[BLDG-SIM] Help calibrating eQuest building model

Neuhauser, Ken Ken.Neuhauser at csgrp.com
Thu Nov 29 12:14:30 PST 2007


Seun-

I think John has a point that you might be using too much internal
gains.  Typical guidelines/defaults for internal loads are usually aimed
at solving questions of design loads and not operational consumption
over a period of time.  So check that your plug and lighting loads are
reasonable.  If you're absolutely obsessed with detail, you would use
sub-metering data for lights and equipment to compare the kWh over a
period to the result of your schedules and power density over an
equivalent period.  Alternately, a simple survey (with spot metering) of
equipment draw and estimates of operating schedules should get you close
enough.  

 

One thing that has been missing from the discussion is infiltration.
This could well be the most significant variable - especially in your
heating climate.  It is generally ignored in simulations and most
engineering calculations because it is a real bugaboo - very difficult
to define.  But it may be possible to "bracket" the infiltration.  There
are a couple of ways that you could estimate or assess the infiltration
performance of the actual building.  Tracer gas testing could give you a
quantitative measure of actual air changes under the conditions of the
test.  The difficulty in this method is translating the results of the
test under the specific test conditions to estimates of what might
happen under other conditions.  To use tracer gas infiltration data in
the model, you would use an infiltration method that responds to outdoor
temperature and, probably wind, and then determine what values for other
parameters are needed in DOE2 to arrive at a similar calculation of
infiltration (or air changes) in the simulation under simulation weather
conditions that correspond to those of the test.  

Perhaps a simpler method would be to use fan pressurization testing to
estimate the leakage characteristics of the building enclosure.  You can
then give DOE2 corresponding inputs describing the leakage
characteristics of the building enclosure (whether the algorithms within
DOE2 will produce reasonably accurate estimates of infiltration from
these is another story.)

Lastly, you could do what some un-named parties in the building modeling
world advocate and just adjust the infiltration lever in the model until
the model results match the measured results.   

 

All in all, having been tied to a chair doing DOE2 runs in a windowless
basement lab as a graduate student myself, I think it worthwhile to pass
along wisdom that a very pragmatic engineer offered to me: "The model is
a representation of reality.  It is not reality."  In other words, the
model is only a mathematical representation of what is happening
thermodynamically within the building.  

Or, in the immortal line from Monty Python's "The Holy Grail" (King
Arthur's page) "It's only a model."

Best regards,

Ken

 

Ken Neuhauser, M.Arch, MSc.Arch, LEED AP

Architectural Project Manager

Conservation Services Group, Inc.

40 Washington Street

Westborough, MA 01581

Ph. 508 836-9500 ext. 13226

Fax 508 836-3181

www.csgrp.com <http://www.csgrp.com/>    

 

 

 

________________________________

From: BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com] On Behalf Of Seun
Odukomaiya
Sent: Thursday, November 22, 2007 8:53 PM
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] Help calibrating eQuest building model

 

Hello,

My name is Seun Odukomaiya. I am a graduate student at Purdue University
working on the Building Sciences. As part of my research, I am trying to
calibrate an eQuest model to match the energy performance of an actual
building for which i have data. Currently, I am having difficulties with
the electric heating element. The actual building (and thus the model)
utilizes an electric heating element. The energy data from the model,
however, is much lower than that of the actual building. I have tried
several things, but have been unsuccessful in increasing the energy
consumption of the electric heating element in my eQuest model. I need
to increase the energy consumption of the electric heating element in my
eQuest model to get it to match the data from the actual building. Any
help in ways to accomplish this within eQuest would be so greatly
appreciated. Thank you in advance.

 

Seun Odukomaiya

Mechanical Engineering Technology

Purdue University

 
 
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