[Bldg-sim] eQuest - Model verification
Jorge Torres-Coto
jtorres-coto at mbo1.com
Fri Apr 29 07:48:53 PDT 2011
5% is a really tight number we have been forced to work with on come retro
commissioning projects in the past, with 10% being the norm on an annual and
monthly basis for overall building energy use. Anything stricter than those
numbers is unrealistic (again for the overall building).
Jorge E. Torres Coto
4830 Viewridge Ave.
San Diego, CA 92123
p 858.751.0933
f 858.751.0937
c 858.688.6088
_____
From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Nick Caton
Sent: Friday, April 29, 2011 7:42 AM
To: James V Dirkes II, PE; Karen Walkerman; Carol Gardner
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] eQuest - Model verification
I know I have less experience calibrating models than some other
respondents, but I'll share my perspectives as well:
It is easy to adjust occupancy schedules / lighting loads in eQuest, but it
requires the end-user knows the program. If the end-user is inexperienced
with eQuest or any other simulation program, then there is no "easily
modifiable" model you can provide.
1) Even if I manage to put in daily occupant and fan schedules based on
actual use, will the model be accurate enough to take me within 1%?
With regard to historical modeling, showing any deadband of accuracy to
known costs/consumptions is *technically* possible given enough information
and time. That said, falling within 1% of any holistic measure, even on an
annual basis, before "refining the unknowns" would probably happen only by
very lucky/happy coincidence. It's fair to say that in a relative sense,
some buildings operate much more regularly and predictably than others, and
for these cases you or a client might reasonably expect a tighter deadband.
Asking what is "accurate enough" is like asking "what's reasonable," and the
answer is that it depends on what info/time you have. There are always
"unknowable" variables that can play a big role in your end-results
(example: what is the actual leakiness of a 35 year old envelope?).
2) We have been asked to remove plug loads (both for consumption
purposes and cooling loads). Will this be too big of an assumption to get
any accuracy out of the model in the future?
Depends on your building, but for most buildings plug loads are a
significant fraction of consumption/internal loads.
3) How do I modify the weather input file?
I saved the attached email from David Reddy for the next time I need to
tackle "actual weather." My attempts thus far haven't been terribly
successful, so I have no "go-to" procedures to share just yet. I have heard
reference from those who appear in the know to macro/VBA-heavy excel
spreadsheets which can automate the workflow to one extent or another, but
I've not yet seen one with my own eyes. I have yet to hear of any program
that can "easily" incorporate recently recorded weather data.
4) Are there any other ideas I'm missing that will help us validate a
model as an absolute measure of actual building energy consumption?
Generally: the only "absolute measure of actual building consumption" will
be the utility bills. Something about the 1% number tells me you or your
client might be trying to hammer a nail with a screwdriver. Energy models
are great for looking to the past to make decisions that acknowledge the
unknowns of the future, but if the real goal is to know the actual energy
usage on an hourly basis - why not set up some sub-meters and track them?
While meters/bills measure energy usage and energy models can use that
information to make predictions, models don't determine bills - it doesn't
work in reverse!
PS: For all the work you might put into calibrating a model with historical
weather and other known data, keep perspective that your model will only
ever be that accurate for behaviour in that year. The moment anyone wants
to use this model predictively (for the future), you probably should swap
back to TMY weather data and embrace the inherent unknowns.
~Nick
cid:489575314 at 22072009-0ABB
NICK CATON, E.I.T.
PROJECT ENGINEER
Smith & Boucher Engineers
25501 west valley parkway
olathe ks 66061
direct 913 344.0036
fax 913 345.0617
www.smithboucher.com
From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of James V Dirkes
II, PE
Sent: Thursday, April 28, 2011 7:12 PM
To: 'Karen Walkerman'; 'Carol Gardner'
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] eQuest - Model verification
Weighing in late on this..
If I get >80% R-squared correlation, I think I'm doing well!
There are so many unknowns, including the normal situation that the client
doesn't know their own operating schedules, occupancy patterns, or
maintenance / calibration procedures..
The Building Performance Team
James V. Dirkes II, P.E., LEED AP, BEMP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616 450 8653
From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Karen Walkerman
Sent: Thursday, April 28, 2011 3:31 PM
To: Carol Gardner
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] eQuest - Model verification
Also, a model that is calibrated to actual building use and weather can help
to highlight building operation issues. I have had models which were off
from actual operating energy use that I was able to determine how the
building was operating inefficiently.
