Air changes per hour (ACPH)

Ref. Guideline: ISO 14644

Air changes in pharmaceutical cleanrooms play a significant role in maintaining the clean room quality as per ISO Clean Room Classification through the HVAC system.

Air change per hour is the number of total replacements of any room air in one hour. if the supply of air by the HVAC system in one hours is equal to the volume of the room then it will be one air change per hour. FDA recommends maintaining a minimum of 20 air changes per hour in cleanrooms.

ACPH Calculation steps:

Step 1:

Calculate the air velocity in feet per minute below the HEPA filter.. it is determined at the four corners and the center of the filter and the mean of the five readings is determined.

V= (V1+V2+V3+V4+V5)/5

Where;

V is the velocity observed at each point.

Step 2:

Now calculate the area of the filter by multiplying the length and width of the filter in the feet.

A= LxW

Where;

L- Length of HEPA filter,

W- width of the HEPA Filter

Steps 3:

Calculate the total air volume per minute supplied in the clean room by the following formula:

Q= Any

where;

A= Area of HEPA Filter in square feet

V= Average air velocity in feet per minute

Steps 4:

Calculate the total room volume by multiplying the length, width, and height of the room in feet.

Volume= LxWxH

Steps 5:

Calculate the air change per hour using the following formula:

Air change per hour (ACPH) = Q x 60/volume

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