[elhigh]

I was going to say what Snax said - earth tubes, while effective, get gross before long.

I've had this idea but haven't followed up on it - burying a couple hundred feet of plastic pipe and pumping water through the pipe would cool the water off, then run the water through a water-air heat exchanger somewhere in your house or in your HVAC loop. It doesn't even have to be connected to your AC system, it could just be one of those things that's there to temper the air temperature. It could, conceivably, do a fair amount of cooling without having to resort to your conventional AC at all.

Now, before anybody flames me on lousy heat conductivity of plastic pipe - I know! And yet, it works well enough. And do you really want to take out a second mortgage for a similar length of copper? For what you pay for copper, you can lay out enough plastic pipe to cool yourself, and a neighbor on either side.