RE: Re: Re: [EnergyPlus_Support] Issue of building orientation in E+

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.

---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

120 E. Pritchard St. | Asheboro, NC 27203

| Mobile 503-688-8951
www.phasechange.com

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.

Oscar

On 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 Associate
Postdoctoral Fellow,
Office of Physical, Environmental and Long Range Planning, University of Hawai'i at Manoa
Email: trantuan@...

Phone: (808)206-3635