I agree with skae. My room gets particularly hot during the summer, and i have on of those window A/C machines that works fantastically. Get's my room to a nice cold temperature when it's really hot outside, and it used to drop my tank temp down a degree or two as well.
However, you need to watch out because you can't have the temperature drop drastically otherwise you could stress out your livestock. It needs to be a slow drop in temperature in order for your animals to stay comfortable.