I drew up a schematic for a single tier with three way valves circulating through an immersion chiller for HERMS. If you can't see the pic below (I can't), here's the link to a bigger one (use the magnifying glass and + to zoom in):
The plan was originally for an electric HLT and BK, but would also work with a gas HLT and BK.
If that doesn't work, PM. I have a better resolution PDF.
Ignore the "drain" stage.