If they're using the same Delta fans the Innosilicon A2 units used, the 3 fans use a total of a bit MORE power than a standard box fan.
On the other hand, LOTS of airflow should help keep the cards cool.
Not sure which ones you speak of.. these are not delta fans.. they are 1.2A@12V three totaling 43.2 watts. Most box fans i know of are almost double that minimum. They really put some air thru this case.
https://i.imgur.com/alDTNaU.jpgtheres the pic of the fans inside this case. I dont think thats bad at all. considering antminer s-9 fans are 2-3 amps. Consisting of two fans. Plus this is much better directed over the cards than a box fan. Win win if you ask me.
BR