[Bldg-sim] Comparing ASHRAE 90.1 App G Models to Real Buildings (UNCLASSIFIED)
Joe Huang
yjhuang at whiteboxtechnologies.com
Wed May 27 15:09:51 PDT 2015
I don't think the primary cause of discrepancy between simulations and measured data are
the algorithms (although they do play a part), but much more the input assumptions. I
also agree that more calibration should be done, not so much to tune an individual model,
which can easily be taken to a meaningless excess, but more to gain insight into which
input assumptions or defaults are most questionable and need revision of the "conventional
wisdom". A case in point is how much shading from drapes, blinds, and other obstructions
should be assumed? For many years, I've seen and used a SHADING-FRACTION of 0.60, i.e.,
40% of the incident solar is being obstructed, but is that really the best average value ?
(this will likely vary by simulation program).
When this issue of how reliable are simulations was raised at a DOE-sponsored workshop in
Jan. 2012 following the ASHRAE conference in San Antonio, and someone put up the
proverbial plot of simulations vs measured for LEED buildings showing a huge cloud, I had
suggested that we should tackle the calibration process in steps:
1. original ASHRAE-90.1 model vs measured
2. 1 from above corrected to as built and operated (including actual weather!) vs
measured
3. 2 from above with end-use metered data vs measured, plus tuning the model
1 would be what we're doing now. 2 is eminently doable by onsite visit to the actual
building. 3 would require much more instrumentation and manpower, and only doable as a
research project.
What I would like to see is how much do the correlations improve going to 2 and then 3.
My gut feeling is that the standard deviations would be halved each time, i.e., from 40%
to 20% to 10%.
I've actually thought of turning this idea into an ASHRAE WS (RFP), and might still do it,
time and energy permitting. What I envision is for some contractor to get a healthy number
of ASHRAE 90.1 models (~30-40), possibly submitted for LEED, and then apply the same
methodology to get 2, and pick a few (~5) that would be monitored for 3. If there are any
ASHRAE members or friends interested to flush out such a WS, please send me an e-mail.
Joe (currently Chair ASHRAE TC 4.7 on Energy Calculations)
Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 205A
Moraga CA 94556
yjhuang at whiteboxtechnologies.com
http://weather.whiteboxtechnologies.com for simulation-ready weather data
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"
On 5/27/2015 2:34 PM, Justin Spencer wrote:
> Models are never going to agree, but that doesn't mean they aren't powerful tools for
> decision-making. Look at the ASHRAE 140 results for highly simplified geometries with
> different engines. Things easily vary by 20%. Hell, things vary by 20% just between some
> versions of the same tool. I didn't see it mentioned that the underlying models just
> aren't going to give you the "right" answer.
>
> That's why we need to calibrate. The models are not generally actually calculating
> things based on first principles. They use shortcuts for computation time and ease of
> specification everywhere. That's why it's no less real for me to impose some sort of
> somewhat goofy setpoint schedule to get things to work out well in the calibration of my
> model. Ideally, we'd calibrate to one set of bills and then run it against a second set
> of bills to see if we over-calibrated the models (the same as over-fitting a regression
> model). Instead of arguing whether or not the models are right, we should be going back
> to the fundamental question of whether or not the models provide useful decision-making
> information, i.e. whether or not they get the first order impacts right for different
> kinds of design choices in new construction. Remember that uncertainty around each point
> and move ahead making the design decisions you need to make.
>
> There's still plenty of room to develop better analysis practices that will improve the
> design decisions we make. I would love to see a study looking at normalized consumption
> and key characteristics of 5-year-old commercial buildings, and then again at
> 10-year-old commercial buildings. You could do this with LEED submittals and regress
> against the ECMs included and other characteristics. You wouldn't necessarily get to the
> why of how the buildings failed to deliver without a lot of extra work, but I think you
> could get the what just by looking at bills and data. You could also do this on the
> residential side. We have some utility clients who run commercial or residential new
> construction programs. Theoretically, we could get bills and characteristics for a large
> number buildings and regress. I know that would work on the residential side. On the
> commercial side, I don't know if there is enough participant data. Others should
> consider doing the same. It would be a fascinating study and would make for a great
> energy nerd parlor game. Which of these measures just didn't deliver?
>
> My gut says that failures in fancy control systems are to blame for the most egregious
> differences. There are so many failure points -- sensors, valves, dampers, actuators,
> not to mention the likelihood of a mistake in the controls sequence. You need somebody
> on top of monitoring for each of those potential failure points and correcting them. My
> gut also says that good solid basic design will deliver the savings. Cutting down on
> west-facing solar gains will save cooling energy. Installing more efficient HVAC
> equipment, given solid ratings information, will also work. More efficient lighting
> designs will work. Really fancy stuff will fail some of the time. And some of the time
> it will work! And we need to celebrate those pieces that work!
>
> On Wed, May 27, 2015 at 3:02 PM, Fred Betz <fbetz at aeieng.com <mailto:fbetz at aeieng.com>>
> wrote:
>
> Just catching up with this thread so I'm sorry if I'm repeating anything that's
> already been mentioned.
>
> Take a look at the paper from Pam Berkeley et al published last year at SimBuild.
> https://www.ashrae.org/membership--conferences/conferences/ashrae-ibpsa-usa-papers
>
> 10 experienced energy modelers modeling the same building in a 3hr period.
> Fascinating results.
>
>
> There are emerging methods to do more rigorous QC using a variation on Monte Carlo
> for energy models to calculate a confidence interval for the model rather than fully
> rely on modeler experience and 3rd party QC. Georgia Tech has integrated this into
> their version of e+, which I hope gets integrated into a future version of e+. It's
> computationally intense so cloud computing is probably the right way to do this,
> which I believe e+ is heading towards.
