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

Graham Carter & Megan Lyall hamnmegs at ozemail.com.au
Tue Mar 19 02:31:53 PDT 2013


We just use THERM to work out an effective insulation thickness to account for bridging as well as extended surface area (greater than projected).  We keep the mass the same in the dynamic simulation so you get the effect of both provided you layer the insulation and other layers correctly around the mass …
If insulation is non existent then things get trickier but I am guessing adjusting the conductivity of the concrete to get the same effective U-Value on a projected area basis in THERM won't be too far off depending on what is desired from the simulation ... 
G

On 19/03/2013, at 7:36 AM, 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> 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> 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> 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
> 
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> Jeremiah D. Crossett  | Senior Analyst  |  Phase Change Energy Solutions
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