Messy airflow design chart

10/01/2002

This letter is to comment on the July 2002 "Unfiltered" column "Cleanroom airflows Part II: The messy details" by Mike Fitzpatrick and Ken Goldstein.

I feel I must comment on the real "mess" concerning the Institute of Environmental Sciences and Technology (IEST; Rolling Meadows, IL) airflow "design" charts.

First of all, the authors should have provided a complete list of the important variables that affect airflow design. Secondly, a discussion regarding the importance of determining the airflow design and its impact on both initial project cost and operating costs is warranted.

The biggest drawback is the lack of open acknowledgement regarding the real problems concerning the IEST chart. There is no traceable technical basis to this and other similar charts, and the charts do not take into account the many variables that significantly affect cleanroom design—make-up airflow and concentration, filtration system efficiency, distribution of air into the room, the process generation rate including ingression of particles, etc.

This new chart also does not take into account the above-mentioned variables that should be involved in airflow design. We do not design air conditioning systems for cleanrooms without conducting calculations, so why should engineers base the most important design variable (that determines up to 40 percent of the cost of the cleanroom) on a questionable chart instead of doing engineering analysis?

It seems typical of such organizations to look only inwards; in this case, to address the considerable criticism mounting against the use of such charts. Certainly, non-IEST published information related to engineering design methods for airflow should have been at least referenced in the article. I am not suggesting that these published methods have a perfect design method, but certainly the methods presented have technical basis.

—Raj Jaisinghani
Technovation Systems Inc.