Airflow path- Element

[Giannis Papadopoulos]

Hello everyone,

I have start to use contam and  I have some problems with the airflow Element types, as i don't know which is the best type  to use. First of all, I simulate an office buildings  and i want to validate the co2 concentrations that i measured with the co2 concentrations of CONTAM. Which element do you prefer for a close window? FIrstly, I choose to use Leakage element and use the values of ASHRAE Handbook of Fundamentals and more the specifically the  values of table ''effective air leakage areas (low-rise residential applications). I choose to use the double horizontal slider, not weather-stripped, which the most closed element with the real windows of the office building that I simulated,  with the value of 1.1 cm2/m. The results of CO2 concentrations are very high and much higher of the measured ones. Then i choose to used the powerlaw model. So i take values for the numerical Data for Air Infiltration & Natural Ventialtion Calculation from AIVC. I take for closed windows C=0.061 with n=0.6, but i cannot understand how this element takes into account the number of the windows and the total length of them. The results using this element seems to better, but i still to have the previous questions.

So summarizing which element do you use for close windows and for open? Also for walls i will appreciate if you tell me which element do you used for the walls too.

Thank you,

Best regards,

Giannis

[William Dols]

Giannis,

Please refer to the video tutorials and accompanying files available via the NIST Multizone Modeling website.

https://www.nist.gov/el/energy-and-environment-division-73200/nist-multizone-modeling/contam-video-tutorials
They provide some fairly detailed methods to define building airflow elements based on building pressurization/blower door measurement data.
If you do not have such data, then you will need to utilize some engineering judgement to specify building leakage which can vary widely from building to building.
- Stuart

[Giannis Papadopoulos]

Thank you, but i still not understand how the powerlaw model take into account the characterictics of the window (total area of it). Also, apart from ΑΣΗΡΑΕ there is another source that i can find values of leakage elements?

Thank you,

Giannis

[Dols, William Stuart (Fed)]

Giannis,

Where to begin?

Refer to Chapter 16 of the ASHRAE Handbook of Fundamentals 2022 and the Airflow Theory section of the CONTAM User Guide for the following.
CONTAM provides multiple forms of the powerlaw airflow element.
In its most basic form:

As in the example files provided, one can assume a Normalized Leakage for a residential building or perform a blower door test to measure mass flow, in kg/s (or in m³/s), at various values of to obtain C and n.
One can also assume the powerlaw form of an orifice.
In this form of the powerlaw equation, the orifice Area is available.
One can then obtain an effective leakage area for the orifice from the conversions offered in the HoF.

If one assumes a total leakage area for a building and normalizes it by the total building surface area, then one has a leakage per building surfaca area, e.g., cm²/m².
This is similar to what was done in the tutorial.

One could also measure the leakge of individual building components, e.g., windows.
This could be normalized by window area or window perimeter (assuming similar construction of windows of various dimensions).
CONTAM allows one to utilize any form, leakage area per item, leakage area per length, or leakage are per area.
For a window, one would then assume one of these “normalized” forms to define a window leakage element.
Then each flow path that references this element would be provided a multiplier to obtain the total leakage for the specific flow path.
Therefore, the multiplier would either be total windows, total window perimeter length, or total window area.
This is for closed windows.

For open windows, one would use the Large Opening element types.

Again, engineering judgement is required to decide how to aportion leakage within a building model.
This judgement includes knowledge of the emperical data avaialbel to the modeler.

For what it’s worth, there are also libraries of input data available on the NIST Multizone Modeling website.
However, you will notice that there is no longer a table of leakge data available in the HoF.
This is due the fact that buildin leakage varies so widely, and there are few correlations that relate leakage to building properties.

- Stuart