Cleanroom Air Changes Guidelines
Air changes per hour (ACH) is a measure of how many times the air in a cleanroom is replaced by filtered air in one hour. ACH is an important factor for determining the cleanliness level and energy efficiency of a cleanroom. The higher the ACH, the more filtered air is supplied to the cleanroom, which reduces the concentration of airborne particles and contaminants. However, higher ACH also means higher energy consumption and operating costs for the cleanroom.
There is no universal rule for how many air changes per hour are required for different cleanroom classifications. Different standards and guidelines may have different recommendations based on the application, process, and product requirements. However, some general ranges can be found in the literature and industry practices. For example, according to the ISO 14644-1 standard, the following table shows the approximate ACH ranges for different ISO classes:
The table above is based on the assumption of unidirectional airflow, which is a type of airflow that flows in a single direction with a steady velocity and parallel streamlines. Unidirectional airflow is typically used for cleanrooms with higher cleanliness levels (ISO 5 or better), where laminar flow is required to minimize turbulence and particle suspension. For cleanrooms with lower cleanliness levels (ISO 6 or worse), turbulent airflow may be used, which is a type of airflow that flows in a highly random motion and creates mixing and dilution of particles. Turbulent airflow may require lower ACH than unidirectional airflow to achieve the same cleanliness level, depending on the design and layout of the cleanroom.
The ACH for a specific cleanroom should be determined by a careful analysis of the factors that affect the particle generation and removal in the cleanroom, such as:
• The size and layout of the cleanroom
• The number and type of equipment and personnel in the cleanroom
• The sources and rates of particle generation and emission in the cleanroom
• The type and efficiency of the air filtration system
• The type and direction of the airflow pattern
• The temperature and humidity conditions in the cleanroom
• The product and process specifications and requirements
The ACH for a cleanroom should be optimized to achieve the desired cleanliness level while minimizing the energy consumption and operating costs. ACH should not be too high or too low, as both extremes can have negative impacts on the cleanroom performance and efficiency. Too high ACH can cause excessive noise, vibration, and pressure drop, as well as increased energy use and carbon footprint. Too low ACH can cause insufficient particle removal, poor air distribution, and increased risk of contamination and cross-contamination.
To determine the optimal ACH for a cleanroom, it is recommended to consult with a professional cleanroom designer or engineer who can perform a detailed analysis and simulation of the cleanroom system and provide a customized solution that meets the specific needs and goals of the cleanroom application.