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

Fri May 22 11:07:32 PDT 2015

All,

I would agree with all of the factors mentioned that absolutely can result
in deviations between actual and modeled building performance. I would also
echo the sentiment that following modeling rules shouldn't necessarily
preclude us from attempting to better predict actual building performance
through the LEED process. Applying careful attention to important details
and a healthy dose of experience (bringing together real life building
performance knowledge as it relates to the grey areas - namely schedules,
equipment controls, occupant behavior, etc) can truly help close the gap.
At the end of the day, a rating system should be attempting to reward
buildings that actually perform well, not theoretically perform well (and
as modeler's we should take a leading role in making *good* (i.e.
fair) assumptions).

My colleague (Janine Vanry) has recently completed research (to be
published soon) for her masters thesis at the University of Waterloo
(Ontario, Canada) which studied how LEED certified academic buildings in
southwestern Ontario performed in comparison to government energy intensity
benchmarks, campus-wide energy intensities, and in general how LEED
(modeled) results compare to actual building performance (as measured
through M&V). Consistent with Dr Samuelson's (et al.) research findings, the
discrepancies between the modeled results and the actual energy intensities
showed that there was an under-prediction anywhere from 2% to 44%.

While energy modeling professionals understand (as is evident by this
thread) that there will be differences between the documented EAc1 energy
savings and actual building energy usage, this isn't always communicated
and understood by the building owners and the professionals we work with.

Chris

On Thu, May 21, 2015 at 10:56 AM, Christoph Reinhart <tito_ at mit.edu> wrote:

>  Dear Jacob,
>
>
>
> This is an eternal debate and there are many reasons for moving away from
> the use of 90.1 Appendix G to evaluate the performance of a building
> designs.  To answer your question directly, we worked a few years ago with
> Enermodal in Canada on a comparison between design phase building energy
> models (BEM) prepared for LEED Canada certification (slightly different to
> Appendix G) to calibrated BEM and measured energy use for 18 buildings. The
> main findings are quoted below:
>
>
>
> *Analysis of a Simplified Calibration Procedure for 18 Design-Phase
> Building Energy Models*
>
> H W Samuelson, A Ghorayshi and C F Reinhart
>
> Journal of Building Performance Simulation, DOI:
> http://dx.doi.org/10.1080/19401493.2014.988752
>
> This paper evaluates the accuracy of 18 design-phase building energy
> models, built according to LEED Canada protocol, and investigates the
> effectiveness of model calibration steps to improve simulation predictions
> with respect to measured energy data. These calibration steps, applied in
> professional practice, included inputting actual weather data, adding
> unregulated loads, revising plug loads (often with submetered data), and
> other simple updates. In sum, the design-phase energy models underpredicted
> the total measured energy consumption by 36%. Following the calibration
> steps, this error was reduced to a net 7% underprediction. For the monthly
> energy use intensity (EUI), the coefficient of variation of the root mean
> square error improved from 45% to 24%. Revising plug loads made the largest
> impact in these cases. This step increased the EUI by 15% median (32% mean)
> in the models. This impact far exceeded that of calibrating the weather
> data, even in a sensitivity test using extreme weather years.
>
>
>
> Best,
>
>
>
> Christoph
>
> Christoph Reinhart
>
> Associate Professor
>
> Department of Architecture
>
> Massachusetts Institute of Technology
>
> 77 Massachusetts Ave, Rm 5-418, Cambridge, MA 02139, USA
>
> t: 617 253 7714, f: 617 253 6152, creinhart at mit.edu
>
> Sustainable Design Lab <http://mit.edu/SustainableDesignLab/> | DIVA
> <http://www.diva4rhino.com/> | Daysim <http://daysim.ning.com/> | mapdwell
> <http://www.mapdwell.com/> | umi <http://www.urbanmodeling.net/>
>
> -------------------------------------------------------------------------
>
> Events  Modeling Urban Sustainability
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> | DIVA Day 2015 <http://diva4rhino.com/diva-day-2015>
>
>
>
>
>
>
>
> *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
> <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*
>
> O:
>
>   763.276.9981
>
> M:
>
>   415.420.9314
>
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>
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> Email Disclaimer <http://www.iesve.com/disclaimer.html>
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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
>
> *eskewdumezripple.com <http://www.eskewdumezripple.com/>*
>
>
>
>
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>
> --
>
> James V Dirkes II, PE, BEMP, LEED AP
> CEO/President
> The Building Performance Team Inc.
> 1631 Acacia Dr, GR, Mi 49504
>
> Direct: 616.450.8653
> jim at buildingperformanceteam.com
>
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>
> The truth is still the truth, even if nobody believes it.  A lie is still
> a lie, even if *everyone* believes it.
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