HI All
I am trying to create same model in equest and energy plus to see whether i
see same results and just to validate my simulation files.
has anyone done this before?
I would like to know what is the % difference in both software outputs?
Thanks
Deepika
equest and energy plus outputs
Apr 27, 2011
I was involved in a two year project 2005-2007 to convert the Calif.
Energy Commission's Title-24 certification suite of building tests from
DOE-2.1E to EnergyPlus. There are some areas where it's difficult to
get comparable inputs due to differences or limitations in the models.
The differences between the two programs varied a lot depending on the
building, weather, and HVAC system. For the CEC certification suite of
160 runs, cooling results were more consistent, within 10% in most
cases, with EnergyPlus almost always on the high side; for heating, the
differences were much greater, sometimes with EnergyPlus being 40-60%
lower than DOE-2.1E. I have a 120-page report on this comparison, but
haven't bothered to put it on the Web.
Joe Huang
Thanks Joe
Even I realized the same thing. the total energy use in Energy plus was
almost 50% less than equest.
If this is the case, who would you know that you model is working fine?
Hmmm- an energy plus model showed 50% less energy use (EUI) than eQuest?
Did you use the same weather files? (i.e. convert the EPW you used in E+ to
.bin and use the same weather file in eQuest?)
If this is truly the case, this is unsettling as a simulator. Wouldn't it
be safer for our clients to error on the conservative side and give the
eQuest results instead of the E+ results?
Also--if this is the case, then what is the market advantage to spending
thousands of dollars on E+ software rather than use the FREE-ware eQuest
program??
I'd appreciate any commentary to help me "see the light" of this topic. And
if Deepika is willing to share a visual of his energy results output, I'm
super curious to see what it is showing...
Good question/good info...thanks,
Pasha
I thought E+ is a free program? I would be interested to hear from anyone who
has used Google SketchUp and the Open Studio Plug-in to generate a 3D view in
E+.
I would like to hear more about the discrepancies between eQuest and E+ from
those who use both programs.
Paul Diglio
As Joe and others mentioned, its really difficult to create all parameters
same in both softwares.
I am still working on it .
For ex, which system should I use in equest as equivalent to unitary system
in E+?
I understand its difficult to match every input and hence, getting same
results is very tricky.
Thanks all for their inputs
I am sure EnergyPlus is a fine and well thought out program (consider the
sources and fine people involved).? However, since I am in production mode (and
don't have time to create a model in two different programs-who pays for THAT),
I chose to migrate to eQuest after DOE-2.1 A, B, C, D, and E. There are plenty
of resources to ask questions of, the program started out in Windows (didn't
need "add ons"), and gives me a 3-D rendering on the building immediately.
I dealt with 20 years of "raw" DOE-2, where?I didn't know what my building
really looked like (until Joe Huang came along with BDL Draw..). So I would need
at age (you guess..) to not relearn an entirely new program and stick with what
I had learned over the past 25+ years.
John R. Aulbach, PE, CEM
So based on my analysis, there is a difference of about 10% in results of
equest and E+. I would believe that because there are certain parameters
which are very difficult to match.
this seems reasonable to me.
As I understand it--Energy+ is free-ware in it's raw form. I guess I was
wrong to make an assumption that Deepika is using it without an
interface. If this is not the case it might explain such a variance in
results. When I model in DOE-2 raw form---it is so much harder for me to
manage my data and inputs in my head and such----I was not born to be a
programmer, and it gives me nightmares from struggling to pass FORTRAN so
many years ago...ugh.
Therefore, I haven't looked at E+ myself for a very long time and purchasing
or putting out the cost for the user-interface programs is not as desireable
as using the eQuest free-ware. or the future CANQuest free-ware (future SI
version).
BUT-- I know that E+ is supposed to have some great capabilities in which we
are limited with DOE-2 (to an extent.) Has anyone else had the time and
desire to compare these program engines more closely recently? Also--why
is it so difficult to "match" systems in eQuest and E+....forgive my
blase'-ness, but isn't a pkgd system a pkgd system...a pkgd system??? :)
Pasha
This was a little study I did out of curiosity last year, and the
results between eQUEST (v3.63) and EnergyPlus (v4.0) matched quite well
(~1.4% difference). All the schedules, zone areas, surface areas were
exactly the same (I checked), but I also chose a simple system; PTAC
units for the comparison. I believe when I was doing this I had checked
the performance curves that were being used in EnergyPlus and they
matched the eQUEST curves.
I assume the results will begin to differ when the systems become more
complicated, but even then I believe if both models are calibrated to
match as much as possible the results shouldn't vary significantly
(assuming all systems are native to the programs and we're not creating
work-arounds i.e. DOAS in eQUEST using dummy zones or the like).
(FYI, the geometry was ported over to EnergyPlus through a tool I wrote
using Excel and VBA, but it's a messy process)
Following are some of the results and graphical outputs:
____________________
Mirza Sajjal
Mizra:
Thank you for the time it took you to send the results of your study to the
forum. Some of the top simulation firms in my area use Energy Plus and I was
confused when other people claimed a higher discrepancy rate than you modeled.
