DYI chiller

Brad:  I don't know, it's been like 9-10 yrs since I last looked into it.  There are a few assumptions for heat transfer correlations I had to make.  I'm sure I don't have the calcs laying around anymore, but I might look into it again.  I just seem to recall that at first pass, it didn't seem too promising.

The average reef chiller is 1/5 to 1/2 horsepower and designed for maximum heat transfer (titanium shell and tube exchanger).  The average dorm fridge is 1/20 hp and is designed to keep beer cold... my gut feeling is that placing a UV sterilizer in the fridge is not going to make much of a difference (but I ain't calling anyone a liar  and I'd love to see someone local give it a try so I could see firsthand).  Just scaling down the horsepower for the dorm fridge makes it suitable for a 20 gallon aquarium (assuming the 1/5 hp is for a 75 gallon tank).

Maybe the guy at reefs.org just forgot to mention the fan he installed in his hood or sump or the fact that he had central air installed in his house .

Sadly, Jon is correct. Ten years ago or so there was a lot of effort from various groups to invent the DIY chiller.

The bottom line is that the calculations are pretty straightforward.

If a chiller drops 100 gallons 10 degrees, then it can only drop 200 gallons half as much, or 5 degrees - same amount of heat energy removed from the water.

Applying the same principle to the ice-bottle scenario, if you freeze 2 liters of water (about 1/2 gallon) that will bring the ice to 32 degrees - adding that block of ice to 100 gallon tank, at 80 degrees will result in one half gallon of frozen water increasing about 50 degrees to the tank temperature, which will reduce the 100 gallons temperature 1/200 as much (since its 200 times more water), only 1/4 of a degree.
So, to decrease the 100 gallon tank 10 degrees, you need to increase the temperature of 20 gallons of ice by 50 degrees. (of course there is a lot of rounding off here, but you get the idea). That is why ice bottles only work for small tanks or small temperature changes.

A chiller for a 200 gallon reef is going to be like 1/2 horsepower, many times the power of any dorm fridge. The dorm fridge simply won't work - the laws of conservation of energy. There is something more going on for the guy who says he dropped his 200 gallon reef 10 degrees. Perhaps he also added a fan or something.

Evaporation can take out a lot of heat, because as water changes form from liquid, it removes a significant amount of heat energy in making the state change. Fans work really well for this reason, and can drop a tank temperature a good way below the air temperature if you have enough evaporation going on. This is of course the principle of the swamp cooler.

You could get a compressor from a large freezer or a commercial unit, and rework with plumbing to be a viable chiller - but I suspect it will be just as cheap to buy an aquarium chiller designed for efficient transfer to water, and corrosion proof.

Has anyone given serious thoght to using the underground heat exchanger idea? I have been thinking about it for a while, but I haven't found any info on average temps for soil in this area (West Valley). Or even how deep to go to get stable temps. Anyone have some sites that might help?

Simply put. Chillers are a luxury and in some cases necessary. Time is money.... Once you spent the time and the money to build something that may or may not work, you could just spend the money and be done with it and not waste all the time and effort doing so. Some things are worth the effort doing yourself for sure. But in this case I would shell out the money and be done with it. I do have to agree with Mike. Putting the sump in the basement would do wonders. Sounds like that is not an option for Marcus.
I would love to have a 77deg tank. But to me it wasn't worth the luxury to drop my tank 3 deg from 80 for $500-$1000. The corals will just have to adapt if they want to live in my tank. :-)