[Bldg-sim] Modelling simplification for structural concrete columns

[Patrick Bivona]

Thank you all for your feedback!


On 13 March 2013 19:49, Hall, Brendan <BHall at karpinskieng.com> wrote:

>  To the original post, I would use the line of the wall and ignore the
> columns. If you feel that there is a considerable shading effect, then use
> side fins or a building shade. Look at a section of wall the width of one
> column spacing as calculated the combined U value and thermal mass of the
> wall to see if the columns will have enough of an effect to make it worth
> modeling. I don’t know how large the columns you are referring to are but
> it is likely that they would have a negligible effect on the model as a
> whole, especially when you consider the uncertainty of other values that
> are input. There is a line in Table G3.1.5 saying that other envelope
> assemblies that cover less than 5% of the total area need not be explicitly
> model and can be averaged into other wall assemblies.****
>
> ** **
>
> As to Jeremiah’s post, ****
>
> ** **
>
>    - ASHRAE 90.1 does not require thermal bridging to be modeled in the
>    baseline.****
>
> Thermal bridging should also be taken into account when calculating wall
> and floor U Values. External un-insulated assemblies must be explicitly
> modeled.****
>
>    - ASHRAE 90.1 does not require internal mass to be modeled in the
>    baseline.****
>
> I don’t think any internal constructions are addressed in 90.1. Generally
> the effect of any internal walls will be negligible compared to the
> external walls unless your typical wall is heavy weight like a concrete
> block wall. Some schools are like this. Either way I would say internal
> mass would not need to be included in the baseline since the baseline is a
> metal framed building, which implies GWB internal walls.****
>
>    - 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.**
>    **
>
> The baseline should used a metal framed wall, which still has some mass
> effects that are required to be modeled. The way I understand it, a “light
> weight” wall refers to neglecting the mass effects of walls in your
> calculations.****
>
> ** **
>
> ** **
>
> Brendan Hall****
>
> ** **
>
> *From:* bldg-sim-bounces at lists.onebuilding.org [mailto:
> bldg-sim-bounces at lists.onebuilding.org] *On Behalf Of *Jeremiah Crossett
> *Sent:* Wednesday, March 13, 2013 12:36 AM
> *To:* Patrick Bivona
> *Cc:* bldg-sim at lists.onebuilding.org
> *Subject:* Re: [Bldg-sim] Modelling simplification for structural
> concrete columns****
>
> ** **
>
> 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 *
>
>   [image: Image removed by sender.]****
>
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