[EnergyPlus_Support] C-Factor for Underground Walls and F-Factor for Slab-on-Ground Floors (ASHRAE 90.1, Title 24 etc)

[<seanking.1970@xxxxxxxxxxx>]

Hi, 

I have questions on setting C-Factor of Underground Walls and F-Factor for Slab-on-Grade Floors in EnergyPlus while doing an ASHRAE 90.1/LEED modeling. 

As shown in ASHRAE Standard 90.1 Tables 5.5-1 through 5.5-8, C-Factor and F-Factor values are presented for below grade walls (underground walls in other words) and slab-on-grade floors respectively, E+ has two objects dealing with these constructions - CFactorUndergroundWall and FfactorGroundFloor, which only require C-Factor and F-Factor values and some geometrical readings (height, perimeter, area, etc), with "Outside Boundary Condition" for these surfaces being set to "GroundFCfactorMethod". This seems very simple and straightforward. And my best understanding on this mechanism is E+ will convert these input into equivalent layered settings behind the scene and then do the calculation (detailed in InputOutputReference document V8.1 pdf page 202).

However, I notice that ASHRAE Standard 90.1 2007 Appendix A statements on page 91, section A4.1 and also page 95, section A6.1 "For the purpose of Section A1.2. the base assembly is ......". Does this only apply to "Applicant-Determined Assembly C-Factors, F-Factors" as stated in A1.2? Also, if we do need to set applicant determined C-Factor, the only figure we need to get from Table A3.1B or A3.1C is "C-Factor", in other words, in E+ we still do not need to use layered construction for this below grade wall. Is it right?

One more question, for basement ground floor (ground floor for an underground zone), F-Factor is not applicable because there is not any exposed perimeter (value is zero) can be assigned. Instead, we should use normally underground floor layered setting (with a U-factor) and "Outside Boundary Condition" should be set to "Ground". Is this also right please? And does above apply to an underground wall without connection to grade level (for example, underground wall from a second level basement zone)?

I appreciate very much any advice/comment.

Best regards,

Sean

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