[Bldg-sim] Comparing ASHRAE 90.1 App G Models to Real Buildings

[Dru.Crawley at bentley.com]

Impact of weather depends on how climate-responsive the building is.  Recently finished a paper that showed +-5% variation in year-to-year weather in some building types (constant volume systems mostly) and more than 20% in others.  Location and humidity also play a role.  One building type that is extremely energy-intensive (restaurant) also had high variation due to weather - outside preheating/cooling.

Images from extremely hot and extremely cold climates - identical model, actual weather from 1980-2014.  1980 on right. TMY-type files on left.

[cid:image001.png at 01D093B1.C3E98560][cid:image002.png at 01D093B1.C3E98560]

From: Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Jacob Dunn
Sent: Thursday, May 21, 2015 10:05 AM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] Comparing ASHRAE 90.1 App G Models to Real Buildings

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

365 Canal Street Suite 3150
New Orleans LA 70130
504.561.8686
eskewdumezripple.com<http://www.eskewdumezripple.com/>

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