Space pressurization is well-known as a tool for control of air contaminants and a standard building block of laboratory ventilation systems. Several methods are in common use; steps to design, implement and commission them are widely published. Among those familiar lessons is the fact that the tightness or leakiness of the room envelope significantly affectsthe operation of the pressurization system.

When the room is sealed, or nearly sealed, mechanical coupling between air flows in and out of the room complicates control loop dynamics Flow and pressure loops that are ordinarily almost independent become tightly coupled with the potential todestabilize one another.

This paper develops the mathematical models that support analysis of a pressurization control system. The effect of mechanical parameters, especially the envelope leakage as it ranges from tight to effectively zero is exposed for study.