Ot: Re: Modelling simplification for structural concrete columns

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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

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Chris Yates2's picture
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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...?

Jeremiah Crossett2's picture
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Thermal bridges are rarely the same in hot-humid as they are in the cold. ?The difference in temperature between the design temperature and the thermostat set-temperature is significantly smaller so there is much less conduction. ?So, in a lot of instances it can be disregarded.
?
Paul Hay MBA, BA(Arch)

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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

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.
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

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 fa?ade 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,

Edwin Wealend

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Cheers Ed

I agree that the columns are unlikely to have a significant impact on the
energy model - even if they're quite big.

Bye for now

Chris

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Chris Yates2's picture
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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

hamnmegs at ozemail.com.au's picture
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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 Huang

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