A BLDC fan takes in AC voltage and internally converts it into DC using SMPS. BLDC uses a combination of Permanent Magnets and Electronics to achieve the kind of efficiency and performance it delivers.
In a BLDC motor, as there are no brushes so the commutation is done by the driving algorithm in the Electronics. Hence no wear and tear of brushes making the motor more rugged for long-term use.
One added advantage in a BLDC fans due to use of an electronic circuit is that you can add several additional features to increase convenience, few example of the same are sleep mode, timer mode also it is compatible with Home automation systems.
Compared to regular induction fan, a BLDC fan can save enormously upto Rs 1000-1500/ Year/fan. And because there is no heating of the motor, the life of a BLDC fan is also expected to be much higher than ordinary fans.