Modeling Non-Homogeneous Leakage in Ducts Using CONTAM

[Anaïs EMERY]

Hello,

My name is Anaïs, and I am currently working on modeling ventilation ducts using the CONTAM software.
Specifically, I am trying to represent non-homogeneous leakages within the ducts.

In this context, I have tested several approaches, but it seems that such leakages cannot be directly modeled in CONTAM.
The first approach I explored was to divide the ducts using junctions and adjust the length of each segment to represent areas with varying leakage levels.
The second approach was to model a leakage as an unbalanced terminal, using a very short adjacent duct segment (set to 1e-5 m based on my tests).

I would appreciate your opinion on the viability of these methods, or any suggestions for alternative approaches.
In particular, I would like to know whether it is possible to control leakage parameters via controllers, in order to simulate, for instance, a duct outlet with a certain number of potential leak locations and a program that randomly determines the number and position of active leaks among them.

Thank you very much in advance for your time and insights.
Best regards,
Anaïs

[William Dols]

Anaïs,

You can use multiple approaches, depending on your analysis requirements and the available input data.
CONTAM provides duct leakage information based on leakage classification, as per the duct design information provided in the ASHRAE Handbook of Fundamentals.
The simulation of duct leakage using this method is described briefly in the Defining Duct Segments section of the CONTAM User Guide:

As previously mentioned, duct flow elements contain duct leakage information. The CONTAM model implements all leakage at the junctions and terminals of a duct segment. This means that half of the leakage associated with a duct segment occurs at each end of the segment. The leakage between a junction and the zone in which the junction is located (as determined on the SketchPad) is a function of the duct element leakage characteristics and the pressure difference between the junction and the zone. You should consider this leakage model when accounting for leakage of a duct that passes through multiple zones. You should put at least one junction (or terminal) in each zone within which you want to account for duct leakage.

You could also proceed, as you mentioned, by defining a terminal within desired zones that represent duct leakage based on, for example, an orifice element defined within the associated duct segment.
You could also utilize Simple Air-handling Systems and specify exact flow rates to represent terminal and leakage flows within desired zones.

Duct segments can be controlled if using elements other than the Darcy-Colebrook element, e.g., orifice elements may be controlled, and terminals can be controlled based on their loss coefficients as explained in the Theoretical Background - Airflow Analysis - Duct - Terminal Loss Calculation section of the User Guide.

You could also utilize parametric analysis to generate PRJ files, for example, using the capabilities provided by NIST here: https://www.nist.gov/el/energy-and-environment-division-73200/nist-multizone-modeling/contam-parametric-analysis.

I would suggest starting with simple models to gain an understanding of the various capabilities and their associated advantages and disadvantages in relation to your needs.

Happy Modeling,

Stuart