No this isn't a new idea at all, but I thought that I'd share this with all of you. I found this little fridge and what I think sets it apart is the fact that it also runs off of battery power. Meaning that if you had a battery powered pump, then you could effectively also keep your tank cool if there was no electricity for a while. I'm sure that the electrical geniuses will be able to shed some more light on anything I'm missing.
Other Travel - Desk Fridge for sale in Cape Town (ID:46941533)
Essentially the idea is to have the following:
-Bar fridge
-long plastic pipe
-pump
-thermostat (if you're not at home to keep an eye on things)
You would place the pump with thermostat switch, in your sump, attached to one end of the pipe. You would drill an entrance hole in the side of the fridge for the pipe to go into and create many coils in the fridge with the pipe and drill another hole for the pipe to exit back out, into your sump. Simple as that. Hope you like the idea.