Paul Diglio
I did not think my previous reply to Deepika would engender so much
traffic on this topic, but after reading through the various posts
I feel compelled to add further comments because I think there's been
some misunderstanding or misperceptions abou comparing results between
two programs, in this case, specifically EnergyPlus and eQUEST or DOE-2:
1) Several people (some even in private e-mail) have mentioned looking
at the BESTTEST or SP-140 test runs that are repeated everytime there's
a new EnergyPlus release. Those simulations are extremely simplified
test cases, mostly of one-zone models designed to test fundamental heat
transfer algorithms - the impact of solar gain, wall heat loss, thermal
mass - across various programs. These test cases
do not begin to address the dynamic conditions found in any real
building, particularly not a large commercial building. Unfortunately,
it's
these interactions between the transient loads and the HVAC system
response that will color or dominate the resultant energy numbers.
In my opinion, a far more revealing test suite would be either the CEC
Title 24 certification test suite or even the ten DOE-2 sample runs,
where the models are of realistic buildings with typical systems and
operating controls (for more details on the Title-24 certification test
suite, please see my SimBuild 2006 paper, available for download at
http://www.wbt/downloads/SimBuild2006_EPlusDOE2_translatorF.pdf ). My
point is that the BESTTEST/SP140 results may show that the basic heat
transfer algorithms in the programs are (reasonably) consistent, but
that doesn't mean the programs will show similar results when used to
model actual buildings, particularly not commercial buildings with
intermittent operations and complex HVAC systems and controls.
2) Several people sounded incredulous that the differences could be as
much as 50%. I can only say that if you try it, i.e., model the same
building (preferably not a shoebox with a window on one side :-)) with
two programs, you will quickly appreciate the difficulty. Actually, from
my vantage point, 50% does not sound exaggerated at all. I just got back
from a simulation workshop in China, where differences of several
hundred percent were reported comparing programs such as DOE-2.1E,
TRNSYS, and DeST, a Chinese program, even though they were looking only
at residential apartment buildings. The dirty secret in our field is
that even if you asked two reasonably competent modelers to model the
same building with the same program, they're apt to come up with quite
different results. Doing it with two different programs just makes that
match exponentially more difficult.
3) Several people (including me) have alluded to the difficulty in
making the inputs consistent. I cannot emphasize this enough. All
programs have hundreds of hidden defaults or assumptions that aren't
necessarily transferable. My paper highlights nine of the most prominent
ones found in the CEC project, e.g., DOE-2 models drapes as a
SHADING-FRACTION, EnergyPlus models them as internal shading surface
requiring 10 inputs; DOE-2 allows a distribution loss in the water loop,
EnergyPlus didn't; DOE-2 degrades the wind speed in its infiltration
calculation, EnergyPlus didn't; DOE-2 allows a thermostat throttling
range; EnergyPlus didn't; etc., etc. (some of these limitations in
EnergyPlus may have been corrected since 2007). Since I had access to
both the DOE-2 and EnergyPlus source code at the time, I believe I did
the most thorough job possible in matching inputs, but even so I had to
"punt" in numerous places (no drapes, infiltration at raw wind speed,
etc.) for the sake of an "apples-to-apples" comparison. Yet, even under
these ground rules, I was still seeing up to 40% differences in heating
loads in some cases.
4) So which are the correct, or better, results? I really can't say.
When you look into the codes, there is room for questioning the solution
techniques in both programs. Just by dint of having seen many more DOE-2
results, I tended to regard them as the "conventional wisdom", but then
conventional wisdom could always be wrong. Maybe we have been
overestimating the heating energies in California all these years. After
reading through this litany of problems, some may want to throw up their
hands and say either, "it's hopeless" or even, "who cares?". That to me
is a wrong and dangerous response, because it ultimately damages the
credibility of simulations. Going back to China, many experts there have
become disenchanted and distrustful of simulations, and are calling for
it NOT to be used for compliance calculations. The same can happen here,
as well. So, I think we need to spend more effort to have a better sense
of the relative performance of different programs, and what is the
"ground truth". Doing a parallel set of calibrated simulations against
good monitored data would be a good start.
Joe Huang
Please note that the link for my paper should be
http://www.whiteboxtechnologies.com/downloads/SimBuild2006_EPlusDOE2_translatorF.pdf,
not what was written below. Sorry for the mistake.
Joe Huang
DOE2 and EnergyPlus
I would like to see the results of DOE21E (or eQUEST / DOE22) and EnergyPlus compared with the following two projects. They are similar to real projects but modified and simplified for teaching purposes.
