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

[Wealend, Edwin]

Chris,

I totally agree. Thermal bridging is an issue everywhere. My point was that in an energy model, the contribution of a thermal bridge to the overall energy mix of the building in hot climate will be much lower. You have to trust your facade consultant or architect has done his job!

Regards,
Ed

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><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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