I remember reading this from you before, but that didn't compare to using simple ventilation, and your build may be a little different, as it's a stand alone building.The very first film I watched in my room was before AC was fitted. Admittedly it was August and the internal temp started at 22 degrees.
4 of us were in the room, really excited at the first ever viewing in my purpose built cinema.
We got 45 minutes in before giving up, the temp had risen to 27 degrees and felt like 40! It is in effect the same as Sauna. Loads of body heat and nowhere for it to escape to.
I didn’t watch another film until AC was fitted.