CO₂ Chats - What is meant by transcritical and subcritical operation when it comes to CO₂ systems?

What is meant by transcritical and subcritical operation when it comes to CO₂ systems? Copeland's Andre Patenaude, director – solutions strategy, answers this question and describes when a system is above the critical point (87.8 degrees Fahrenheit), it’s in transcritical mode – when below the critical point, it’s in subcritical mode.