Problem with simulation
Jeans Kim
I'm having trouble with the CONTAM simulation as shown in the attachment.
In the attached project file 'sample_shaft_press.prj',
path(55), path(57) and duct(17) on the bottom level are connected to the same pressurized shaft.
Relative elevations of the paths and duct are all set to 1 m.
However, the result pressures that appear on paths and duct are very different.
Pressure on the path is over 10 Pa, on the duct system is under 1 Pa.
What is the reason?
Thank you in advance for your help.
Jeans
Dols, William Stuart (Fed)
Jeans,
Let’s look at an easier example to illustrate your “problem”.
The attached example shows the effect that stack pressure has on the resultant pressures.
It is meant to illustrate the point that pressure at elevation is reduced from the zone reference pressure by rho * g * h.
Please review the attached PRJ and spreadsheet.
You can modify the elevation of the flow paths/terminals and temperatures of the zones (indoor and/or outdoor) to observer variations in resultant flows/pressures.
Note that during a simulation CONTAM creates implicit nodes (zones) for each duct terminal.
Also, each terminal experiences a pressure drop as presented in the spreadsheet.
I also used an orifice element in the ducts to simplify the airflow calculations, i.e., the orifice does not account for dynamic frictions losses as does the Darcy-Colebrook model.
I used the simread tool to obtain results provided in the spreadsheet.
This tool is available in the CONTAM installation folder.
- Stuart
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Dols, William Stuart (Fed)
Jeans,
Prompted by D.J. Lee's post (https://groups.google.com/a/list.nist.gov/g/contam/c/dLUEI0eI79I/m/DP4q1-tjAAAJ), I looked deeper into your issue.
It appears that the your PRJ file has some confounding issues associated with it.
The level data associated with the terminals in question (as well as some others) is incorrect.
The figure below shows the differences between your original file and that of the corrected file (I edited the PRJ with a text editor to correct the issue).
The column labeled “l#” should be the level number on which the junction resides in the PRJ.
The PRJ on the Right has the correct values, while the one on the left shows the original.
The level elevation along with the relative elevation of the junction is used to determine the overall elevation of the junction, thus leading to erroneous stack pressures.
The results from simread are shown below.
You can see the for the “fixed” case that path and duct pressure differences match as desired, but they do not for the original as you pointed out in your initial post.
NOTE: flows and dP are negative for flows into a terminal (from a zone) and positive for flows out of a terminal (into a zone).
My thanks to D.J. Lee for taking the time to address this issue!!!
And, my apologies for not addressing the issue properly in the first place.
Unfortunately, I cannot identify the reasons why such an error occurred in your original model.
I assume you used ContamW to create it.
I tried copying/pasting Terminal properties between floors, but I could not recreate the errors.
If you are able to isolate the cause of this I would appreciate you sending us the steps involved in doing so.
- Stuart