4)i dont follow your question. there is no pressure tank in this system.
is there a way to design this system so that it wouldn't freeze in the winter? I don't like the idea of a pipe filled with coolant going through my water.
You can't put antifreeze in the water tank. It would be a consumed item, so it would be expensive. You don;t want to be drinking it, cooking with it or washing with it.
OK, gotcha. That wasn't evident from the first diagram. A closed loop system makes the use of antifreeze an option.
I'm talking about running a closed loop collector system with a coil in the tank with would transfer the heat to the water. I think a system like the one below would be just fine. I just dont want to use coolant (or any toxins for that matter) anywhere even near my water supply. I'm one of those wierdos who won't even drink fluoridated tap water