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

Thu May 21 07:55:12 PDT 2015

There is a section in Appendix G (G1.2) addressing this:

Neither the proposed building performance nor the

baseline building performance are predictions of

actual energy consumption or costs for the proposed

design after construction. Actual experience will differ

from these calculations due to variations such as occupancy,

building operation and maintenance, weather,

energy use not covered by this procedure, changes in

energy rates between design of the building and occupancy,

and the precision of the calculation tool.

You may also want to check out articles on building labeling systems that discuss differences between asset (theoretical, modeling-based) and operational (based on actual utility bills) ratings, such as the one attached (see p.4-6). Both have value as long as they are interpreted correctly.  

Maria

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From: Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Brooks, Alamelu
Sent: Thursday, May 21, 2015 10:43 AM
To: Jim Dirkes; Nathan Kegel
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Comparing ASHRAE 90.1 App G Models to Real Buildings

I believe Appendix G is not meant to measure the performance of the existing building. ASHRAE 90.1 Appendix G Technical Committee is the right source to answer this question. They can clarify the intention of the APP G modeling methodology.

Best,

Alamelu

Alamelu  Brooks LEED AP (BD+C), HBDP, BEAP, EIT| Senior Associate | +1.443.718.4881 direct | Alamelu.Brooks at icfi.com | icfi.com 

ICF INTERNATIONAL | 7125 Thomas Edison Drive, Suite 100, Columbia, MD 21046 USA 

Connect with us on social media <http://www.icfi.com/social> .

From: Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Jim Dirkes
Sent: Thursday, May 21, 2015 10:36 AM
To: Nathan Kegel
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Comparing ASHRAE 90.1 App G Models to Real Buildings

I agree fully with all of the above comments and would like to add these:

*	Even buildings that are commissioned properly will see their performance erode over time.  There are hundreds of reason for this, ranging from poor maintenance to well-intentioned maintenance people not having time to monitor operations well.  There is NO BUILDING that operates well for long.
*	Buildings often see changes in operation, occupancy and schedule.  These are oftimes gradual changes over a period of years, but can be substantial

On Thu, May 21, 2015 at 10:22 AM, Nathan Kegel <nathan.kegel at iesve.com> wrote:

Climate files used in the simulations versus the actual weather.

I’m in the midst of a project that shows a variance in EUI of up to 200% just by changing the climate file for the DOE primary school.  Full results to be presented in September.

Add in all the other factors already mentioned, and if your 90.1 model comes anywhere close the real buildings’ it’s far more likely that the 90.1 model was extremely “lucky” than it is that the model used accurate assumptions.

Regards,

Nathan

 <http://www.iesve.com/> 

Nathan Kegel
Business Development Manager

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From: Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Maria-Lida Kou
Sent: Thursday, May 21, 2015 9:17 AM
To: Jacob Dunn
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Comparing ASHRAE 90.1 App G Models to Real Buildings

Jacob,

Happy to hear that other people are thinking the same. 

I was into this subject on my own thoughts recently.

I would like to add in your list: Occupants' behavior actually which is not in the stage to be included into the prediction.

I would add commissioning as well along with controls simulation and controls operation.

Apologies because I haven't worked with LEED projects but I think the above applied in general to "the performance gap".

Really looking forward to hearing more about this subject as I am not that experienced engineer yet, but really interested in "the performance" side of buildings.

Best,

Maria-Lida Kounadi

2015-05-21 15:04 GMT+01:00 Jacob Dunn <jdunn at eskewdumezripple.com>:

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

 <http://www.eskewdumezripple.com/> eskewdumezripple.com

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