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U factor of CMU wall in the components loaded into Openstudio

asked 2018-11-24 18:02:49 -0600

Li_Liu gravatar image

updated 2018-11-25 10:22:00 -0600

When I loaded a component "Concrete Block - 8 in. - 105 lb/ft3 - Solid Grouted" from the BCL online, and then run the model, I can see that the U factor with film is 3.15 W/m2K, which is 0.5547 Btu/ft2hR. But per the TEK note 06-02C1 from NCMA, it should be 0.527 Btu/ft2hR. What makes the difference?

Thanks!

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answered 2018-12-03 16:29:34 -0600

jmbattis gravatar image

updated 2018-12-03 16:30:52 -0600

When I look at the material inputs for Concrete Block - 8 in. - 105 lb/ft3 - Solid Grouted and use these (along with the ASHRAE-defined values for film coefficient) I get:

1/(0.17 + (8/8.4) + 0.68) = 0.5548 Btu/ft2-h-R

So the OpenStudio/EnergyPlus output makes sense to me. The difference could lie in a slight discrepancy in thermal conductivity value or (more likely) the fact that film coefficients are approximations that are subject to vary depending on what standard you are referencing or what software you are using. If you wanted to match the value that you found, I would advise adjusting the input for thermal conductivity since it seems like OpenStudio's assumed film coefficients are consistent with ASHRAE.

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Asked: 2018-11-24 18:02:49 -0600

Seen: 30 times

Last updated: Dec 03