A Variable Frequency Drive (VFD) is an electronic controller that adjusts the speed of an electric motor by varying the frequency and voltage of the power supplied to it. In HVAC, VFDs are used to control the speed of compressors, fans, and pumps, enabling precise capacity modulation rather than simple on/off operation.
VFD-controlled systems (also called inverter-driven) can reduce motor speed to as little as 10-20% of maximum, dramatically reducing energy consumption. Fan and pump energy consumption decreases with the cube of speed — reducing speed by 50% reduces energy consumption by 87.5% (0.5³ = 0.125). This law makes VFDs among the highest-ROI energy efficiency measures in HVAC.
Mini-split systems pioneered inverter-driven compressor technology in residential applications. Modern high-efficiency central HVAC systems increasingly incorporate VFD-driven compressors and fan motors for superior efficiency and comfort.