[Equest-users] Actual Building Energy Cost

[Nick Caton]

While I (and I am sure many others) have books to write regarding my
thoughts on the topic, I think I might suggest a simple step back:  The
concept of predictively modeling to within a few percentage points of
accuracy is ridiculous.  There are simply way to many things that could
not be known.  HOWEVER:  The concept of building a model for an existing
building, whose modeled energy consumption/costs fall within a 1-2% of
historical utility records, is entirely feasible - and a reasonable
requirement if the goal is to generate a model for predictive purposes.
How often such predictive models' accuracy is misinterpreted is
something I get depressed to think about.

 

I haven't done the DOE-modeling work that's being referenced with such
requirements, but I have done work for educational clients
(physics/building science departments) who wish to get these models set
up for ongoing study/tweaking purposes.  The exercise is challenging,
and as close as energy modeling gets to "fun," when you can rest at ease
knowing the client is fully on board with what the model is and isn't.  

 

It's fully rational to squirm and cringe when you have to make models
that you know will be mis-used and mis-understood, despite your best
efforts.  Fortunate is the practicing energy modeler who gets to work
for fully educated clients and design teams all the time =).

 

Rather than drill David, I think it would be safe to assume those DOE
requirements exist to calibrate a model to a given degree to whatever
historical records are available, NOT to mandate a level of accuracy for
predictive purposes.  If I'm wrong, I hope that work never crosses my
desk!

 

~Nick

 

 

NICK CATON, E.I.T.

PROJECT ENGINEER

25501 west valley parkway

olathe ks 66061

direct 913 344.0036

fax 913 345.0617

Check out our new web-site @ www.smithboucher.com 

 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Eric
O'Neill
Sent: Wednesday, June 16, 2010 4:52 PM
To: David Bastow; aazhari at jainconsultants.com;
equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Actual Building Energy Cost

 

How much effort was put into minimizing the error of your inputs to
justify that level of accuracy in your output? For example, did you
convert real weather data for the two years and use an average of the
simulations? Were you modeling small buildings so you could get a fairly
reasonable infiltration rate empirically? Were occupancy schedules
trended, and for how long? Were all the systems and controls working
correctly, with all sensors calibrated regularly? 

 

1 to 2% seems to me to be fairly unreasonable. Unless you do an amazing
job verifying your inputs, in my opinion that level of precision doesn't
get you a better model. If you set everything up as best you can and it
comes in there, great! But a correctly set up model can be off by over
2% because of a couple "El Nino" years, a facilities guy locking a
humidity high limit to 50% for a summer, or any number of operational
factors. On the other side of it, we've tried to match a simple DOE2.2
model to a DOE2.1e model with limited success (I don't think we got
within 3%, although we didn't spend too much time with it). Who knows
what the difference would be with E+.

 

I know I always squirm when I'm asked to do existing building models,
and it may be irrational. Heck, if the DOE is asking for 1-2%, I
probably am being irrational. But it seems to me that the error from
assumptions could easily swing a model 1-2% (what would a 30% error on
your infiltration do to an otherwise correct building?). What are other
people's thoughts? 

 

Eric

 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of David
Bastow
Sent: Wednesday, June 16, 2010 3:48 PM
To: aazhari at jainconsultants.com; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Actual Building Energy Cost

 

On all the DOE modeling projects that we have done, of an existing
building, they have required the model to be within 1 to 2% or less of
the actual energy usage, based on an average two year history.  Is that
what you are talking about?

 

David A. Bastow 

McClure Engineering, Inc.  

 

 

________________________________

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Ahmed
Azhari
Sent: Wednesday, June 16, 2010 12:10 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Actual Building Energy Cost

Hi all, 

 

Does anyone have a ballpark percentage of the actual annual energy cost
versus the modeled annual energy cost for a building?  

 

Thanks,

________________________________________________________________________
__

Ahmed Azhari, B.Eng., LEED(r) AP

Energy Analyst

 

Jain Sustainability Consultants Inc.

 

2260 Argentia Road, 2nd Floor

Mississauga, Ontario L5N 6H7, CANADA

Tel:  (905) 542 7211 Ext 234

Fax: (905) 542 7622

Email: aazhari at jainconsultants.com <mailto:aazhari at jainconsultants.com> 

Web: www.jainassoc.com <http://www.jainassoc.com/> 

 

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