Question-and-Answer Resource for the Building Energy Modeling Community
Get started with the Help page
Ask Your Question

U factor of CMU wall in the components loaded into Openstudio

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

Li_Liu gravatar image

updated 2020-01-20 15:12:37 -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?


edit retag flag offensive close merge delete

1 Answer

Sort by ยป oldest newest most voted

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

jbatt 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.

image description

edit flag offensive delete link more

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

Training Workshops

Question Tools

1 follower


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

Seen: 93 times

Last updated: Dec 03 '18