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EnergyPlus airflow network error

asked 2024-06-04 23:11:23 -0500

Bill's avatar

updated 2024-06-06 08:48:53 -0500

Hi all, I am trying to do some modelling for the natural ventilation using EnergyPlus airflow network, but I am stuck in the airflow network: Multizone; component; detailed opening. The windows are all the same, awnings (top hinged). The maximum openness of windows is 45 degrees. I need help to understand 'the height, width, and start height factor for opening factor 1, and factor 2. I tried many options, but I had severe errors in assigning windows to each surface. The inputs I used are Opening-factor 0, Discharge-coefficient-for-opening-factor-1 0.001, width-factor-for-opening-factor-1 0, height-factor-for-opening-factor-1 0, and start-height-factor-for-opening-factor-1 0. opening-factor-2 1, discharge-coefficient-for-opening-factor-2 0.5, width-factor-for-opening-factor-2 0.50, height-factor-for-opening-factor-2 0.5, and start-factor-for-opening-factor 2 0. Thanks for your help in advance.

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answered 2024-06-06 21:35:13 -0500

Jamie Sullivan's avatar

updated 2024-06-06 21:36:55 -0500

So, this can get kind of messy and complicated depending on how you build your model.

The basics are that each of the discharge coefficient, width factor, and height factor settings controls how those parameters will scale according to the window opening factor. So, for example, if you have the width factor set to equal 0 when the opening factor is 0, and 1 when the opening factor is 1, then when the opening factor is 0.5 the window width factor will also be 0.5.

It is the product of the discharge coefficient, width factor, and height factor that defines the actual effective window opening area. This can result in some interesting scaling if you allow all three of them to vary at once. In your example you have the discharge coefficient varying from 0.001 to 0.5, and the height and width factors both varying from 0 to 0.5. This means that the maximum opening area of the window will be equal to 0.5x0.5 = 25% of the window area, with a coefficient of 0.5. If your opening factor is only 0.5, then the effective opening area will not be half the maximum - instead it will be 0.5 x 0.5 x 0.5 = 12.5% of maximum effective area (i.e. 12.5% of 25% of the window area).

If you want the window area to scale in a more intuitive linear fashion, it may be better to fix both the discharge coefficient and the width factor and only vary the height. That way, when the window is 50% open the effective opening area will also be 50% of the maximum.

Below, for example, is a typical window definition in one of my models using this approach. Here I have set the maximum height factor (i.e. the height when the opening factor = 1) to 0.2 / 20%. This was estimated by using this window opening calculator from the UK. I have the air moss flow coefficient when opening is closed input set very low because I didn't want to be modelling the infiltration using the AFN in this case.

AirflowNetwork:MultiZone:Component:DetailedOpening,
ExteriorWindowAwning_0.2,    !- Name
0.0000001,               !- Air Mass Flow Coefficient When Opening is Closed {kg/s-m}
0.65,                    !- Air Mass Flow Exponent When Opening is Closed {dimensionless}
NonPivoted,              !- Type of Rectangular Large Vertical Opening (LVO)
0,                       !- Extra Crack Length or Height of Pivoting Axis {m}
2,                       !- Number of Sets of Opening Factor Data
0,                       !- Opening Factor 1 {dimensionless}
0.62,                   !- Discharge Coefficient for Opening Factor 1 {dimensionless}
1,                       !- Width Factor for Opening Factor 1 {dimensionless}
0,                       !- Height Factor for Opening Factor 1 {dimensionless}
0,                       !- Start Height Factor for Opening Factor 1 {dimensionless}
1,                       !- Opening Factor 2 {dimensionless}
0.62,                    !- Discharge Coefficient for Opening Factor 2 {dimensionless}
1,                       !- Width Factor for Opening Factor 2 {dimensionless}
0.2,                       !- Height Factor for Opening Factor 2 {dimensionless}
0;                       !- Start Height Factor for Opening Factor 2 {dimensionless}

Note however that letting ... (more)

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That is the clearest explanation about how these coefficients interact. Many thanks.

Bill's avatar Bill  ( 2024-06-07 20:36:18 -0500 )edit
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answered 2024-06-05 09:48:53 -0500

pmarclay's avatar

Hi Bill

You might want to try the follwing settings: The height factor refers to the width of the window or opening. You must check whether the defined opening is opened over its entire width or whether the openable part deviates from this. With this window shape, the width factor refers to how strongly the window is pushed upwards (45° in your case). This means that if your window is opened over the entire opening width, you select 1 as the height factor. To then determine the width factor, you must use triangulation to calculate how large the free area is through which the air can flow in and out through the window. With a 45° opening, not the entire cross-section of the whole window is available. If you then know what percentage of the total free opening your 45° opening is, you can derive the with-factor from this. This can mean, for example, that the height-factor is 1 and the with-factor is 0.3 (or more), which must be determined individually. At the same time, set the discharge-coefficient for opening-2 to 1 and the start height-factor for opening-2 to 0 (i.e. the window is pushed upwards from below).

I hope this can help you.

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Thank you for that helpful explanation

Bill's avatar Bill  ( 2024-06-07 20:35:35 -0500 )edit

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Asked: 2024-06-04 23:11:23 -0500

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Last updated: Jun 06