I did not realize how profoundly the AC was affecting my dog until we got some kennels installed in the garage. Our garage is under the house and throughout the summer stays at least 10* cooler than the outside and with the big fans on, the dogs are just fine. They stay down there during the day except for training, airing, etc and then spend the night in the house with us.
2 years ago I could not even do light work this time of year without my dog getting dangerously hot, (ragged breathing, long recuperation, tongue dragging on the ground, etc.) He just could not take the transition from being in the ac all the time to our heat and humidity combination. Now that we have the kennels he is doing just fine. Of course I am still super careful, we quit by 9:00 AM but he has a far easier time of it.
Not to mention, as was suggested to me by Kristie, it really helps them to focus better when they don't have run of the house or yard all day.