[Bldg-sim] Ot: Re: Modelling simplification for structural concrete columns

[Joe Huang]

It's not an either-or situation, i.e., either use THERM or model the column as a 1-D layer 
with thermal mass.  It's both, use THERM to get a better conductivity, and then use that 
conductivity instead of the nominal  concrete conductivity in the 1-D layer.

Joe

Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 108D
Moraga CA 94556
yjhuang at whiteboxtechnologies.com
www.whiteboxtechnologies.com
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"


On 3/18/2013 1:36 PM, Jeremiah Crossett wrote:
> The thermal mass should also provide a decent benefit-- the reason I did not mention 
> THERM is that it will provide a bridged conductivity- yet will not show the benefit of 
> the mass. It would be nice if THERM could also model the thermal storage potential of 
> the mass. Potentially the thermal storage energy benefits of the mass would be close to 
> the energy loss of the added conductivity from the mass...?
>
> On Mon, Mar 18, 2013 at 12:52 PM, Chris Yates <chris.malcolm.yates at gmail.com 
> <mailto:chris.malcolm.yates at gmail.com>> wrote:
>
>     Hi guys
>
>     Thermal bridges and interstitial condensation can be just as much an issue in hot
>     humid climates as they are in cold. If there's am air leakage path past the pillars
>     then humid exterior air might infiltrate layers.
>
>     A bit off topic, sorry.
>
>     Cheers
>
>     Chris
>
>     Sent from my Android device. Please excuse typos, etc.
>
>     On 18 Mar 2013 03:36, "Patrick Bivona" <patrick.bivona at gmail.com
>     <mailto:patrick.bivona at gmail.com>> wrote:
>
>         Edwin, Graham,
>
>         Thanks for your advice. I had initially misunderstood what Joe was actually
>         proposing to do to take two dimensional conduction into account in and in the
>         vicinity of the columns. I'll follow his and your suggestion. It will be a good
>         learning experience for me anyway.
>
>         To answer your questions about the climate zone, this building is in South
>         Vietnam, so hot and humid all year around with some small variations. The
>         columns won't be insulated and the building will be air-conditioned. A nice
>         thermal bridge but not as bad as in a cold climate. Sadly, this is not the type
>         of project where the energy modelling is informing the design much...
>
>         Regards,
>         Patrick
>
>
>         On 18 March 2013 09:25, Wealend, Edwin <e.wealend at cundall.com
>         <mailto:e.wealend at cundall.com>> wrote:
>
>             Patrick,
>
>             Those are some mighty columns!
>
>             I think it depends on what you’re trying to achieve with the model. If
>             you’re looking at radiant temperatures, local thermal comfort or similar,
>             then I would agree that taking an area weighted approach is going to neglect
>             important local differences due to thermal inertia and other factors.
>             However, if you’re looking at the energy use of the entire building, and
>             it’s conditioned 24 hours, or in a climate with negligible diurnal swing, or
>             with limited thermal mass generally, I would still say that a simplified
>             approach would give you results that are accurate enough. I concur with Joe
>             on the point about thermal bridging. Particularly if the remainder if the
>             façade is insulated. Most construction inputs in energy modelling software
>             don’t accurately account for thermal bridging, so if you think they’re going
>             to be significant, then use a separate 2D calculation software and adjust
>             your u-values appropriately.
>
>             That said, as they’re relatively large and it’s easy enough to divide up the
>             walls into separate constructions, as it is with software like IES, then by
>             all means model them separately and apply a different construction.
>
>
>             Much of the importance of the above is also dependant on the climate your
>             build is in. E.g. Un-insulated concrete columns in a northern European
>             climate are a terrible idea and will come with a big energy penalty. In
>             warmer climates, their contribution to the overall energy of the building
>             will be much smaller and your efforts on the accuracy of their modelling may
>             be better spent looking at something like the fresh air or building leakage.
>
>             Regards,
>
>             Ed
>
>             *Edwin Wealend*
>
>             Senior Engineer
>
>             CUNDALL Hong Kong
>
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>
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>
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>
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> -- 
> **Jeremiah D. Crossett*| Senior Analyst  |  Phase Change Energy Solutions*
> *
> *120 E. Pritchard St.  | Asheboro, NC 27203  | Mobile 503-688-8951*
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