[Sávio Almonfrey]

Dear CONTAM Support Team,

I am currently developing a pressurized stairwell model using CONTAM and would like to clarify the behavior of the “Balance Loss Coefficient” feature.

In my model, I defined multiple duct terminals and enabled the “Balance Terminal” option, assigning a design flow rate to each terminal in order to achieve a uniform airflow distribution.

After applying the balancing command, I observed that the expected adjustment did not occur. The “Balance Loss Coefficient” (Cb) remained equal to zero for all terminals, and the airflow rates were not corrected to match the specified design values.

For example, in one of the terminals:

• Desired flow rate: 0.083 m³/s
• Actual flow rate (without balancing): approximately 0.30–0.44 m³/s (terminal closest to the ground floor)

Even after applying the balancing command, the software did not modify the Cb value, and the system continued to operate with airflow rates significantly higher than the desired values.

On the other hand, when I manually assign a Balance Loss Coefficient, the airflow adjusts correctly to the target value. However, performing this adjustment manually requires multiple iterations and trial-and-error, making the process inefficient.

Therefore, I would like to clarify:

1. Under what conditions is the Balance Loss Coefficient effectively calculated and applied?
2. Are there specific requirements for the duct network in order for the balancing function to work properly?
3. Is there a recommended procedure to correctly execute the balancing process?

Thank you in advance for your support.

Best regards,

Domingos Sávio Almonfrey - Firefighter

[William Dols]

If you really want the desired flow rates at each terminal, then you may want to just use a simple Air Handling system and specify the desired flows.

If you really desire to balance the duct system, then you proceed as follows:

1. Fix the terminal on Level <25> to be included in the balancing.
2. Reset the default project temperature to 20 C (via View -> Project Options dialog) => set all zone, junction, and terminal temperatures to 20 C.
3. Process the duct system in isolation from the building leakage by defining the Vaz-parede element to be large, e.g., 10 cm2/m2. The leakage values for your openings appear to be very tight. This makes it difficult to obtain proper flow directions during the balancing. There are also no interfloor leakages between zones other than the ESCADA zones. I added some to the attached models.
   NOTE: You may need to run the balancing twice to achieve convergence. Accept the coefficient modifications and flow adjustment, then simply rerun the balancing.
4. Once balanced, you can reset the Vaz-parede leakage back to 1 cm2/m2 and see that the building leakage prevents achieving the design flows. 
5. Rerun the balancing, and you should be able to achieve the design flows.

See attached files for the cases I used.

- Stuart

[Sávio Almonfrey]

Dear Willian Dols,

Thank you very much for your detailed response and for taking the time to analyze my model. Your explanation helped me understand the balancing process much better.

I did not use the “simple Air Handling system” because my objective was to dimension the duct system simulating a real stair pressurization system, including the pressure losses along the ducts and terminals.

I also realized that my mistake was related to the balancing procedure itself. I was not actually running the balancing command properly. I thought that simply enabling/configuring the balancing option would already make CONTAM automatically perform the balancing calculation, but now I understand that I must explicitly execute the balancing process, and in some cases rerun it for convergence.

Your comments about the leakage paths and the “Vaz-parede” values were also very important and clarified why the system was struggling to achieve the desired flow directions and design flows.

Thank you again for your support and for the attached files. They were extremely helpful for my understanding of the model behavior.

I would also like to ask a few additional questions:

When I use a constant flow ventilation system in CONTAM, can I directly obtain enough information to select a real fan (for example airflow and required pressure)? Or would the actual fan selection only be properly performed by inserting and analyzing a fan “performance curve” inside CONTAM?

In addition, to model a gravity pressure relief damper in a pressurized stairwell, would the best approach be to use the “self-regulation vent” component?

My objective is to maintain the stair pressure differential below a maximum value of approximately 80 Pa, for example.

Best regards,

Domingos Sávio Almonfrey
CBMES