Letters

04/01/2003

The AC/H debate continues

The article by Fitzpatrick and Goldstein ("Cleanroom airflow: Issues other than cleanliness often drive HVAC design," page 10, CleanRooms, March 2003) states that often it is the sensible heat load that controls the amount of airflow rate necessary for cleanroom design than the required airflow for cleanliness.

While this may be true for a few ISO Class 7 and 8 rooms, it is almost impossible for ISO Class 1 - 5 rooms. Even for ISO Class 7 and above rooms, this may be only true for the central air-handling systems where all the flow is processed through the air conditioning unit.

In my experience with the more efficient distributed air handling system, this condition almost never arises. My experience is that cleanroom airflow design is more often inefficient, irrespective of the sensible heat requirements, simply because the IEST and other airflow charts used for determining air changes per hour do not have a technical basis or foundations.

Raj Jaisinghani
President, Technovation Systems, Inc.