JPSmithcm1 -
"Neat stuff.

I've been kind of struggling to wrap my head entirely around trans-critical CO2 refrigeration.

It's a weird system."

Maybe this will help JP - These three articles are from ACHR News back in 2003 - 2004 on Transcritical and Subcritical refrigeration that explains it pretty well.

The first one explains the cycle and the last two are examples of installations in a supermarket in Copenhagen, Denmark in the first one(pretty interesting), and system compatibility and safety in the second one.