In one case, I created a model of an existing building. For this model, I
made an actual count of lighting fixtures and computers. For most of the
year, there were few other electrical loads. I based on their occupancy and
use schedules, I was not quite able to calibrate the electrical energy use.
When I met with the client, I informed him that my model showed somewhat
lower electrical use, equivalent to 1/3 of the computers remaining on
24-hours per day. As it turned out, about 1/3 of the employees DID leave
their computers on at all times so that they could log in remotely.
... I guess what I'm saying is that maybe the goal is not to get the model
within 1% of the building energy use, but get the building within 1% of the
model.
--
Karen
On Thu, Apr 28, 2011 at 3:20 PM, Carol Gardner <cmg750 at gmail.com> wrote:
Bill summed it up really well, Katherine. Sometimes a client will think a
calibrated model must match the real building by an unrealistically high
number, like 1%. I really can't imagine an instance when that would be
desirable. It certainly would be costly to achieve.
Usually the plan is to use the calibrated model as a tool to examine various
energy saving measures/opportunities that the client may be interested in
implementing. It is important to remember, in this case that you are looking
at the usage between the calibrated model and the ECM model, so the 1%
deviation is consistent in both and not a worry.
Carol
On Thu, Apr 28, 2011 at 12:03 PM, Bishop, Bill <wbishop at pathfinder-ea.com>
wrote:
Katherine,
The questions I would have for you (or your client) are:
* Is this an existing building, or something in the design phase?
* What is the model going to be used for?
* Is there something magical about the 1% number?
* 1% of what? Annual electrical consumption? Annual gas consumption?
Both? Monthly electric/gas consumption? Monthly/annual electrical demand?
* Why remove the plug loads? Even if everything else is modeled
perfectly, plug loads are typically 10% or more of annual electrical
consumption but can be all over the place.
* "Easily adjusted" by whom? Does your client want you to hand them
a model and let them make all subsequent adjustments?
Even if you are an expert energy modeler, and there is monitored energy data
available for the building down to the individual electrical panels or
broken out by end use (lighting, plug loads, individual HVAC units etc.) you
will be hard-pressed to get to within 1% on a month-by-month basis. Even 5%
month-by-month is difficult. Sure, you can tweak to your heart's content to
get a model to match annual electric consumption within 1% based on prior
year's utility bills but to maintain a calibrated model to that tolerance
after that would require a lot of work.
I suggest searching the bldg-sim and equest-users archives for information
about weather files.
Oh, one more question - how much money does your client have?
Regards,
Bill
William Bishop, PE, BEMP, LEEDR AP | Pathfinder Engineers & Architects LLP
Mechanical Engineer
Error! Filename not specified.134 South Fitzhugh Street
Rochester, NY 14608
T: (585) 325-6004 <tel:%28585%29%20325-6004> Ext. 114 F: (585)
<tel:%28585%29%20325-6005> 325-6005
wbishop at pathfinder-ea.com www.pathfinder-ea.com
<http://www.pathfinder-ea.com/>
P Sustainability - the forest AND the trees. P
From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Katherine
Louman-Gardiner
Sent: Thursday, April 28, 2011 1:49 PM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] eQuest - Model verification
Hi All,
Our client would like us to produce an eQuest model that
a) Can be easily adjusted to include current and recently recorded
weather data
b) Can be easily adjusted to reflect space occupancies and lighting
loads
c) Will reflect the actual building energy usage to within 1%
Do any of you have experience trying to validate models like this?
My concern is that models are approximations, and will not account for small
changes in occupancy, outdoor weather, etc.
I guess my questions are these:
1) Even if I manage to put in daily occupant and fan schedules based on
actual use, will the model be accurate enough to take me within 1%?
2) We have been asked to remove plug loads (both for consumption
purposes and cooling loads). Will this be too big of an assumption to get
any accuracy out of the model in the future?
3) How do I modify the weather input file?
4) Are there any other ideas I'm missing that will help us validate a
model as an absolute measure of actual building energy consumption?
Thank you for your help,
Katherine
Katherine Louman-Gardiner, EIT
Mechanical Engineer
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