Controlling room pressure is only one aspect of cleanroom facility design when creating segregated zones of different class. A broader view based on designed airflow rather than mere room pressure has many benefits, argues Frans Saurwalt of Kropman Contamination Control.
Specifying room overpressure in cleanroom design is a common contamination control concept. To achieve this the HVAC needs to be designed to control the room pressure by some means. Most commonly this is achieved using pressure controlled actuated dampers in the return ducting. These dampers have to be designed to modulate within a certain airflow range and with a specific accuracy and speed of reaction. Understanding the mechanisms that will create a room pressure, as well as those factors that challenge it, is essential for success. Cleanrooms designed for ‘containment’, i.e. intended to keep specific contaminants in, are not in the scope of this article.
To understand the principles governing room pressurisation, consider first a room being within the envelope of a general building. This room will have the same pressure as the surrounding environment as the construction is usually far from airtight.
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