At work we have one of those standalone/portable air conditioning units. They come with a tube that you vent with, and requires substantially less window space than the types that sit mostly outside of the window. The disadvantages, however, are that they are very loud as they are inside your room, and they also need to be drained because they collect the water instead of letting it drip to the ground.
Even one of those ones would require some modification to fit in the casement windows that you have, however.
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