What is the compression ratio for a screw compressor?

What is the compression ratio for a screw compressor?

• A. 20:1
• B. 4:1
• C. 8:1
• D. 12:1

Answer: (A)

The compression ratio is the discharge pressure divided by the suction pressure, using absolute pressures. For a screw compressor in an ammonia refrigeration system, a single-stage unit is designed to raise the vapor from the evaporating (suction) pressure up to the condenser (discharge) pressure, which typically results in a relatively high ratio. In many ammonia installations this ratio is about twenty to one, meaning the discharge absolute pressure is roughly twenty times the suction absolute pressure. For example, if suction is near 14.7 psia (0 psig) and discharge is about 294 psia (20 bar absolute), the ratio is close to 20:1. The other options represent much smaller pressure rises and are not characteristic of a typical single-stage screw compressor in ammonia service.

The compression ratio is the discharge pressure divided by the suction pressure, using absolute pressures. For a screw compressor in an ammonia refrigeration system, a single-stage unit is designed to raise the vapor from the evaporating (suction) pressure up to the condenser (discharge) pressure, which typically results in a relatively high ratio. In many ammonia installations this ratio is about twenty to one, meaning the discharge absolute pressure is roughly twenty times the suction absolute pressure. For example, if suction is near 14.7 psia (0 psig) and discharge is about 294 psia (20 bar absolute), the ratio is close to 20:1.

The other options represent much smaller pressure rises and are not characteristic of a typical single-stage screw compressor in ammonia service.