Middle School & Community Center (150,000 sf approx.)
http://bepan.info/proj-bldgs/p12-middle-school
High-Rise - Multi-Use Building (1,000,000 sf approx.)
http://bepan.info/proj-bldgs/p13-high-rise-bldg
Has a building of the size and scope of the 160-storey Burj-Dubai (Burj-Khalifa project analyzed by TRACE) been analyzed with EnergyPlus? See facts and figures
http://www.burjkhalifa.ae/the-tower.aspx
How about a full university campus with one central plant?
In my opinion EnergyPlus needs to remove (or make optional) the features that increase execution time. See attachment USDOE Energy-Programs - DOE21E and EnergyPlus
Why should a private firm develop an interface to EnergyPlus after USDOE left all the developers of interfaces to the DOE21E stranded? There is no money to be made from the engineering software business. Development costs of graphics and forms interface costs are much higher than engineering analysis, but small compared to the marketing, support and training costs. There are few customers for engineering software and they expect to pay about $50 to $500 which is typical of commercial software products.
Varkie
=================================================
Sent Thursday, April 28, 2011 8:12 pm
To Paul Diglio
Subject Re: [Equest-users] equest and energy plus outputs
I did not think my previous reply to Deepika would engender so much traffic on this topic, but after reading through the various posts I feel compelled to add further comments because I think there's been some misunderstanding or misperceptions about comparing results between two programs, in this case, specifically EnergyPlus and eQUEST or DOE-2:
1) Several people (some even in private e-mail) have mentioned looking at the BESTTEST or SP-140 test runs that are repeated everytime there's a new EnergyPlus release. Those simulations are extremely simplified test cases, mostly of one-zone models designed to test fundamental heat transfer algorithms - the impact of solar gain, wall heat loss, thermal mass - across various programs. These test cases do not begin to address the dynamic conditions found in any real building, particularly not a large commercial building. Unfortunately, it's these interactions between the transient loads and the HVAC system response that will color or dominate the resultant energy numbers.
In my opinion, a far more revealing test suite would be either the CEC Title 24 certification test suite or even the ten DOE-2 sample runs, where the models are of realistic buildings with typical systems and operating controls (for more details on the Title-24 certification test
suite, please see my SimBuild 2006 paper, available for download at
http://www.wbt/downloads/SimBuild2006_EPlusDOE2_translatorF.pdf ).
My point is that the BESTTEST/SP140 results may show that the basic heat transfer algorithms in the programs are (reasonably) consistent, but that doesn't mean the programs will show similar results when used to model actual buildings, particularly not commercial buildings with intermittent operations and complex HVAC systems and controls.
2) Several people sounded incredulous that the differences could be as much as 50%. I can only say that if you try it, i.e., model the same building (preferably not a shoebox with a window on one side :-)) with two programs, you will quickly appreciate the difficulty. Actually, from my vantage point, 50% does not sound exaggerated at all. I just got back from a simulation workshop in China, where differences of several hundred percent were reported comparing programs such as DOE-2.1E, TRNSYS, and DeST, a Chinese program, even though they were looking only at residential apartment buildings. The dirty secret in our field is that even if you asked two reasonably competent modelers to model the same building with the same program, they're apt to come up with quite different results. Doing it with two different programs just makes that match exponentially more difficult.
3) Several people (including me) have alluded to the difficulty in making the inputs consistent. I cannot emphasize this enough. All programs have hundreds of hidden defaults or assumptions that aren't necessarily transferable. My paper highlights nine of the most prominent ones found in the CEC project, e.g., DOE-2 models drapes as a SHADING-FRACTION, EnergyPlus models them as internal shading surface requiring 10 inputs; DOE-2 allows a distribution loss in the water loop, EnergyPlus didn't; DOE-2 degrades the wind speed in its infiltration calculation, EnergyPlus didn't; DOE-2 allows a thermostat throttling range; EnergyPlus didn't; etc., etc. (some of these limitations in EnergyPlus may have been corrected since 2007).
Since I had access to both the DOE-2 and EnergyPlus source code at the time, I believe I did the most thorough job possible in matching inputs, but even so I had to "punt" in numerous places (no drapes, infiltration at raw wind speed, etc.) for the sake of an "apples-to-apples" comparison. Yet, even under these ground rules, I was still seeing up to 40% differences in heating loads in some cases.
4) So which are the correct, or better, results? I really can't say. When you look into the codes, there is room for questioning the solution techniques in both programs. Just by dint of having seen many more DOE-2 results, I tended to regard them as the "conventional wisdom", but then conventional wisdom could always be wrong. Maybe we have been overestimating the heating energies in California all these years. After reading through this litany of problems, some may want to throw up their hands and say either, "it's hopeless" or even, "who cares?". That to me is a wrong and dangerous response, because it ultimately damages the credibility of simulations. Going back to China, many experts there have become disenchanted and distrustful of simulations, and are calling for it NOT to be used for compliance calculations.
The same can happen here, as well. So, I think we need to spend more effort to have a better sense of the relative performance of different programs, and what is the "ground truth". Doing a parallel set of calibrated simulations against good monitored data would be a good start.
Joe Huang