[Bldg-sim] Comparing ASHRAE 90.1 App G Models to Real Buildings
Dru.Crawley at bentley.com
Dru.Crawley at bentley.com
Thu May 21 07:34:52 PDT 2015
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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