CO2 supermarket refrigeration operation

[kooltek]

Have been reading alot on CO2 pack systems. Just starting to make appearnces in U.S. thanks to Hill-Phoenix. I see many supermarket chains in UK and germany and other countries using CO2 now, even in the trans-critical area, I have a question:
In a system designed for trans-critical operation, when the ambient temp. drops to 5deg to 10 deg C does the discharge gas actually condense in the gas cooler and operate as a sub critical system? And how does the high pressure expansion valve react under these conditions? I figured someone in this forum may know about these systems. Thanks

[NoNickName]

Yes, most of the time, a transcritical system actually is a subcritical one. The expansion valve is capable of adapting to both cycles, because the management control detects the condition.
And because the isotherms around the critical point are so horizontal, and therefore the enthalpy is low, the system is adjusted to "jump" and avoid that area.