Cleanroom Air Changes Per Hour (ACH):

By Deiiang™ Cleanroom Solutions | Product Designer: Jason.peng

What is Cleanroom Air Changes Per Hour (ACH)?

Cleanroom Air Changes Per Hour (ACH), also known as the air exchange rate, is a critical metric that quantifies how often the entire volume of air within a cleanroom is replaced with newly filtered and conditioned air every hour. It's calculated by dividing the total volume of air supplied to the cleanroom per hour (often measured in cubic feet per hour or cubic meters per hour) by the total cubic volume of the cleanroom itself. This rate is a direct indicator of the cleanroom's ventilation system efficiency in refreshing its internal atmosphere.

The significance of ACH in cleanrooms stems from its direct impact on contamination control. By facilitating a continuous and rapid exchange of air, a high ACH rate ensures that airborne particulate matter, microorganisms, and other pollutants are effectively diluted and removed from the environment. This constant replenishment of clean air is fundamental to maintaining the stringent ISO cleanliness classifications required for sensitive manufacturing, research, and healthcare processes, thereby protecting product integrity, equipment, and personnel from contamination.

How to Calculate Cleanroom Air Changes Per Hour (ACH)

Accurate calculation of Air Changes Per Hour requires precise measurement of room volume and airflow rates. The fundamental formula for determining ACH provides the foundation for cleanroom design and validation.

ACH Calculation Formula

ACH = (Total Supply Airflow ÷ Room Volume)

Where airflow is in m³/h and volume in m³

Practical Calculation Example

Consider a cleanroom with dimensions 10m × 8m × 3m (L×W×H) and total supply airflow of 7,200 m³/h:

Room Volume = 10 × 8 × 3 = 240 m³
Total Supply Airflow = 7,200 m³/h
ACH = 7,200 ÷ 240 = 30 air changes per hour

This Air Changes Per Hour calculation confirms the cleanroom meets ISO 7 classification requirements according to Deiiang™ design standards.

Regular verification of ACH calculations ensures ongoing compliance and identifies potential system degradation. Jason.peng emphasizes that proper Air Changes Per Hour documentation forms an essential component of quality management systems.

Cleanroom Classification Standards and Recommended ACH Values

Industry standards provide guidelines for appropriate Air Changes Per Hour ranges based on cleanroom classification. Understanding these requirements ensures proper design and operation of controlled environments.

ISO Classification	Particle Count (≥0.5μm)	Recommended ACH Range	Typical Applications
ISO 5 (Class 100)	3,520	240-600+	Pharmaceutical filling, semiconductor
ISO 6 (Class 1,000)	35,200	90-180	Medical device manufacturing
ISO 7 (Class 10,000)	352,000	30-60	Compounding pharmacies, electronics
ISO 8 (Class 100,000)	3,520,000	10-25	Packaging areas, assembly

The recommended Air Changes Per Hour ranges account for factors like personnel density, process contamination, and equipment layout. Deiiang™ design protocols emphasize that final ACH determination should always include particle count verification.

Key Factors Influencing Cleanroom ACH Requirements

Multiple variables impact the optimal Air Changes Per Hour for any given cleanroom application. Understanding these factors enables more precise system design and operational control.

Personnel Density

Each person generates 100,000-1,000,000 particles/minute, increasing required ACH

Process Contamination

Manufacturing operations may require 15-30% higher Air Changes Per Hour

Room Configuration

Complex layouts may require customized ACH calculations for different zones

Equipment Load

Heat-generating equipment affects airflow patterns and ACH effectiveness

Proper assessment of these variables ensures appropriate Air Changes Per Hour specification. Deiiang™ engineering analysis typically identifies 3-5 key factors that significantly influence ACH requirements in any given application.

Measuring and Monitoring Cleanroom ACH

Accurate measurement of Air Changes Per Hour requires proper instrumentation and methodology. Regular monitoring ensures consistent cleanroom performance and early detection of system issues.

Primary Measurement Methods

Air Velocity Method

Measure velocity at multiple points, calculate average, multiply by outlet area

Flow Hood Measurement

Direct measurement using calibrated flow hood for accurate volume determination

Tracer Gas Analysis

Advanced method using gas concentration decay for precision validation

Regular verification of Air Changes Per Hour should occur quarterly or following any significant system modifications. Jason.peng recommends implementing continuous monitoring systems for critical environments where consistent ACH maintenance is essential.

Risks of Improper ACH: Understanding the Consequences

Both insufficient and excessive Air Changes Per Hour levels present significant risks to cleanroom operations. Understanding these risks informs proper system design and operational protocols.

Insufficient ACH Risks

Particle accumulation exceeding ISO classification limits
Increased product contamination and reduced yield
Regulatory non-compliance and audit failures
Cross-contamination between processes or products

Excessive ACH Risks

Unnecessary energy consumption (30-60% higher costs)
Increased filter replacement frequency and maintenance
Potential airflow turbulence disrupting contamination control
Reduced equipment lifespan due to constant high operation

Regular assessment of Air Changes Per Hour performance helps identify and mitigate these risks. Jason.peng emphasizes that proper ACH validation should occur during commissioning and at regular intervals throughout the facility lifecycle.

Frequently Asked Questions About Cleanroom ACH

Q: How often should ACH be measured in a cleanroom?

A: Quarterly measurements are recommended for most applications, with continuous monitoring for critical environments. Deiiang™ protocols include semi-annual comprehensive validation.

Q: Can ACH be reduced during non-operational hours?

A: Yes, with proper validation. Many facilities implement 30-50% ACH reduction during unoccupied periods, achieving significant energy savings while maintaining integrity.

Q: What's the relationship between ACH and airflow velocity?

A: ACH represents air replacement rate, while velocity describes air movement speed. Both parameters must be optimized for effective contamination control in cleanroom environments.

Comprehensive Cleanroom Solutions: Design, Validation, and Optimization