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North axis in openstudio app and E+

asked 2020-08-16 17:51:12 -0500

antonszilasi's avatar

updated 2020-08-17 14:40:49 -0500

I want to clarify the functionality of the north axis under the building section in the OpenStudio app and E+.

Does this field simply rotate the building relative to true north (green arrow) or does it change true north (and therefore the sun position)?

From the documentation I understand its the former but I want to be sure. Thank you!

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Good question! I wonder if there is a difference between the two?

Ski90Moo's avatar Ski90Moo  ( 2020-08-17 08:38:15 -0500 )edit

I have noticed that the Geometry tab of the OSApp will draw an orange line representing the value of 'North Axis' input field, but also will rotate the displayed geometry relative to the green axis by the same amount. In contrast, the same model loaded in the Sketchup Plugin (at least prior to v3.0) will draw the modified north axis in orange, but leave the geometry unchanged relative to the drawing coordinate system. IMO the way the app does it adds confusion.

Eric Ringold's avatar Eric Ringold  ( 2020-08-17 13:32:58 -0500 )edit

@Eric Ringold I agree that it adds confusion hence the question Ive asked here

antonszilasi's avatar antonszilasi  ( 2020-08-17 14:10:02 -0500 )edit

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answered 2021-01-08 13:58:49 -0500

antonszilasi's avatar

updated 2021-01-08 15:46:21 -0500

Hi all,

As a note in the end I used the dxf export to solve this once and for all it shows the north axis.

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answered 2020-08-17 10:27:57 -0500

updated 2020-08-17 10:28:48 -0500

The North Axis input field for the Building of EnergyPlus or OpenStudio models rotates the building's north axis to be relative to true north (green line in your screen shot). Positive values rotate the building clockwise from true north.

Note that this input is ONLY used if theGlobalGeometryRules object uses "Relative" coordinate systems. If you are using "World" coordinate systems (or the alternative "Absolute" option available in EnergyPlus versions 9.2 and earlier), then you will need to rotate the building geometry directly.

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One other point about rotation, is that site:shading objects are not impacted by this, so when choosing between site and building shading, when you plan to have non-zero rotation, be careful. If you are doing a parametric study of building rotation with static site context, you may want to use site shading vs. building. In that case the origin of the of the model is also important, would probably want near center of building instead of corner.

David Goldwasser's avatar David Goldwasser  ( 2020-08-17 10:57:02 -0500 )edit

@Aaron Boranian thank you for detailed your reply, to clarify in the case of using relative coordinates does that mean the the green axis will always be "true north" aka the sun position? Im still not clear on this.

antonszilasi's avatar antonszilasi  ( 2020-08-17 14:09:13 -0500 )edit

Good point on the shading impacts as well, @David Goldwasser. @antonszilasi yes, the green axis will always be "true north" -- the direction that the north pole of a compass would point. The "building's north axis" is just a drawing convention to make line/point snapping for horizontal or vertical lines easier than having to constantly draw angled lines that match the real site's orientation.

Aaron Boranian's avatar Aaron Boranian  ( 2020-08-17 14:20:42 -0500 )edit

thank you @Aaron Boranian!

antonszilasi's avatar antonszilasi  ( 2020-08-17 15:54:58 -0500 )edit

Actually, in OpenStudio the orange line is true North, green is Building Y-axis.

macumber's avatar macumber  ( 2020-08-18 08:51:58 -0500 )edit

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Asked: 2020-08-16 17:51:12 -0500

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Last updated: Jan 08 '21