Another thing you can do is to wrap a few bottles of frozen water in a towel/fleece and place it in the cage and place other frozen bottles around the cage. You can also take small dishes (like finger bowl) and place ice cubes in them and set them inside the cage. The piggies can lick the ice and as long as you change it frequently it is not a problem. As a last resort you can also make a poor man AC for them also. How you do this is that you get a block or large bag of ice, then place it in front of a fan (make sure the fan isnt blowing directly on the piggies though) and turn the fan on. If you put your hand in front of it you'll feel the cool air blowing. Downside is that the ice melts pretty quick and makes a nice puddle.