EC (electronically commutated) fans are considered to be the most energy efficient fans on the market. These fans allow for the efficiency of a DC fan without the hassle of needing a AC to DC power supply.
EC fans have a flexible peak operating range unlike traditional AC fans, which have a very specific range (often disrupted by minor fluctuations in voltage). This means that if speed is slightly increased or decreased, output and energy usage will remain relatively linear. A similar AC fan in that environment would either drastically drop airflow output or drastically increase energy usage. They also allow for brushless communication if you need to reverse polarity (make the fan spin the other way). This previously was only available with brushed motors which add significant noise and significantly drop motor lifespan.