Of the following, centrifugal refrigerant machine is best characterized by:

• A. High pressure high temperature machine
• B. Low volume high pressure machine
• C. High volume low pressure machine
• D. High pressure high volume machine

Answer: (C)

Centrifugal refrigerant machines are designed to move large amounts of refrigerant with a relatively modest pressure rise, so they are best described as high-volume, low-pressure devices. The centrifugal compressor uses a rapidly spinning impeller to impart velocity to the refrigerant and then converts that velocity into pressure. This setup yields very high flow (capacity) suitable for large chillers, but the pressure increase (head) per pass is not as extreme as with other compressor types. That combination—very high volumetric flow with lower discharge pressure—is why the correct characterization is high volume, low pressure. The other descriptions imply either a much higher pressure rise or a much smaller flow, which doesn’t match how centrifugal compressors are used in large-scale refrigeration and HVAC systems.