Cross Sectional Area of Stair Shafts

[Marko Pilic]

Hello All, 

Question for defining the cross sectional area of the stair shafts. In the help guide of the CONTAM software the following is stated:

"Powerlaw Model: Shaft Cross-sectional area: This is the horizontal, cross-sectional, area of the shaft, not the opening."

In my case I have a closed stair well with a filled in stair shaft. Would the cross sectional area just be the stair shaft opening less then filled in stair shaft? 

Thanks, 

Marko 

[William Dols]

Hello,

I'm not exactly sure what you mean by "filled in stair shaft."
CONTAM does provide a "Stairwell" model that allows you to describe the cross sectional area of the associated stair shaft and whether or not the stair treads are open or closed.
If in fact you have some sort of shaft that has been "filled in" to significantly reduce the horizontal cross sectional flow area of the shaft, i.e. the area through which vertical flow occurs, then you might just create an orifice with the equivalent net remaining flow area.
You can search the User Guide for "stairwell" and "shaft" to find more information such as is provided in Section 4.2 "Special Applications of CONTAM - Smoke Control Systems."

- Stuart

[Marko Pilic]

Thank you William, 

What you have pointed out is correct, the stair shaft: the area through which vertical flow occurs, is in fact filled in. In this scenario, the air has to flow past closed stair treads to pressurize the stair shaft volume. How would one tackle this condition to accurately represent the net remaining flow area? 

Thank you, 

Marko 

[Marko Pilic]

William, 

I want to clarify my point above with the image below: The 32m2 area is the cross sectional area of the entire stair shaft, in red. The 8m2 area is the stair eye shaft, in blue, which is filled in in this case. This is what I was referring to when I said filled in stair shaft. It's the 8m2 section that's filled in. Is the CONTAM cross sectional area, of the stair model, just 32-8m2 = 25m2? 

Thank you, 

[Dols, William Stuart (Fed)]

The stairwell airflow element is based on measurements performed in the paper referenced within the CONTAM manual (ACHAKJI, G. & TAMURA, G. T. 1988. Pressure drop characteristics of typical stairshafts in high-rise buildings, National Research Council Canada, Institute for Research in Construction). This paper does not address stairwells of this configuration.

 

You might consider bracketing the problem to investigate the difference in resulting airflows and pressures obtained for the two areas you mention.
The differences will also be dependent on the resistance to flow of the stairwell relative to the walls and doors of the stairwell.

 

If, in fact, you have some measured data, then this could help you to finalize your decision.

 

- Stuart

 

From: Marko Pilic <mpili...@gmail.com>
Sent: Wednesday, August 2, 2023 12:34 PM
To: Dols, William Stuart (Fed) <willia...@nist.gov>
Cc: CONTAM <con...@list.nist.gov>
Subject: Re: Cross Sectional Area of Stair Shafts

 

William, 

 

I want to clarify my point above with the image below: The 32m2 area is the cross sectional area of the entire stair shaft, in red. The 8m2 area is the stair eye shaft, in blue, which is filled in in this case. This is what I was referring to when I said filled in stair shaft. It's the 8m2 section that's filled in. Is the CONTAM cross sectional area, of the stair model, just 32-8m2 = 25m2? 

 

Thank you, 

[Marko Pilic]

Hello Stuart, 

I have reviewed the NRC publication referenced in your e-mail and have the following question/comments: 

1. The stair shaft I am working with is not representative of the CONTAM model because it does not have an orifice area, through which vertical flow can pass through the stair shaft. Is that correct? 

2. Can you expand on your suggestion of bracketing the problem? I am unclear how studying the two different areas can lead to anything meaningful. 

3. I don't have any measured data which could help to inform the analysis I am performing. 

I know for certain that the airflow volume and pressure drop will be increased, in my stairwell scenario. That being said, I am at a loss of how to quantify the additional volume and pressure necessary beyond what the stairwell CONTAM model can provide. 

One solution, to circumvent this lack of vertical orifice area, is to inject pressurization air at each level of the stairwell. I believe this would greatly minimize the pressure drop effects from a single injection point. How I model that in CONTAM is what I am unclear about. 

Your feedback is greatly appreciated, 

Marko 

[Dols, William Stuart (Fed)]

Marko,

1. The “orifice” to which you are referring is essentially that which describes the resistance to airflow of the shaft itself, stairs, and people using the stairs, e.g., during an evacuation scenario. CONTAM utilizes the cross-sectional area and other properties of the Stairwell model to generate the coefficients of a powerlaw (orifice) model. The airflow path that implements the stairwell airflow element would be defined between each floor of the stairwell.

      

2. Run simulations using 24 m2 and 32 m2 (all else being the same) to see what difference it makes in your results. Meaningful is in the eye of the beholder – very similar results means the stairwell resistance is not as significant a parameter as others might be (e.g., wall and door leakage), whereas very different would mean it is significant and requires greater consideration.
3. This is where you then need to utilize your engineering judgement to come up with a solution. The ASHRAE Handbook of Smoke Control Engineering has an example in Chapter 14 on the use of CONTAM to model stairwell pressurization in an eight-story building.

[Marko Pilic]

Thank you Stuart, 

This clarifies things. 

Another question, how can I determine the pressure drop through the stairwell to know what external static pressure to size the stairwell pressurize fan at? Is it just delta between the Pg values, at the different stairwell floor zones? 

Thank you, 

Marko