It is very similar to a HERMS system. In the end, I did a sort of dry run, hooking up everything in the right order. It became apparent that I didn't need the second coil at all (that I could simply draw the sparge water off from the ball valve, and run the return into the top of the sparge tank (an open rather than closed system, eliminating pressure concerns- running a closed coil system was a Very Bad Idea!).
I am still on the fence regarding whether to run hot sparge water through the coil in the mash tun, or run the wort through the coil in the sparge tank. The heat transfer physics of it seem similar, except for a couple of minor issues. First, I'd rather not run hot wort inside my copper coil. While the wort is hot, theres no issue, but when it starts to cool down after the mash, the lefteover wort starts to stick in the coils, causing sanitation concerns (basically resulting in more clean up effort). Second, I have a bit of concern that circulating the wort might add hot side aeration to it (though I have heard that this is less of a major concern than previously thought). Third, I don't want to denature the enzymes in the wort by exposing them to high heat (~170* in the sparge tank). It seems like I'd be better able to buffer the temperature difference by running a small amount of hot (~170*) sparge water through a large amount (8G) of wort (while stirring), as opposed to running a small amount of 150* wort through a lot of very hot sparge water.
Are any of these concerns valid, or am I missing something? Anyone have ideas/opinions? I'd appreciate the feedback. Thanks-