Thermal Mass Wall and R-Value

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When creating a model, i noticed that the R-value of the concrete i am using
is the "effective" R-value, rated at 22. Should i use this or should i ask
the concrete manufacturer for a steady-state R-value which will be much more
accurate based on the materials?

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Rob Hudson

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That doesn't sound right. Poured concrete has an R-value around
0.08/inch. When "effective" is used commercially it normally is a hocus
pocus addition for the mass effect but shouldn't be much more than 10%.
eQuest would calculate it as a lag effect based on the mass, so a steady
state value would be most appropriate.
Bruce Easterbrook

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That is the answer i was expecting to here. thanks for your input

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The best thing to do is model the actual wall construction, not just an
equivalent R-value, then you will get both the thermal resistive and the
mass effect properties in the model.

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Karen

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I agree with Karen. I have another thought though: could this be an
insulating concrete form wall (ICF) wall? Google ICF for info.

Carol

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At least one of the ICF companies is using "effective" R-values for
their products. I attended a Home Show recently and was told R-50 for a
concrete wall with only four inches of foam board:
http://www.arxx.net/ICF_INSULATED_CONCRETEFORMS_r50.htm

They claim benefits of thermal mass and reduced infiltration to justify
the value.

As Karen said, best to model the actual wall construction layers.

Regards,

William Bishop, EIT, BEMP, LEED(r) AP

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