As the engineer for thermal management device, he will choose the AC fan per ventilation and cooling system requirement. First, engineer will have to verify the power input is AC or DC. Then, the frequency is 50Hz or 60Hz, and main AC power input is 115Vac or 230Vac, and then engineer will choose AC cooling fans based on the size, air flow, statistic pressure and so on. The most popular fan size will be 120x38mm, 80x38mm, 254x89mm, 172x150x55mm, 60x30mm, 92x25mm, 225x80mm, 190x70mm, and if AC fans will be used in a rugged circumstance, the engineer may choose the fans with metal impellers. If AC fans will be used in a high humid environment, then, the engineer can choose AC fans with waterproof. Especially, in those couple years, more and more requirements for green technology, so the engineer may consider the EC fan for the purpose of energy saving.