Dear Tuan,
Please observe the
following things that might explain you the anomaly.
The simulation time is
different in cases (i.e. 5.58 seconds for Case 1A and 5.73 seconds for Case
1B). This leads to a conclusion that there are some convergence issues
with the heat balance algorithms. I quickly made few runs and found that you
are right in saying that the results are different even if you force feed the
zone volume and surface areas etc. the value are still different. So this made
me understand your problem.
Now guess what is changing
it...... though everything is similar!!!
Before I come to that, I
also observed that you modeled the gable roof (the slanted roof portion) by
just a reflective shade.... whereas the standards practice is that you make it
a zone (a thermal zone) to see the heat interaction between the zones
effectively.
Coming back to the point,
this is good case of error accumulation over time. I made a run without your
roof shades and the results are exactly similar to few decimal places for both
the cases ( i.e. Case 1A, Case 1B).
Then, I checked your DXF
output closely by overlapping it in Auto Cad. It was observed that there are
differences after few decimal places and somehow the translation by the
rotation matrix used by energy plus internal engine and the translation of your
Geometry building software is different. This is evident if you see the output
after three decimal places or so at certain vertices.
Now letâ??s talk about the
Sun, the cooling and heating is directly dependent on sun movement, even up to
a millimetre will show up the change over 8760 ("4" as your Sub
hourly time step) hours of calculation. Therefore to ascertain this, remove
your shades and verify the logic. Even if you have lesser WWR, your change in
energy accumulation will not be as significant as it is in this model.
I hope that give you an
idea of how to remove or by pass this anomaly if you are up for some tough
accuracy goals.
With regards,
SMH Adil
Simulation Specialist - Built Environment
Certified Energy Manager, Founding Member IBPSA, INDIA
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Energy Design
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Floor, D-15 A.F Enclave ? 1, Jamia Nagar, New Delhi, 110025, Tel: ++91 11
24537371| Fax: +91 11 29948146| Mob: +91 9873588571, Web: www.geedindia.org, www.firedynamics.in, Skype Id: smh.adil,
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Modeling|Air Flow, IAQ,
Fire/Smoke for NFPA 130 Tenability & Thermal Modeling|Evacuation
& Agent Based Egress Simulations | Design Assistance in Passive
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On Monday, 18 November 2013 1:50 PM, Jeremiah Crossett <jcrossett@xxxxxxxxxxxxxxx> wrote:
Did you try to use DIFF software such a http://www.araxis.com/merge/index.en or comparable? You might compare your grasshopper file to an E+ example to see if you can find some difference, it sounds like grasshopper may be using some unexpected GlobalGeometryRules
Starting Vertex Position UpperLeftCorner
Vertex Entry Direction Counterclockwise
Coordinate System Relative
Daylighting Reference Point Coordinate System Relative
Rectangular Surface Coordinate System
On Sun, Nov 17, 2013 at 11:54 PM, <tranhuuanhtuan2004@xxxxxxxxx> wrote:
Hi Jeremiah,I replicated a idf file to create two models. One is oriented to a certain angle simply by changing the Norht axis in the idf file (e.g. anpha). The other one is absolutely oriented by rotating entire the building using Grasshopper in Rhino (for 360-anpha).So basically these models are identical. But the outputs are different which doesn't make any sense.I did upload the idf files in the earlier messages so you could test it out. This problem did not happen for a single case so I am also trying to investigate. I am testing two approaches for the full circle to see how they are different and will post it here.Thanks,Tuan
---In EnergyPlus_Support@xxxxxxxxxxxxxxx, <jcrossett@...> wrote:Also one side of the building is longer then the other, so it is not really fully symmetrical.Possibly I do not understand your question- could you try to explain it again? It is known that different building orientation will cause higher or lower cooling and heating loads..
Jeremiah D. Crossett | Senior Analyst | Phase Change Energy Solutions
On Sun, Nov 17, 2013 at 11:21 PM, <tranhuuanhtuan2004@...> wrote:
Hi Feremiah,I don't understand what you meant. For specific angle, if two models share the same building geometry's description should get the same solar gains, wind-driven heat diffusion... and if they also fully share the same settings and are acting under the same environmental conditions, the heating loads and cooling loads shouldn't change.The Case2 idf files actually are from the model oriented to 180. I tested with either a random angle or 180, they still show the difference.The Case1 idf files are the simple model (a rectangular box with hip roof), its windows are slightly off, so it is not symmetrical. But I just rearranged those windows to make it perfectly symmetrical which I haven't uploaded in here, the problem is still the same.Tuan
---In EnergyPlus_Support@xxxxxxxxxxxxxxx, <jcrossett@...> wrote:Tuan,
The aspect ratio of your model is different. One could only expect that orientation would not matter if it was the case that the building was perfectly symmetrical, your model is not. With this model I guess it would produce exactly the same results if you change 0 for 180, or 90 for 270, but would get different results for any non-full rotation.This is because rotation of your building will be afflicted by solar gains from the south and west (northern hemisphere), and wind speed coefficients for the stronger north wind driving infiltration. Basically, your results make sense and your models are fine.
Jeremiah D. Crossett | Senior Analyst | Phase Change Energy Solutions
On Sun, Nov 17, 2013 at 9:32 PM, <tranhuuanhtuan2004@...> wrote:
Hi Oscar,The problem here is two models are theoretically identical. The difference is how their building geometry are described in relationship with the north axis. So, I think the cooling loads and heating loads should be the same.I even tested with another building type (simpler geometry) and still got the same problem.I attached the idf files if anyone would like to test it out.Here is the Dropbox link of those idf files:https://www.dropbox.com/s/gy2swm1oons749n/IDF%20Files.zip
I included two cases: Case1 (Case1A.idf and Case1B.idf) and Case2 (Case2A.idf and Case2B.idf)
Thank you,Tuan
---In EnergyPlus_Support@xxxxxxxxxxxxxxx, <eng.ohw@...> wrote:
Hi Tuan,2% for heating and cooling maybe it's OK. Changing the north axis you must modify heating loads and on the same time cooling loads. It's difficult to explain without the building description. Try to look at the heating and cooling separate for both models.OscarOn Nov 17, 2013 8:45 PM, <tranhuuanhtuan2004@...> wrote:Hello,I did some parametric testing building orientation with E+. I tested two identical models which are duplicated from the same model and then rotated the first one by changing the North Axis parameter for certain degree in the idf file and the other one I actually changed the building orientation (using DIVA for Grasshopper) for the same angle. I did double check their geometry by importing them into OpenStudio and they are perfectly matched. I run both idf files with the same weather data file and the same version of E+.
However, I got quite off results. Both Heating and Cooling Energy results from the two models are around 2% different. Is there any round-off error issue with E+ or any thought? Thanks.Tuan
--
Tuan Tran, D.Arch, LEED Green AssociatePostdoctoral Fellow,Office of Physical, Environmental and Long Range Planning, University of Hawai'i at ManoaEmail: trantuan@...Phone: (808)206-3635
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