[Bldg-sim] Modelling simplification for structural concrete columns

[Wealend, Edwin]

Patrick,

I wouldn't worry about the construction thickness, this has little bearing on the overall energy consumption. Any energy model is an estimation of the actual geometry and if it's out by 1% on floor area it's not going to be significant overall. Ensure any shading effects on windows are picked up (Some software allows you to do this with a shading device object, others might need it specified in the window setup) and that the overall area weighted U-value for your wall, including the concrete column areas is correct. Ensure your baseline is modelled in a consistent way and the LEED reviewers won't have anything to question. It's when you try to gain unfair advantage that they will have an issue.

Hope that helps.

Edwin Wealend
Senior Engineer

CUNDALL Hong Kong
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Wanchai, Hong Kong
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From: Patrick Bivona [mailto:patrick.bivona at gmail.com]
Sent: Wednesday, March 13, 2013 11:36
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] Modelling simplification for structural concrete columns

Hi everyone,

I'm wondering how best to simplify a model when considering structural concrete columns.
My modelling is in the context of the LEED whole building energy modelling. So I'm concerned with accuracy as much as acceptability by the LEED reviewers. I've read the ASHRAE 90.1 user's manual but didn't find a satisfactory answer.
Here's an example:

        ----
wall   |    | wall
-------|    |------
       |    |
        ----
   concrete column

I can see 3 options for simplifying, each with its own issues:

1. Make the external surface of the column at the same level of the surrounding walls and model the column surface as having its true thickness . The issue is that it alters the area of the space inside and doesn't account for the shading effect of the column.

2. Follow the internal boundary of the column, which introduces 3 surfaces. Not sure what construction thickness to assign to these surfaces. This preserves the internal space area but alters the shading effect of the column.

3. Follow the external boundary of the column. This also introduces 3 surfaces. Not sure what construction thickness to assign to these surfaces either. It preserves the shading effect of the column but alters the area of the internal space.

I'm leaning towards option 1. What do you think? Are they other better options I overlooked?

Of course, things get a bit more complicated when the walls either side are not aligned or in the same plan...

Thanks!
Patrick
For further information about Cundall please visit http://www.cundall.com/Locations/Asia/Asia.aspx
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