It was brutally hot here last summer and I nearly lost a couple of hens to the heat even with a mister going, so I got creative. I built a couple of small structures out of cinderblocks my dad had lying around, put a roof over them, and then ran the mister on one or the other (I switched it every day or so to avoid the risk of disease from the soggy ground.) The water soaked into the blocks, and as the breeze blew, the water evaporated, cooling the inside of the structure. Once I showed my chickens how to use the structures, they had no more problems. They'd go in when they got too hot, and come back out when they'd had a chance to cool off.

A few of our hens chillin' inside of the "cool box" I built. I also constructed breezeways for hens who preferred to be in a less confining space. As an added bonus, the chickens would stand in the trays of water where the water dripped from the roof, and loved to drink from the overflow. The hardest part about this whole project was getting the hose on just the right setting that it barely misted the bricks without over-saturating them, but not so lightly that it didn't cool off enough.
A few of our hens chillin' inside of the "cool box" I built. I also constructed breezeways for hens who preferred to be in a less confining space. As an added bonus, the chickens would stand in the trays of water where the water dripped from the roof, and loved to drink from the overflow. The hardest part about this whole project was getting the hose on just the right setting that it barely misted the bricks without over-saturating them, but not so lightly that it didn't cool off enough.