Sea level effect in pressurization systems

[Alfredo Jara Munar]

Hi, 

My name is Alfredo, and I am a Peruvian consulting engineer in fire protection systems, and I’m in charge of the Smoke Control Department of the company i work from, and I'm glad to participate in this group. I've been recently using CONTAM in stariwell pressurization projects, and I find it very useful. 

I'm developing some projects of buildings that are going to be constructed at more than 3,500 meters above sea level, and I have some questions about this fact (sea level effect). 

According to the SFPE Handbook of Smoke Control Engineering, with low atmospheric pressure (high sea level), it is required more flow rate than in a low sea level building, in order to accomplish a determined pressure difference between the stair and the building. When I put the sea level in CONTAM, the results are different, because it is needed less flow rate in a building at a high sea level. 

My question is, why does this happen? Is there something I am not considering? These are the formulas that SFPE Handbook consider, and explain that it is needed more flow rate in order to accomplish a determined differential pressure. I attach also the file in CONTAM in order to have a review of this fact. I’d be grateful to solve this, thanks a lot for your time.

 

 

 

 

 Regards,

Alfredo Jara Munar
Mechanical Engineer
+51 961 810 960

[William Dols]

CONTAM reports airflows as mass flow rates at standard density.

You can see the ambient density (that at which the Simple AHS is providing airflow) when you move the cursor to the ambient zone on the SketchPad.

See this conversation for more information.

https://groups.google.com/a/list.nist.gov/g/contam/c/ZkuoynMP7Bs/m/Kupo29hJAwAJ

You can also use a Constant Volume Flow element to pressurize the shaft, either by incorporating it into a duct system or by connecting the stair shafts directly to the outdoors or via an intermediate zone.

- Stuart

[Alfredo Jara Munar]

Hi William,

thanks for your answer. The problem is that, by hand calculations, I need more flow rate at high sea level than a low sea level, in order to accomplish a determined differential pressure. This has sense because the formula stablished in the Smoke Control Engineering Handbook. In CONTAM, you can put the weather data, but when the software simulates it, the result is different. Why does this happen?

Thanks a lot again, best regards,

Alfredo Jara Munar

[Dols, William Stuart (Fed)]

Alfredo,

I’m not sure if you’ve resolved your issue, but when I run your model HIGH (3859 m) vs LOW (0 m elevation) I get the results provided in the attached spreadsheet which reveals a higher volumetric flow rate (but lower mass flow rate) is required to achieve similar results (based solely on looking at pressure differences across the SINGLE_DOORs of ESCALERA2). The “Adj” case was simulated by using a schedule to reduce all the supply flows by the same fraction.

 

 

The spreadsheet and accompanying PRJ files also provide a demonstration case based on simple stack theory.

I am not sure what “hand” calculations you are using, so please elaborate if the above does not satisfy your questions.

 

- Stuart

 

From: con...@list.nist.gov <con...@list.nist.gov> On Behalf Of Alfredo Jara Munar
Sent: Monday, November 17, 2025 8:27 PM
To: CONTAM <con...@list.nist.gov>
Cc: Dols, William Stuart (Fed) <willia...@nist.gov>; alfredo...@gmail.com <alfredo...@gmail.com>
Subject: [EXTERNAL] [contam] Re: Sea level effect in pressurization systems

 

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 Regards,

Alfredo Jara Munar
Mechanical Engineer
+51 961 810 960

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