Reverse flow in isolation room

[seanhkim]

I'm evaluating isolation rooms in a hospital. The pressure difference between the room and the corridor is -0.0037"W (negative pressure) when the door is closed. But when the door is open, the pressure difference is getting reduced and surprisingly the pressure difference becomes postive. The corridor is CV - 1000cfm supply and 1000cfm return. The room is also CV - 200cfm return and 400cfm return.
Theoretically, the dP has to be zero when the door is open, but it should not reverse to the postive flow.
What would be the reason to explain this? And what would be
good remedies to keep the negative pressure difference all the time?

 

[BronYrAur]

Does the corridor "openly communicate" with another space? In other words, could there be a strong negative adjacent to the corridor that is making it negative even though the air system serving the corridor appears to be balanced? This is the only thing I can think of that would make the isolation room positive to the corridor.

Being a hospital (especially an isolation room) I assume that the returns are all ducted. I have had circumstances in plenum return buildings where opening a door changes air flow simply because the path of least resistance is through the door instead of through a ceiling grille into the plenum.

By the way, I assume you meant that the isolation room has 200 cfm supply.

 

[mechanicaldude]

This is the reason isolation rooms should have Ante Rooms. So you never have compromise the pressure relationships from the critical room to the corridors. If there are air born diseases in the the isolation room all that can potentially goes out the door into the corridor when the doors open up. If adding an Ante Room is not feasible than
why not maintain constant pressure differential under changing conditions by varying the exhaust-
supply flow differentials. ? Can you increase your exhaust air quantity in the room when the door is open to make the room even more negative?