My DD was around 6 months old during the hottest part of last summer and we did not have air conditioning. One thing I did to keep her cool and also amused was to fill her highchair tray with water and let her splash about- she was sitting strapped in so was safe and I would add toys to her tray and place her chair on the tiles. I'd have her in just a nappy and she would happily drench herself and I'd just keep topping up the water for her.
Also I would give her a wet flannel/face washer to hold when I put her to bed, which she enjoyed sucking on until she fell asleep- some nights it was the ONLY thing that would calm her down and get her to sleep if she was crabby from the heat.
I also found a nice shady spot in the backyard and took her out in her baby bath (used it like a little pool) with lots of toys etc.
Having no air con sucks- thankfully we finally have one for this summer.