[Equest-users] Actual Building Energy Cost

[David Bastow]

Of course, your fee reflects the amount of accuracy the client is
requiring you to have.  Some clients might only expect 5-20% accuracy,
and of course you would provide them with a lower fee.  However, in over
17 years of running hourly, climate history based, energy estimating
software, (not always eQUEST), I don't ever remember doing a study where
we were satisfied with being more than 5% off on our final base model.
If you are happy with being 25% or more off, then why even do a model,
you might as well just guess or do some kind of energy saving hand
calculation.  The fun part is getting modeled gas usage and electrical
usage, month to month, to follow historical monthly trends and still be
close to the annual energy usage on both.  When you get both the annual
energy usage and the monthly energy usage of gas and electric close to
historical usage, then that's when you feel good about your base model
to compare against ECM runs.
 
No one said this was easy.  That's why you earn ever dime of your fee.
Your first preliminary base model run, if you do a good job, might be
5-20% off historical usage.  To even get that close normally requires an
extensive survey, documenting ever identifiable energy using item,
interviews regarding usage by the occupants and maybe even data logging
usage of some important items, to confirm actual usage.  It can,
depending on the size and complexity of the modeled building, take
several days to a week or more and a hundred or more runs to just create
a good solid base model, that reflects historical usage.  That's why
modeling a new building, without any historic energy usage data to
match, other than approximate BTU's per square foot, is a piece of cake.

 
David A. Bastow 
McClure Engineering, Inc.  

________________________________

From: Eric O'Neill [mailto:elo at MichaelsEngineering.com] 
Sent: Wednesday, June 16, 2010 3:52 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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