I like to contradanse and have been in similar settings in far hotter climates.  I think that the large fans should be located in the entrance doorways (blowing out) as far away from the gym as possible.  Open the single doors in the gym to get fresh outside air pulled in to cool off the dance floor.  Smaller fans along the gym walls will be quieter and will cool the outside dance lines.  

What you don't want to do is end up fighting the gym's current ventilation system.  You should talk to the building superintendent and ask this same question.

Thanks for the response dvd.  The current Gym has no ventilation.  Will take your advice and see how we get on.  Our dance form is Scottish and have done a bit of contra in my time.  Weather has also cooled off, so that will be a tremendous help.
Bill Z