[Bldg-sim] Modelling simplification for structural concrete columns

Jeremiah Crossett jcrossett at phasechange.com
Tue Mar 12 21:36:15 PDT 2013


Group,
Please do correct me if I am wrong--->>

   - ASHRAE 90.1 does not require thermal bridging to be modeled in the
   baseline.
   - ASHRAE 90.1 does not require internal mass to be modeled in the
   baseline.
   - ASHRAE 90.1 does not require self shading to be modeled in the
   baseline.
   - ASHRAE 90.1 requires a light weight wall assembly for the baseline.

So the conclusion is that this does not need to be modeled in the baseline
and the question becomes how to model this in the proposed building, or
actually "what gets the project more LEED credits" If I where to do it I
would: (in E+)

   - Ignore the shading element of the concrete pillars and consider the
   walls that separate the zones the only thing that matters for shading.
   - Dependant on the other wall construction-- if mass than add the
   thickness to the total wall area-- if steal framed, wood&other or metal
   than bridge wall with column and add internal mass to account for thermal
   mass.

My conclusion is your #1 should be fine, especially if your not attempting
to get credit for the exposed thermal mass..

On Tue, Mar 12, 2013 at 8:36 PM, Patrick Bivona <patrick.bivona at gmail.com>wrote:

> 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
>
>
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-- 
*Jeremiah D. Crossett  | Senior Analyst  |  Phase Change Energy Solutions*
*
120 E. Pritchard St.  | Asheboro, NC 27203  | Mobile 503-688-8951
www.phasechange.com
*
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