Air is only 0.04% CO2 but 78% nitrogen. Instead of dry ice we need to standardize solid nitrogen as a portable, single-use coolant.

Instead of cooling the whole room it’s more efficient to cool individual people though. Which means taking advantage of their sweat’s evaporation would make more sense. So like those reflective Japanese jumpsuits with fans at the bottom and outlets at the top are probably the best design. A little sublimating gas in the suit couldn’t hurt though (depebding on where the container is).