Originally Posted by ExpertBrewers
The water would most likely heat up really quickly. Any heat you take out of the wort is going straight into that water.
Damn...works out to about 45 pounds of ice. Going by the differences in heat of fusion (333J/g) and heat capacity of water (4.18J/g*degreeC) I didn't think that would have been an issue. Those pesky laws of thermodynamics are a pain.
We used a somewhat similar design to cool keg beer at one of my jobs. 8 pounds of ice was generally enough for at least 1 keg. Guess the temperature change wasn't nearly as large in that case though.