Concerned about possible cross-contamination between different cleanliness classes within a cleanroom garment changing area, Alcon's own in-house engineering team employed Flovent to carry out a design study simulating air movement, heat transfer, and distribution of contaminants throughout the rooms.
The layout of the area affected comprised an unclassified area, where technicians changed from their laboratory clothes into their cleanroom garments. Then, depending on what they were working on, these technicians passed through areas C or D - area C offering the highest level of cleanliness and D the lowest.
The original ventilation system design utilized 12 standard ceiling mounted HEPA filters, supplying clean air, which was then removed via low-level extracts in the unclassified area. The results of the Flovent model clearly showed the deficiencies of this design strategy with contaminated air flowing from the dirtier to the cleaner areas of the room.
Engineers from Alcon took the data from this first study and used it as the basis for a design study, simulating a series of "what if' scenarios and comparing their performance with the baseline computer model.
Through this parametric design study, aimed at assessing the sensitivity to change of the ventilation scheme, a final, improved design evolved which performed very differently to the original concept. In the first instance, a floor to ceiling partition wall was installed between the unclassified area and the Class C area, providing a physical barrier to airflow between these zones.
High capacity HEPA filters, combined with a CG cloth, were installed above the doors entering the Class C production areas which created a unidirectional air-flow. The HEPA filters across the remainder of the room were replaced with high capacity HEPA filters connected to two ceiling mounted air socks creating a radial pattern of airflow dispersal.
Predictive airflow modeling indicated the success of this installation, with the air flowing from the cleanest areas in the room back towards the low level extracts in the unclassified area thus preventing cross-contamination. Alcon engineers subsequently validated these airflow predictions by performing a series of actual smoke tests prior to final commissioning of the premises.
Using Flovent, Alcon's engineers were able to model and test unconventional design concepts, to see how they met cleanroom regulatory requirements and to make cost-effective design changes extremely quickly. There is little doubt that without this simulation work, the installation would have gone ahead with the original design and potentially serious problems when it came to commissioning and validation of the room. Commenting on the design study, Michel Wellens, project manager at Alcon Belgium, said, "The investment made in this design study has more than paid for itself. The money and time saving made in avoiding design changes in the final stages of the project means that we have finished with a robust reliable design that was proved to work as intended at the conceptual design stage of the project".
Flovent has been developed in close collaboration with the Building Services Research and Information Association. This is the UK's center of expertise for heating, ventilating and air conditioning. The result of this collaboration is a powerful, yet easy-to-use, software program that does not require a specialist knowledge of fluid dynamics. In providing a fast, cost-effective method of design evaluation, Flovent can be used to improve ventilation performance, whilst minimizing the need for costly on-site modification.
Further information on Flovent can be obtained from Flomerics Inc., 257 Turnpike Road, Southborough, MA 01772; 508-357-2012; 508-357-2013 (fax); firstname.lastname@example.org; www.flovent.com.