President

As industries and markets grow more competitive- and as the unarguable edict of energy conservation becomes widely accepted in all industries- it is necessary to re-evaluate existing methods of airflow design. Airflow rate in a cleanroom is the biggest factors affecting both the initial and operating costs of cleanrooms. The basis of cleanroom airflow design has not changed much over the past twenty years. In designing new facilities or upgrading existing ones, most cleanroom companies simply use design charts [1] (see Table 1) showing different air exchange rates and average room velocity for various classes of cleanrooms. These charts are often based on nothing more than mere opinions or on the simple fact that this is how rooms were designed in the past. Another design approach is to simply fix the filter velocity at 90 fpm 1 and then specify different ceiling coverage percentages for different classification levels. Experience has demonstrated that these methods are not efficient and, in many cases, result in over design or in problem installations. Further, these methods were "formulated " when most HEPA filters had a rated filtration efficiency of 99.97 % at 0.3 Um. Most terminal HEPA filters in use today have a filtration efficiency of 99.99 % at 0.3 Um. This is not an insignifican