Ohhh!!! I'm impressed. The efficiency freak part of me is going crazy.
Looks to be a very elegant solution. Although I don't think you will have to really worry about soaking up heat into the "cool" water side. The difference in temp between the "warm" and "cool" sides will only be about a degree. Maybe even less. Keep in mind how much heat it takes to change the temp of water, so you probably aren't going to be dealing with a very large temperature gradient.