I have the frozen milk jugs,bottles, tubs etc. I put frozen jugs in a stryo cooler at night, helps cool. I have misters too. Ice in waterers. This morning 4a I removed the soffit vent, left just hardware cloth increased ventilation. I have four windows. The coop is 8x8. I even thought about a/c...its just too hot.
Keep in mind that cool air sinks. So putting frozen bottles in a styrofoam cooler is not going to help cool the air in the coop. It may keep the area around the floor cool, but will do nothing for the hens that are up on the roost. I would put the ice bottles up higher somewhere in the coop (maybe hang them), or behind the fans like I suggested.
