For those who don't have something like these, please remember to put in frozen water filled 2 liter bottles for your rabbits. Don't let them suffer from heatstroke. Take care watching for rapid breathing/panting and moistness around the nostrils. You can also wet their ears with cool water. Do not get water inside their ears. Set up fans, keep direct sunlight off them. I've heard of freezing ceramic tiles for them to lay on. You can wet and freeze a towel for them to lay on. Just be sure to remove it when the coolness is gone, otherwise it will not help cool them and will reduce airflow around them. Keep water dishes and bottles filled with CLEAN FRESH water at all times.
Run fans without directly blowing it on the rabbits. On very hot days we have four fans running though it is cooler inside with the concrete floor than outdoors. One fan in front pulls in air, the fan in back blows it out. A fan in the first aisle pointing towards the back and a fan in the last aisle pointing towards the front also help to bring cooler air around the cages and creates air exchanges at the same time.
Rabbits can take cold easier than they can take the hot. They do not sweat but release heat thru their ears. If you see a rabbit in heat distress, bring it inside your house. Put them on a cool floor, perhaps in a bathroom with the door shut if you have no indoor cage. Do whatever it takes to get and keep them cool.
Whenever you can make your rabbits lives more comfortable, please do so. Don't handle, hold or pet them on hot days. Save the grooming for cooler evenings.