>
>
> Fred
>
>
> FRED BETZ PhD., LEED AP ®BD+C
> SENIOR SUSTAINABLE
> DESIGN CONSULTANT
>
> AEI | AFFILIATED ENGINEERS, INC.
> 5802 Research Park Blvd. | Madison, WI 53719
>
> P: 608.236.1175 <tel:608.236.1175> | F: 608.238.2614 <tel:608.238.2614>
> fbetz at aeieng.com <mailto:fbetz at aeieng.com> | www.aeieng.com <http://www.aeieng.com>
>
>
> -----Original Message-----
> From: Eurek, John S NWO [mailto:John.S.Eurek at usace.army.mil
> <mailto:John.S.Eurek at usace.army.mil>]
> Sent: Wednesday, May 27, 2015 11:28 AM
> To: bldg-sim at lists.onebuilding.org <mailto:bldg-sim at lists.onebuilding.org>
> Subject: Re: [Bldg-sim] Comparing ASHRAE 90.1 App G Models to Real Buildings
> (UNCLASSIFIED)
>
> Classification: UNCLASSIFIED
> Caveats: NONE
>
> This is a slightly different question:
> How close do you expect 2 energy models to be created by 2 different modelers (using
> the same program) if you give them the same plans and information?
>
> (Ask Pablo Picasso, Salvador Dali and Rembrandt to draw a tree)
>
> I assume most companies don't double up on the energy modeling efforts which would
> show how consistent or non-consistent energy models are. (assuming the energy
> modelers are experienced and competent.)
>
> Somebody who teachers energy modeling may be able to provide insight and good examples.
>
> As far as an energy model matching the actual utilities bills..... If you have a
> 1000 modelers, making models on 1000 computers for 1000 years......
>
>
>
> -----Original Message-----
> From: Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org
> <mailto:bldg-sim-bounces at lists.onebuilding.org>] On Behalf Of Jacob Dunn
> Sent: Friday, May 22, 2015 2:37 PM
> To: bldg-sim at lists.onebuilding.org <mailto:bldg-sim at lists.onebuilding.org>
> Subject: [EXTERNAL] Re: [Bldg-sim] Comparing ASHRAE 90.1 App G Models to Real Buildings
>
> Thank you all for your thoughtful insight on this matter! It’s an important debate
> – both in understanding the capabilities/limitations of our craft as energy
> modelers, but also to communicate our value to the community at large.
>
>
>
> To clarify slightly, my question revolved around how the specific modeling protocol
> of Appendix G could account for the “performance” gap between modeled and actual
> use. Thus, the fact that buildings aren’t operated as the energy model specified
> and the lack of building commissioning, while true and important, are not inherent
> to the intent of Appendix G modeling. The most interesting question is, “If you
> model a LEED App G model perfectly according to protocol, AND the building was
> operated according to the modeled schedules, will it predict the right number?”
> Lots of your responses lent insight into this question, thanks again!
>
>
>
> I’ve revised my list below based on your responses:
>
>
>
> Added:
>
> - Plug load values are assumed, which can have a huge impact on overall energy
> (Thanks Christoph and Chris Hadlock for the insight)
>
> - Insulation values are largely specified without thought to thermal bridging
>
> - HVAC controls simulation is often simplified
>
> - Performance curves are often not simulated due to increased effort and
> unavailability of performance data from manufacturers
>
>
>
> Original:
>
> - 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
>
> Cheers,
>
>
>
> 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 <tel:504.561.8686>
>
> eskewdumezripple.com <http://eskewdumezripple.com> <http://www.eskewdumezripple.com/>
>
>
>
> From: Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org
> <mailto:bldg-sim-bounces at lists.onebuilding.org>] On Behalf Of Chris Hadlock
> Sent: Friday, May 22, 2015 1:08 PM
> To: Christoph Reinhart
> Cc: bldg-sim at lists.onebuilding.org <mailto:bldg-sim at lists.onebuilding.org>
> Subject: Re: [Bldg-sim] Comparing ASHRAE 90.1 App G Models to Real Buildings
>
>
>
> 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
> <mailto: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
> <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 <tel:617%20253%207714> , f: 617 253 6152
> <tel:617%20253%206152> , creinhart at mit.edu <mailto:creinhart at mit.edu>
> <mailto:creinhart at mit.edu <mailto: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
> <http://architecture.mit.edu/event/modeling-urban-sustainability-energy-daylight-and-walkability>
> | DIVA Day 2015 <http://diva4rhino.com/diva-day-2015>
>
>
>
>
>
>
>
> From: Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org
> <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 <mailto: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 <tel:%2B1.443.718.4881> <tel:%2B1.443.718.4881> direct |
> Alamelu.Brooks at icfi.com <mailto:Alamelu.Brooks at icfi.com>
> <mailto:Alamelu.Brooks at icfi.com <mailto:Alamelu.Brooks at icfi.com>> | icfi.com
> <http://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
> <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 <mailto: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
> <mailto: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 <tel:763.276.9981>
>
> M:
>
> 415.420.9314 <tel:415.420.9314>
>
> http://www.iesve.com <http://www.iesve.com/>
>
> Integrated Environmental Solutions Limited. Registered in Scotland No. SC151456
> Registered Office - Helix Building, West Of Scotland Science Park, Glasgow G20 0SP
>
> Email Disclaimer <http://www.iesve.com/disclaimer.html>
>
>
>
>
>
> From: Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org
> <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 <mailto: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
> <mailto: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 <tel:504.561.8686>
>
> eskewdumezripple.com <http://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 <tel:616.450.8653>
> jim at buildingperformanceteam.com <mailto: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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>
> Classification: UNCLASSIFIED
> Caveats: NONE
>
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