Paul,
I find your comments rude and uncalled for. My post was kind and meant to help the OP with an answer to his question.
As for the validity of your comments, the thermal capacity of ANY phase change cooling system is finite and predictable. If we know the capacity of the system, we can determine how much water it can cool over a given period of time. It is that simple.
The fact remains the same, a "dorm fridge" does not have the capacity to act as chiller or cool down a 200 gallon tank of water in 120F room.
Lets put this very simply and kindly. If you can show where my math and/or article is wrong, then please do so. I would welcome the learning experience. Yes Paul, HVAC systems are all based on the same concept, nobody said they weren't. The question here is capacity, not the efficiency of the contact between the water and the chiller. You are confusing the two.
As for your 200 gallon system example:
Firstly, antifreeze has LESS thermal capacity (about half as much) than water. It is does not help cooling, it actually reduces cooling capacity of a system (by about half). Why do we use it then? Because it does not freeze.
You mention that you understand the physics. Lets look at your 200 gal example and apply those physics.
The specific heat of water is 1 BTU per degree F per pound. There are 8.33 pounds in a gallon, so it takes 8.33 BTU to heat or cool 1 gallon of water 1 degree F.
The specific heat of 100% Ethylene Glycol (antifreeze) is about .6 BTU per degree F per pound and has a specific gravity of about 1.16 (at the 10F you indicated). So 1 gallon of Antifreeze weighs 9.66 pounds. It therefore takes 5.8 BTUs to heat (or cool) 1 gallon of 100% antifreeze 1 degree F. So you claim you pulled down a 200 gallon system 90F to a steady state temperature of 10F. Lets ignore the fact that the room will continue to try and heat the liquid back up and with a Delta T of 90 degrees, the heat transfer back into the Glycol would be VERY significant. So ignoring the reality that makes your example even harder, a straight 90 pulldown would take 104,400 BTUs. Again, that is ignoring the HEAT in the room that will continually try to heat the liquid back up.
You did not say how long it took to pull the liquid down or what size "chiller" was used. You did not mention insulation or any other aspect of the setup. Nonetheless, I am calling your bluff. If you had a 1 ton chiller (that is 12,000 BTU/hour) with NO external heat input (a perfectly insulated tank!) it would take nearly 9 hours of continuous running to pull the tank down to the 10F. In the real world it would take a 2 ton unit three times that long in a 100F room. Why? Because of the losses involved in the system and the ambient temperature that we are fighting against. Glycol cooling systems are used in buildings with resevoirs MUCH smaller than 100 gallons and they require compressors much larger than 2 Tons. How do I know this? I work with them.
Anyway, we can apply the same physics to your 120F room. If the target fish tank temperature was 75 degrees, then you are looking at a 45 degree pulldown from ambient. Again, we will ignore the heat being added back into the system, as it only makes matter worse. Lets take a 100 gallon tank as an example. To achieve a 45 degree pulldown we would need to remove 37,485 BTUs from that tank. It would take the dorm fridge over 75 hours of continuous operation to pull the tank down to the target temperature. In reality the 500 BTU/hour dorm fridge would never be able to keep up with the 120F heat load in the room and the tanks steady state temperature would only be a few degress less than 120F. Again, basic physics and the finite capacity of the dorm fridge.
As you can see it is all about the capacity of the system, not the efficiency of the heat transfer. Even at 100% efficiency, if the compressor is too small, then the system will not reach the target temperature. Getting upset at me is not going to change the physics.
I am sorry to call your bluff this way, but your assertions are simply not even remotely possible and you have responded in a rather condescending and rude manner with information that is simply not supported by any stretch of the facts or phsyics.
Now if you come back and tell us that you used a 2 Ton capacity compressor, then I will be more than happy to believe you.