Exhaust fans through exterior wall show 0 m³/s volume flow

[adrianeirom]

Hello,

I am working on a fire/smoke extraction model in PyroSim and I am having trouble getting my exhaust fans to actually extract smoke.

My system consists of four exhaust fans installed directly through an exterior wall. There are no ducts. The intended flow path is:

Interior → exhaust fan → exterior → open boundary

The exterior wall is approximately at Y = 38.0–38.2 m and has Allow Vents enabled.

For example, one of my exhaust vents has:

X = 64–66 m
Y = 38.0 m
Z = 5–7 m
Area = 4.0 m²
Normal direction = +Y
Surface type = Exhaust
Volume flow = 22.05 m³/s
Ramp-up = t² over 5 s
Activation is controlled by a PyroSim control

The vent is placed directly on the solid exterior wall.

I have also created a Volume Flow at a Boundary measurement at the same location (Y = 38.0 m, X = 64–66 m, Z = 5–7 m), with the wall-normal positive direction.

The problem is that when the exhaust fans activate, the measured volume flow remains essentially 0 m³/s. I only see very small fluctuations (around 0.007 m³/s), instead of something close to the specified 22.05 m³/s.

I have checked that:

The exterior boundary is open.
The wall allows vents.
The vent is located on the wall.
The vent has the Exhaust surface assigned.
The specified flow is positive (22.05 m³/s).
The fan activation control is working.
I have tried activating the fans from the beginning of the simulation as well.
I have checked the volume-flow measurement at the fan location.

My goal is simply to have the fans extract smoke from the interior and discharge it directly outside through the wall, without using ducts.

Could someone please help me identify what I am missing in the PyroSim interface or setup that prevents the exhaust vent from producing the specified flow?

I would especially appreciate a PyroSim GUI-based explanation, since I am setting everything up through the PyroSim interface.

I can provide screenshots of my wall, vent properties, exhaust surface, mesh boundaries and volume-flow measurement if needed.

Thank you!

[drjfloyd]

This forum does not provide Pyrosim support. For Pyrosim support contact Thunderhead Engineering.

[obscureed]

A flowpath starting at the interior doesn't make sense to me - to run continuously, the fans need to create throughflow. There needs to be a source of replacement air to the interior. I would expect that a leak-free space attached to powerful extract fans would become highly depressurised. I've done this by mistake, and usually FDS hits a numerical instability and/or complains about unrealistically low density.

[mcgratta]

If you think there is a bug, create a simple test case and start an issue. It's easier to track that way.

[obscureed]

I was just commenting on the OP's question, from a user's perspective. At first sight, I suspect a problem in the setup, not a bug.