Alternating current (AC) is electrical current that periodically reverses direction, flowing forward and backward in a circuit. In the United States, AC frequency is standardized at 60 Hz, meaning the current reverses 60 complete cycles per second. This standard applies to all residential and commercial HVAC equipment in North America.
Technical Details
AC current is mathematically described as I(t) = I_peak × sin(2πft). The RMS value, used in electrical calculations, equals I_peak / 1.414. Typical residential circuit breakers carry 15 to 20 amperes AC, while commercial HVAC compressors may draw 50 to 200 amperes AC. AC waveforms have positive and negative half-cycles lasting 8.33 milliseconds each at 60 Hz.
Applications in HVAC
AC motors are standard in all HVAC applications because the oscillating magnetic field naturally produces rotational torque without additional commutation mechanisms. AC induction motors achieve 88 to 95 percent efficiency and require minimal maintenance compared to DC motors. Three-phase AC motors in commercial systems deliver 25 to 35 percent more horsepower per unit size than single-phase AC motors of equivalent weight, making them preferred for large chillers and compressors.