TECHNICAL FEATURE only in the close vicinity of the sources of particles (operators). A comparison of the Spread Index analysis between the 40 ach (Figure 5) with the modifi ed diffuser layout with 25 ach (Figure 9) shows not only the reduction in the SI values but also qualitative improvement showing reduced spread in the vicinity of the isolator. These conclusions are contrary to the popular belief that simply increasing the ach can improve the cleanliness levels. These analyses indicate that proper location of supply diffusers is crucial for improving the effectiveness of the supply air in removing the contaminants from the critical zones of a cleanroom. These fi ndings are similar to the previous analyses.11,12 Summary and Conclusions Pharmaceutical cleanrooms are used for the manufacturing of drugs and medical products and require a high level of cleanliness to maintain the aseptic environment. Often high air changes per hour (ach) are specifi ed to ensure a higher level of cleanliness. Such specifi cations are often based on engineering judgment, assume well-mixed indoor environmental conditions and target a certain average value for the particle concentration in a cleanroom. However, in reality, the cleanroom indoor environment is seldom well-mixed with nonuniform distribution of particles. Airfl ow patterns play a crucial role in determining the level of nonuniformity and cleanliness levels in the critical zones of a cleanroom. Several interrelated factors can affect the airfl ow patterns and resulting fl ow path of airborne contaminants. This CFD study systematically evaluates the impact of ach and the locations of supply diffusers on the airfl ow patterns and the resulting distribution of particles in the critical zone of a pharmaceutical cleanroom. Spread Index-a CFD-based metric-is used to compare the contamination control performance for three levels of ach and two different layouts of laminar diffusers. These analyses indicate that the airfl ow patterns are mostly non-unidirectional and independent of the ach Faster. Easier. Safer. INNOVATIVE CAPTURE HOODS 15 " 3# Ultralight Desiccant and Energy Recovery wheels available in standard and custom sizes. Call or email us for a quote today! 100-2500 CFM 30-3000 CFM 15-150 CFM * Magnet frames * No air gaps * View up to 4 hoods simultaneously * Custom skirts available Innovative Tools for Temperature and Humidity Meter-Sensor for Temperature & Humidity can be used with or without Wrist Reporter *Temp and Humidity Probes Available in 5 " , 12 " , and 24 " info@rotorsource.com | www.rotorsource.com 225 -753 1700 225 -753 -1 *Interchangeable with all Evergreen T&H Probes A U G U S T 2 0 2 3 ashrae.o rg ASHRAE JOURNAL 47 8 "http://www.rotorsource.com https://ashrae.org/