The compression ratio in a system can be determined by:

The compression ratio in a system can be determined by:

• A. Multiplying discharge gage pressure by suction gage pressure.
• B. Dividing discharge pressure absolute by suction pressure absolute.
• C. Dividing suction pressure absolute by discharge pressure absolute.
• D. Subtract suction pressure absolute from discharge pressure absolute and divide by 12,000 btu/hr.

Answer: (B)

Compression ratio is the measure of how much the gas is squeezed, defined as the discharge pressure divided by the suction pressure, using absolute pressures. Using absolute pressures matters because atmospheric pressure is present in both readings; gauges remove that baseline, so gauge values wouldn’t give a true, comparable ratio. By taking the discharge absolute pressure and dividing it by the suction absolute pressure, you get a true, dimensionless ratio of how much the gas is compressed. The other approaches mix gauge pressures, mix different units, or use subtraction and a heat-rate term, none of which correctly define the compression ratio.

Compression ratio is the measure of how much the gas is squeezed, defined as the discharge pressure divided by the suction pressure, using absolute pressures. Using absolute pressures matters because atmospheric pressure is present in both readings; gauges remove that baseline, so gauge values wouldn’t give a true, comparable ratio. By taking the discharge absolute pressure and dividing it by the suction absolute pressure, you get a true, dimensionless ratio of how much the gas is compressed. The other approaches mix gauge pressures, mix different units, or use subtraction and a heat-rate term, none of which correctly define the compression ratio.