Sorry for the ambiguity.
Specifically, the pressure difference between the stair and the outside, at the bottom of the stair, (DPsob), is 8.7 in. of water. I was shooting for something in the neighborhood of 0.05 in. of water. This pressure difference is eventually used to calculate the flow...
I'm designing a stair pressurization system for an existing facility that is largely underground. My design occupant load is not decided on yet, so I am performing calculations in advance of this decision for two situations/assumptions: 1) all stair doors closed, and 2) some stair doors open...