Calculation of Air Changes and Air Velocity: Formula, Example, and Cleanroom Acceptance Criteria

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Introduction

In cleanroom, pharmaceutical, and biotechnology industries, airflow control plays a vital role in maintaining cleanliness, preventing contamination, and ensuring product quality...

What is Air Change?

Air Change per Hour (ACH) represents how many times the entire volume of air inside a room is replaced by fresh filtered air in one hour...

Formula for Air Changes per Hour (ACH)

ACH = (Q × 3600) / V

Example Calculation

Room Size: 5 m × 4 m × 3 m
Air Flow Rate: 0.8 m³/s
ACH = (0.8 × 3600) / 60 = 48 Air Changes/hour

What is Air Velocity?

Air Velocity is the speed at which air moves through a HEPA filter or diffuser outlet...

Formula for Air Velocity (V)

V = Q / A

Example Calculation

Q = 0.45 m³/s
A = 0.36 m²
V = 0.45 / 0.36 = 1.25 m/s

Recommended Air Change & Air Velocity Standards

Cleanroom GradeAir Changes/hour (ACH)Air Velocity (m/s)Remarks
Grade A90–1000.36–0.54Laminar Airflow
Grade B40–600.30–0.45Background to Grade A
Grade C20–400.25–0.35General Clean Area
Grade D10–200.20–0.30Support Area / Corridor

Importance of Air Changes and Air Velocity

  • Ensures Contamination Control
  • Maintains Pressure Cascade
  • Ensures Proper Air Mixing
  • Ensures Regulatory Compliance
  • Optimizes Energy Efficiency

Verification and Acceptance Criteria

During qualification, air velocity and air change rates are measured and verified...

Conclusion

Accurate calculation of Air Changes and Air Velocity is vital for maintaining cleanroom classification and ensuring sterile processing conditions...

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