Solar panels on the roof of this structure will heat glycol which in turn heats the water to run through tubing laid in the concrete slab.  Looks simple, but… we all got tangled up in this stuff before figuring out how to lay it neatly in loops of equal length (so the hot water monitoring system would not get confused!).  Prior to laying the tubing, we bought recycled foam insulation panels from a company which salvages good insulation from demolition sites.  This makes a cocoon to preserve heating in the building — necessary because this is a “NetZero” building — no furnace, no heat other than this system.  Great insulation everywhere was a necessity.