Cleanroom Air Changes Per Hour (ACH): 

How does high ACH contribute to contamination control in cleanrooms?

Answer: High ACH contributes to contamination control in the following ways:

• Rapid Dilution: It quickly dilutes airborne contaminants to harmless levels, which are then exhausted or filtered out by high-efficiency filters (like HEPA or ULPA).
• Particle Removal: Continuous airflow sweeps suspended particles towards exhaust vents or return air grilles, reducing their residence time in critical areas.
• Maintenance of Unidirectional/Laminar Flow: In higher-grade cleanrooms, high ACH helps establish and maintain unidirectional (laminar) airflow, ensuring air moves at a uniform velocity and direction across critical zones, effectively "washing" contaminants away from the work area.
• Prevention of Cross-Contamination: Combined with proper pressure cascade design, high ACH ensures air always flows from cleaner to less clean areas, preventing external contamination from entering.

What factors influence the required ACH in a cleanroom?

Answer: Several factors determine the required ACH for a cleanroom, including:

• Required Cleanroom Classification: Higher cleanliness classes demand higher ACH rates.
• Internal Contamination Sources: More particulates and contaminants generated by equipment, personnel, or processes within the cleanroom will necessitate higher ACH.
• Personnel Density: Human activity generates particles, so areas with more people require higher ACH.
• Heat Load from Equipment: Heat dissipated by equipment needs to be carried away by increased air circulation.
• Process Type: Processes involving chemicals or biological agents, for instance, might require higher air exchange rates.
• Room Layout and Size: The physical dimensions and airflow pattern design of the room influence the effectiveness of ACH.

What are typical ACH rates for different cleanroom classifications?

Answer: ACH rates for cleanrooms vary significantly based on their required cleanliness classification (e.g., ISO 14644-1 standard). Here are some typical ACH ranges for common cleanroom classes (note: these are guidelines and can vary based on application and design):

• ISO 8 (Class 100,000): 5 - 48 ACH
• ISO 7 (Class 10,000): 30 - 90 ACH
• ISO 6 (Class 1,000): 90 - 180 ACH
• ISO 5 (Class 100): 240 - 600 ACH (or higher, depending on airflow patterns)

WHow do you calculate ACH for a room?

Answer: The formula for calculating ACH is:

ACH = (Supply Airflow CFM * 60) / Room Volume (Cubic Feet)

Or

ACH = (Supply Airflow CMH) / Room Volume (Cubic Meters)

Where:

• Supply Airflow CFM (Cubic Feet Per Minute) is the volume of air supplied into the room per minute.
• Supply Airflow CMH (Cubic Meters Per Hour) is the volume of air supplied into the room per hour.
• Room Volume is calculated by multiplying the room's length, width, and height.

Why is ACH so important in a cleanroom?

Answer: ACH is critically important in cleanrooms because it directly impacts air cleanliness. High ACH helps to:

• Dilute and remove contaminants: Rapidly clear airborne particulates, microorganisms, and chemical gases generated within the room.
• Maintain positive pressure: Ensure the air pressure inside the cleanroom is higher than the surrounding areas, preventing unfiltered air from infiltrating.
• Control temperature and humidity: Maintain stable environmental conditions, which are crucial for sensitive manufacturing processes and preventing microbial growth.
• Meet cleanroom classification standards: Achieve the required air cleanliness levels mandated by specific ISO or other cleanroom class standards.

What is Air Changes Per Hour (ACH)?

Answer: Air Changes Per Hour (ACH), also known as the air exchange rate, is a measure of how many times the entire volume of air in a defined space is replaced with new (conditioned and filtered) air within one hour. It quantifies the efficiency of a ventilation system in exchanging indoor air. For example, if a room has an ACH of 10, it means the air in that room is completely replaced 10 times every hour.