UA calculation failure in test_bldg_13

[weilixu]

In PR #1823, test_prm_baseline_bldg13 failed in the CI test. Debugging reviewed that the failure is caused by Surface 1624 and Surface 1666, 2 RoofCeilings in plenum space, have construction assigned as Ffactor Ground Floor 4_005, a Construction:FfactorGroundFloor object.

Due to the assignment of FfactorGroundFloor construction, the uFactor cannot be calculated and the test failed this specific line.

Digging deeper in the test model file: bldg_13.osm, both Surface 1624 and Surface 1666 have no Construction assigned, and they both adjacent to a surface that has construction of Ffactor Ground Floor 4_005. It seems in this case, OpenStudio assigns the adjacent surface's construction as default for these two surfaces - and this causes the error in the failed line mentioned above.

I want to understand the intent of having a roof ceiling adjacent to a floor in this test case, since it was never a problem until now, especially the changes in PR #1823 has nothing to do with what we found here. - should I update the code to accommodate this behavior or modify the test file?

[mdahlhausen]

This seems like an issue in the base model and something we should catch in that method. Working on a fix. Thanks for making an issue!

[mdahlhausen]

Thoughts:

• I'm not able to recreate the error running the test on windows or linux with OS 3.7 or 3.8.
• This error appears in the surface_subsurface_ua() method. The surface_subsurface_ua() method is used only in space_conditioning_category(). surface_subsurface_ua() can probably be replaced, or refactored and moved to the Constructions module.
• As you described, the error is caused by a surface adopting the construction of the adjacent surface, an FfactorGroundFloor construction, which does not have a U factor.
• The model is malformed - to surfaces are adjacent, but one is assigned an FfactorGroundFloor construction. That ought to not be a valid construction for surfaces with another surface as the boundary condition.

Fixes:

• Delete the FfactorGroundFloor construction assignment for the two adjacent surfaces; that construction was only used on those two surfaces. Have the adjacent surfaces use the default construction.
• Add a check to make sure the optional U factor is initialized.