[Bldg-sim] Comparing ASHRAE 90.1 App G Models to Real Buildings
Nicholas Caton
ncaton at catonenergy.com
Thu May 21 10:44:11 PDT 2015
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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