Air Changes Per Hour (ACPH)

Air changer per hour

What is ACPH?

Air Changes Per Hour (ACPH) is a critical metric used to quantify the rate at which the entire volume of air within a specific space or room is exchanged or replaced with fresh, clean, filtered air in one hour. For instance, an ACPH value of ’40’ means that the entire air volume within a room is completely refreshed with new, filtered air a staggering forty times in just 60 minutes.

It constitutes a foundational gauge across diverse sectors, encompassing pharmaceuticals, healthcare, electronics production, cleanroom technology, and the planning of HVAC (Heating, Ventilation, and Air Conditioning) systems. The significance of ACPH lies in its direct influence on the quality of air, the level of cleanliness, and the safety within a controlled setting.

ACPH = Air changes per hour

CFM= Cubic feet per minute


The required ACH can vary depending on the cleanliness class or classification of the cleanroom, which is determined by the industry and specific application. Here are some general guidelines for ACH in cleanrooms based on ISO standards:

  • ISO 14644-1: This standard provides cleanliness classes for cleanrooms, and it is commonly used as a reference for ACH requirements. The ACH requirements vary depending on the class, with higher classes requiring more frequent air changes to maintain cleanliness.
  • USP 797 and USP 800: These are guidelines provided by the United States Pharmacopeia for pharmaceutical compounding cleanrooms. USP 797 outlines ACH requirements for sterile compounding areas, and USP 800 specifies ACH requirements for hazardous drug compounding areas.
  • GMP (Good Manufacturing Practice): ACH requirements for cleanrooms in the pharmaceutical industry are often determined by GMP regulations, which can vary by region and country. These regulations may specify ACH based on the type of operation being conducted.

The Role of ACPH

Air Changes Per Hour is of paramount importance in cleanrooms, where stringent environmental control is necessary to prevent contamination and maintain important levels of cleanliness. Here’s why ACPH is crucial in cleanroom environments:

  • Contamination Control: Cleanrooms are designed to limit particulate and microbial contamination to protect sensitive processes and products. Air Changes Per Hour ensures a constant flow of clean, filtered air into the cleanroom, reducing the concentration of airborne contaminants. This frequent air exchange helps maintain the required cleanliness levels for various cleanroom classifications, as defined by ISO standards.
  • Particle Removal: Particles in the air, even those invisible to the naked eye, can compromise the quality and integrity of products manufactured in cleanrooms. ACPH plays a vital role in removing these particles by continuously cycling in fresh, filtered air. Higher ACPH values result in more effective particle removal, which is crucial for industries like semiconductor manufacturing and pharmaceutical production.
  • Temperature and Humidity Control: In addition to cleanliness, some cleanrooms require precise temperature and humidity control. ACPH assists in distributing conditioned air evenly throughout the cleanroom, helping maintain the desired environmental conditions.
  • Worker Safety: Cleanrooms may be used for hazardous processes or materials, such as those involving toxic chemicals or biohazardous substances. Sufficient ACPH helps protect workers by continually diluting and removing potentially harmful substances from the air.
  • Product Quality and Yield: In industries like semiconductor manufacturing and biotechnology, where product quality is critical, ACPH contributes to consistent production outcomes. A clean and stable environment with the right ACPH minimizes the risk of defects and ensures high product yields.
cleanroom airflow test

Factors Influencing ACPH

Several factors influence the calculation of ACPH:

  • Room Size: Larger cleanrooms typically require more air changes to maintain uniformity in air quality.
  • Type of Product and Industry: Industries such as biotechnology, semiconductor manufacturing, and pharmaceuticals demand elevated cleanliness standards, necessitating correspondingly higher ACPH values.
  • Cleanliness Level: The industry and the class of cleanroom (ISO Class 1 to ISO Class 9) will determine the required ACPH.
  • Processes: Certain processes generate more contaminants, necessitating higher ACPH to maintain desired cleanliness levels.
  • HEPA/ULPA Filters: The efficiency of air filtration systems plays a significant role. High-efficiency filters can reduce the required ACPH.
  • Personnel: The number of personnel working in the cleanroom can contribute to particle generation and influence ACPH calculations.

Air Changes Per Hour (ACPH) is a critical metric for maintaining the purity and precision of cleanrooms. It is a testament to the commitment of industries to meet stringent quality and safety standards. Understanding the specific ACPH requirements for your cleanroom is essential for ensuring the integrity of your processes and the reliability of your products. As technology continues to advance, the optimization of ACPH will remain central to the evolution of cleanroom technology, enhancing the capabilities of industries that rely on these controlled environments.

Planning to design a cleanroom with a well-balanced Air Changes Per Hour (ACPH) and require expert assistance, please do not hesitate to contact us. We are here to help you create a cleanroom environment that meets your specific needs and cleanliness requirements. Contact us now for a consultation!

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