Help with Differential Pressure Reference

[ksechler]

We are doing a startup of a new biotech facility. We are monitoring (but not controlling) differential pressure. This is done by installing a single DP instrument for each room of interest and referencing it back to a common header. Then interelationships can be figured arithmatically in the building management system to determine DPs between rooms. Unfortunately, our header seems to be building some pressure (positive at times and negative at others). It is vented to the outside via a specialty diffuser (which is supposed to eliminate wind effects). I wouldn't care so much about the offset, but it is not uniform. Does anyone have experience with similar systems so we can compare notes. This is my first pass at using a common reference header like this, and until I resolve it the outputs from the DPM's are essentially crap.

 

[quark]

Just a blind idea. Check the pressures of the rooms with and without diffuser. It may be possible that when you fit the diffuser at the end of the atm. header and then you are plugging in the other ends to pressure indicators, the header after the diffuser may be balanced by room air rather than atmospheric air (because the least resistance path for air is from rooms into the header rather than from atmosphere---->diffuser--->header.

As you have different pressures in different rooms, there may be a possibility that the header might experience differet pressures.