[Bldg-sim] Ot: Re: Modelling simplification for structural concrete columns
Joe Huang
yjhuang at whiteboxtechnologies.com
Tue Mar 19 09:19:43 PDT 2013
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
>
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>
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> --
> **Jeremiah D. Crossett*| Senior Analyst | Phase Change Energy Solutions*
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