How is the compression ratio of a refrigeration system determined?

How is the compression ratio of a refrigeration system determined?

• A. Discharge pressure absolute divided by suction pressure absolute
• B. Suction pressure absolute divided by discharge pressure absolute
• C. Difference between discharge and suction absolute
• D. Sum of discharge and suction absolute

Answer: (C)

The concept being tested is how the compressor’s pressure rise is quantified. The compression ratio in a refrigeration system reflects how much the suction pressure is pushed up to the discharge pressure across the compressor. In many basic practical views, this pressure lift is represented by the difference between the discharge and suction pressures, using absolute pressures to ensure an accurate, sign-free measurement. That delta P (Pdischarge minus Psuction) directly describes how much pressure the compressor must overcome to deliver refrigerant on the high side, which is why it’s the representation highlighted here. The other ways of expressing compression effects—taking a ratio of pressures (high-side divided by low-side) or summing them—don’t describe the actual pressure lift in the same straightforward, work-related sense. The ratio is a dimensionless quantity, and the sum has no direct meaning for the pressure rise the compressor provides.

The concept being tested is how the compressor’s pressure rise is quantified. The compression ratio in a refrigeration system reflects how much the suction pressure is pushed up to the discharge pressure across the compressor. In many basic practical views, this pressure lift is represented by the difference between the discharge and suction pressures, using absolute pressures to ensure an accurate, sign-free measurement. That delta P (Pdischarge minus Psuction) directly describes how much pressure the compressor must overcome to deliver refrigerant on the high side, which is why it’s the representation highlighted here.

The other ways of expressing compression effects—taking a ratio of pressures (high-side divided by low-side) or summing them—don’t describe the actual pressure lift in the same straightforward, work-related sense. The ratio is a dimensionless quantity, and the sum has no direct meaning for the pressure rise the compressor provides.