• D. Efficiency improvement

Answer: (B)

AC drives (variable frequency drives) change the speed of an AC motor by adjusting the frequency and voltage supplied. In HVAC, the big need is to vary airflow and water/pump flow to match the cooling or heating load, maintain proper duct pressures, and respond to changes in demand. By giving you precise speed control, you can throttle fans and pumps rather than running them at full speed all the time, which saves energy and reduces noise. The power needed by fans and pumps grows rapidly with speed (roughly with speed cubed), so even small adjustments in speed lead to meaningful energy savings and better comfort. While other features like smooth ramping or harmonic management can be useful, the primary reason HVAC systems use AC drives is to achieve effective speed control.