A friend of mine years ago had this problem for an upstair room and she and her husband decided to have a room a/c permanently installed in the wall. It didn't look bad, could be turned off when she was out of that room, and cooled up quickly when she wanted to work in the room. Said it didn't seem to add a lot to the electric bill. Oh, her problem was that the room wasn't hooked up to the central air and the ac unit wasn't large enough to add duct work to that room.