Bldg-Sim Community -

I'm trying to compile a list of why it might be inappropriate to compare Appendix G models to actual consumption data. This comes about because I recently got into a debate with one of my co-workers when looking at the infamous NBI chart/study that shows little correlation to predicted and actual energy values of LEED buildings. I was trying to explain that the Appendix G model's intent is NOT to be compared to actual consumption, as it is a modeling protocol aimed at creating consistent relative comparisons for LEED points.

Here are the reasons thus far that support this notion (that App G models shouldn't be compared to actual data). Does anyone know of any resources out there that expand upon this? Or can you think other reasons?

- Appendix G does not take into account external shading, which can be critical in urban environments for accurate energy predictions

- Schedules are typically not created with the intent of being predictive. Overall building hours are adhered to, but detailed schedule creation is not usually in the scope of a LEED model (or is it, in your experience?). For instance, typical plug load base values during unoccupied times are .3, this is a pretty big assumption.

- The App G model uses a TMY weather file, which can vary from the current weather year (I wonder on average by how much?)

- Infiltration values are assumed, unless blower door testing has been done (which is rare for commercial buildings).

- Thermostat values are modeled as consistent across the building, which is rarely the case in an actual operating building

Any additional insight is much appreciated!

Jacob Dunn LEED AP BD+C

ESKEW+DUMEZ+RIPPLE, APC
2014 AIA National Architecture Firm Award

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