[Bldg-sim] Comparing ASHRAE 90.1 App G Models to Real Buildings
Jim Dirkes
jim at buildingperformanceteam.com
Thu May 21 10:50:39 PDT 2015
It occurs to me that every energy modeler "worth his / her salt" recognizes
the limitations of a "baseline" model. It's a reference point intended to
compare with another reference. It's a relative, not an absolute,
comparison.
The models which compare predicted versus actual (e.g., utility bill)
performance are a different matter. At that point, you start trying to
gain understanding about why the model differs from reality. Until you
have actual data, however, it's all relative and may bear little
resemblance to reality.
On Thu, May 21, 2015 at 1:44 PM, Nicholas Caton <ncaton at catonenergy.com>
wrote:
> Lots of strong points raised so far – I think this “conversation/debate”
> is one we must have all faced at some point.
>
>
>
> I don’t have much else to add to what’s already been suggested, except to
> note many of the critical assumptions of occupant behavior / plug load
> density / system operations have an additional layer of obfuscation that
> shouldn’t be missed for new construction calibration: NC buildings’ actual
> energy bills immediately after occupancy are usually NOT representative of
> “typical” usage (for which Appendix G models are necessarily/justifiably
> based upon). The occupants are settling into, learning to operate, and
> calibrating/messing with/breaking the building’s systems. System
> commissioning is working the bugs out of actual system operations to match
> (or improve upon) the original design. I’ve also run into it taking some
> years to wrestle with the local utility when the wrong rates are applied to
> the building. Whenever I am tasked with calibrating from a newly occupied
> building (LEED/App.G or otherwise), it’s a high priority to determine at
> what extent the available utility metering/bills may be skewed by such
> “growing pains.”
>
>
>
> With all this said however, all these “shortcomings” for mis-applying 90.1
> Appendix G models to the task of “predicting” actual energy costs help to
> frame what they are actually very GOOD for. I think it might behoove you
> to at least outline that purpose in contrast:
>
> - [*insert G1.2 here*]
>
> - Correctly developed 90.1 App. G models make very decent
> “platforms” from which to develop a calibrated model down the road.
>
> o They have the advantage of a structured set of assumptions which can
> be transformed into a checklist for surveying actual operations.
>
> o For developing a calibrated model “from scratch,” much of the first
> stages of development are ready-made with a Proposed Appendix G model.
> Geometries, construction/window types, LPD’s, and mechanical systems are
> first defined referencing available construction documentation. From
> there, a brief review of “as-built” documentation (including submittals)
> should highlight some initial variances for evaluation.
>
> - For the intended/stated purpose: developing a performance
> rating well before actual operations can be known, 90.1/Appendix G (in
> combination with the additional requirements of LEED and rigor of GBCI
> simulation review) is a fine option. Analogous standards I’ve worked with
> do some things better and some things worse, and there will likely always
> be room for improvement, but for all that we talk of problems/holes in the
> standard as applied to the “real world” of modern building design, the
> standard covers quite a bit well enough.
>
> - “Design phase” modeling, inclusive of the Appendix G protocol,
> is perhaps most critically useful in determining *relative* (not
> absolute) performance for design alternatives to inform the design
> process. In my experience, it’s a slippery slope to quantify design
> alternatives in terms other than relative % performance increases.
> Presenting such results in terms of $$$ savings supports the fallacy that
> such early results are founded upon something other than a broad range of
> (probably incorrect) assumptions. This is not a comfortable concept for
> most to grasp, but energy simulations are sometimes at their most
> informative when they are “wrong.” I have found it a difficult issue to
> explain for those outside our field, so I usually try to guide
> conversations around such sticky matters. The broader point I am trying to
> make in this bullet is that “relative” performance metrics have a distinct
> value from absolute cost predictions, and relative metrics translate better
> into informing the design process. Maybe someone else can make the point
> more eloquently… ?
>
>
>
> I hope that adds to the discussion for some =)!
>
>
>
> ~Nick
>
>
>
>
>
> *NICK CATON, P.E.*
> *Owner*
>
>
>
> *Caton Energy Consulting*
> 1150 N. 192nd St., #4-202
>
> Shoreline, WA 98133
> office: 785.410.3317
>
> www.catonenergy.com
>
>
>
> *From:* Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] *On
> Behalf Of *Alfonso Hernandez
> *Sent:* Thursday, May 21, 2015 8:34 AM
> *To:* Maria Karpman; 'Brooks, Alamelu'; 'Jim Dirkes'; 'Nathan Kegel';
> Jacob Dunn
>
> *Cc:* bldg-sim at lists.onebuilding.org
> *Subject:* Re: [Bldg-sim] Comparing ASHRAE 90.1 App G Models to Real
> Buildings
>
>
>
> Jacob et al:
>
>
>
> Some more points to the mix:
>
>
>
> 1) Increased infiltration/exfiltration due to seasonal changes in wind
> patterns, which mostly affect high-rises, is not modeled very often. The
> changing nature of wind (more or less cold or hot wind coming from a given
> direction) will affect cooling and heating loads.
>
>
>
> 2) Not every software can model the thermal mass of concrete or brick.
>
>
>
> 3) Microclimatic conditions (the urban overshadowing Jacob was mentioning)
> have to do also with air movement (urban canyon effect), and are not
> modeled often.
>
>
>
> 4) Buildings with Occupancy/Vacancy sensors are usually not modeled with
> accuracy. App G just gives a 10% LPD reduction when using them (in theory
> you could model them if you know the exact patterns of occupancy before
> construction, which never happens).
>
>
>
> 5) Daylight Harvesting and Electrochromic glass are too dynamic systems to
> be modeled accurately (unpredictable occupancy again).
>
>
>
> However, I do agree with Prof. Reinhart about calibrating design models
> with as much real time data as possible. That way we could recreate other
> scenarios (climate change, systems decay, the impact of a change of
> occupancy, etc.).
>
>
>
> *Alfonso E. Hernandez, LEED AP*
>
> *Kirksey* | Architecture
>
>
>
> *From:* Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org
> <bldg-sim-bounces at lists.onebuilding.org>] *On Behalf Of *Maria Karpman
> *Sent:* Thursday, May 21, 2015 9:55 AM
> *To:* 'Brooks, Alamelu'; '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
>
>
>
> 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
>
>
>
> --
>
> *Maria Karpman *LEED AP, BEMP, CEM
>
> ________________
>
> Karpman Consulting
>
> www.karpmanconsulting.net
>
> Phone 860.430.1909
>
> 41C New London Turnpike
>
> Glastonbury, CT 06033
>
>
>
> *From:* Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org
> <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
>
> 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] *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
>
> Website <http://buildingperformanceteamcom>l LinkedIn
> <https://www.linkedin.com/pub/jim-dirkes/7/444/413>
>
> 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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--
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
Website <http://buildingperformanceteamcom>l LinkedIn
<https://www.linkedin.com/pub/jim-dirkes/7/444/413>
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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