What is a key operating characteristic of CO2 (R-744) systems and a primary design precaution?

What is a key operating characteristic of CO2 (R-744) systems and a primary design precaution?

• A. They operate at very high pressures; components and fittings must be pressure-rated and robust to avoid leaks and ruptures.
• B. They operate at low pressures; standard components suffice.
• C. They require no special high-pressure components; typical refrigerant lines are fine.
• D. They operate at medium pressures similar to R-134a.

Answer: (A)

CO2 systems operate at much higher pressures than many other refrigerants. CO2 has a relatively high critical pressure (around 73 bar, or about 1,070 psi), and in practice the high-side pressure in many CO2 designs—especially transcritical cycles—can reach tens of bar to well over 70 bar depending on load and conditions. Because of these elevated pressures, every part of the system must be designed to withstand them: the compressor, valves, piping, fittings, and vessels need to be pressure-rated and built with robust joints and seals to prevent leaks or ruptures. Using standard low-pressure components would risk leaks, failures, or safety hazards under CO2 pressures. This high-pressure demand is a defining design precaution for R-744 systems.

CO2 systems operate at much higher pressures than many other refrigerants. CO2 has a relatively high critical pressure (around 73 bar, or about 1,070 psi), and in practice the high-side pressure in many CO2 designs—especially transcritical cycles—can reach tens of bar to well over 70 bar depending on load and conditions. Because of these elevated pressures, every part of the system must be designed to withstand them: the compressor, valves, piping, fittings, and vessels need to be pressure-rated and built with robust joints and seals to prevent leaks or ruptures. Using standard low-pressure components would risk leaks, failures, or safety hazards under CO2 pressures. This high-pressure demand is a defining design precaution for R-744 systems.