How Do We Calculate Required Airflow in a Cleanroom?

In cleanroom engineering, airflow calculation is not a single-step process. It's a combination of multiple components that ensure cleanliness, pressurization, and system reliability.

Total Airflow = ACH Airflow + Fresh Air + Leakage +Heat Load Air (converted)

So how do engineers determine the right airflow?

Step 1. Air Changes per Hour (ACH) Method

This is the most widely used approach.

Airflow = ACH × Room Volume

Depending on the cleanroom classification:

ISO 5 ⏩240-600 ACH

ISO 6 ⏩ 90-180 ACH

ISO 7 ⏩ 30-60 ACH

ISO 8 ⏩ 10-25 ACH

This ensures that the air inside the room is replaced multiple times every hour to maintain cleanliness.

Step 2: Calculate Room Volume

Room size: 10m x 5m x 3m

Volume 150 m³

Step 3: Calculate ACH Airflow

Formula:

Airflow = Volume × ACH

ACH Airflow = 150 x 25 = 3750 CMH

Step 4: Add Fresh Air

Typically 10-20% or as per standard

Assume: 750 CMH

Step 5: Safety Margin (5%)

5% of 3750 = 187.5 CMH

Step 6: Add Leakage Airflow

Air lost through doors, gaps, and openings
Important for maintaining positive pressure

10% of 3750 = 375 CMH

Step 7: Heat Load → Convert to Airflow

QHeat = 1.2 × △ Theat Load × 3600

Assume:

Heat Load = 5 kW (5000 W)

△T = 10°C

=1500 CMΗ

Step 8: Total Airflow

Total Airflow = ACH Airflow + Fresh Air + Leakage + Heat Load Air

Total Airflow =3750+750+187.5+375+1500=6562.5 CMH

Simple Understanding

ACH Airflow →Cleaning
Fresh Air→ People & oxygen
Leakage → Pressure control
Heat Load → Temperature control

Cleanroom airflow is not just calculation... it's about maintaining cleanliness all the time.

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