What is the correct compression ratio if the suction pressure is 33 PSIG and the discharge pressure is 181 PSIG?

To determine the correct compression ratio, you use the formula that divides the absolute discharge pressure by the absolute suction pressure. The calculations require converting the gauge pressures into absolute pressures by adding atmospheric pressure, which is typically around 14.7 PSIA.

First, convert the suction and discharge pressures from PSIG to PSIA:

• Suction pressure: 33 PSIG + 14.7 PSIA = 47.7 PSIA

• Discharge pressure: 181 PSIG + 14.7 PSIA = 195.7 PSIA

Next, calculate the compression ratio:

Compression Ratio = Discharge Pressure (absolute) / Suction Pressure (absolute)

Compression Ratio = 195.7 PSIA / 47.7 PSIA ≈ 4.10 : 1

This calculation confirms that the correct compression ratio, based on the given suction and discharge pressures, is approximately 4.10 : 1. Therefore, this ratio accurately reflects the relationship between the pressures in the system, making it essential for understanding efficiency and performance in HVAC and refrigeration systems.