System Node Pressure Question

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I'm trying to calculate the energy impacts of the damper leakage limitations in ASHRAE 90.1. To do this I'm trying to better understand the pressure differential across exhaust and intake dampers using EnergyPlus.

I'm reporting the following variables

1. Outdoor Air Stream Node Air Pressure
2. Relief Air Stream Node Air Pressure
3. Mixed Air Node Air Pressure
4. Outdoor Air Pressure
5. Return Air Stream Node

as expected (1) and (4) are pretty much identical (+/- 1%, which i assume is due to interpolation). (5) is equal to (2) and they are both a constant 99716.667 Pa at every timestep all year and (3) varies when the system is on as one would expect.

so, my questions are as follows:

Why are (5) and (2) constant and where does that value come from?

If the system's outdoor air and exhaust dampers are closed but the system is running, which nodes should I use to calculate pressure differential(s) to use for estimating air leakage?

Will I need to use an airflow network to make this all work out properly?

Thanks.