Smokeview file not found and HVAC problem

[Torbjørn Knutson]

Hi.

I have two problems, which I hope some of you can help with:

First and foremost: When I try to run the FDS-simulation, it states: ***Error: Smokeview file, ss1.smv, not found

I'm worried that the model is too complex, but in that case, how can I be sure?

The second problem is a peculiar one: I have attached nodes to one (1) duct and specified their coresponding vents. The program even has a help function that states that only one duct can be attached for this function. Trying to run the simulation, it states that the follwing: "internal DUCTNODE" must have at least two attached ducts".

Thanks for your time,

Torbjørn

[dr_jfloyd]

Please attach the fds file not the Pyrosim file.

[Torbjørn Knutson]

Aaah, sorry. There you go.

Torbjørn

[dr_jfloyd]

&HVAC ID='Node148', TYPE_ID='NODE', DUCT_ID='Duct','Duct30','Duct31','Duct32','Duct33','Duct34','Duct35','Duct36','Duct37','Duct38', XYZ=47.3404,22.6014,11.6503/

For every duct in this input you specified a fixed volume_flow of 0.444444 into the node.  This is non-physical.  you can't flow 4 m^3/s into a node and flow 0 m^3/s out.

Same for the other lines which are similar

All of your HVAC vents are at Z=11.4003. With a quick scan of your inputs, I don't see any appropriate obstructions for those vents to attach to.  But your file is very complicated.  Double check that you have properly placed your vents and fix the ductnode definitions.  If you still have problems, simplify your input to the bare minimum needed to replicate the problem and post it.

[Daniel Swenson]

Torbjørn,

I did spend some time looking at your model and since the problems you had are fairly common, let me give a fairly detailed response. 

First, it is nice to see a model that is using HVAC in a fairly complex way. The attached model.png image shows an auditorium with several vents, fans, and ducts.

In order to debug the model, I simplified it to have only the middle distribution system and I removed most of the obstructions. This made it possible to focus on the HVAC components. 

The first major problem was with the central node that is intended to supply air to the vents. This node did not have an associated inlet vent. In addition, an endpoint HVAC node can only be connected to one duct. To fix this problem, I (1) added a vent on the top of the ceiling obstruction, (2) added an endpoint node at this vent, (3) added a duct connecting the original central node with the new inlet node. See the image endpoint_problem.png to understand the changes (this image does not show the new inlet vent).

The second major problem was due to the small outlet vents and the size of the mesh cells. FDS snaps all geometry to the grid. In the model, the outlet vents are small and positioned in the mesh in such a way that they will collapse to a point, so are not being included in the FDS model. To fix this, I made the outlet vents larger, see vent_problem.png. This error is fairly common. When deciding the size of the mesh cells, not only are there limits placed due to the desired flow accuracy, but there are also limits required to capture the level of desired geometric detail.

Some less critical problems and suggestions include:

 

1. To help understanding, I used the PyroSim Grouping option to organize the model.

2. You might want to consider multiple meshes and parallel processing

3. Deleted an extra Vent that was not attached to anything.

4. Changed all HVAC ducts to reference the HVAC fan

5. Reversed duct flow direction.

6. Added slice planes to see the velocity.

7. Cut off some of the mesh to make the problem run faster for debugging.

I made these changes to the simple debugging model. You will have to implement something similar in your more complex model. A short run using the simple model is shown in results.png. I have also attached the corresponding FDS and PyroSim files.

Hope this helps,

Dan Swenson, Thunderhead Engineering