The widespread adoption of CO2 refrigeration compressors was held back for decades due to one major engineering hurdle: the extremely high pressures at which the refrigerant operates. A conventional refrigeration compressor operates at pressures of around 15-20 bar (217-290 psi). A transcritical CO2 compressor, on the other hand, must be able to handle pressures of up to 120 bar (1,740 psi). This ten-fold increase in pressure requires a completely different approach to compressor design and manufacturing.

The high-pressure challenge affects every single component of the compressor. The compressor casing, for example, must be much stronger and more robust to contain the immense internal pressure. The pistons, connecting rods, and crankshafts must be able to withstand much higher loads. The lubrication system is also critical; it must be able to function effectively at high pressures and temperatures to prevent premature wear and tear. The seals and gaskets are another key area of concern; they must be specially designed to prevent leaks of high-pressure CO2, which is much more difficult to contain than conventional refrigerants. The manufacturing process for these components must also be incredibly precise to ensure the highest level of quality and durability.

The high-pressure operation also affects the compressor's efficiency. The energy required to compress a gas to such high pressures is significant. However, engineers have found clever ways to mitigate this. For example, some CO2 compressors use variable speed drives (VSDs). A VSD allows the compressor to operate at different speeds, which enables the system to match its cooling capacity to the exact load. This is much more efficient than a traditional on/off compressor, as it avoids the energy-intensive process of starting and stopping the motor. By varying the speed, the system can operate at a lower pressure ratio, which improves its overall efficiency, especially in mild climates.

Another innovative solution is the use of parallel compression and ejectors. Parallel compression uses a secondary compressor to handle a portion of the gas, which reduces the load on the main compressor and makes the entire system more efficient. Ejectors use the pressure drop of the high-pressure gas to create a venturi effect that pulls in and compresses the low-pressure gas, which significantly improves the system's COP. These engineering solutions are a testament to the fact that the high-pressure challenge is not an insurmountable obstacle but an opportunity for innovation. The development of robust, efficient, and reliable CO2 compressors has been a long and challenging journey, but the result is a technology that is poised to lead the refrigeration industry into a more sustainable and energy-efficient future.