Re: [EnergyPlus_Support] relative/worldcoordinatesystem

["Michael J. Witte" <mjwitte@xxxxxxxx>]

Li:  See answers below.  Mike


On 4 Mar 2003, at 5:24, zl21e zl21e@xxxxxxxxx wrote:

> Hello, Everyone,
> I have some questions about the relative/worldcoordinatesystem.
> 
> For relative coordinate system, each zone origin coordinates are
> specified relative to the buiding origin (which is 0,0,0).  Every
> surface vertice's coordinates in that zone are relative to the zone
> origin coordinates.  For world coordinate system, all zone origin
> coordinates are (0,0,0). Every vertice's coordinates are absolute
> coordinates to (0,0,0). Is that right?

Yes, that is correct.  In addition, with relative coordinates, the 
building north axis field becomes active.

> 
> In the sample file s1r3DD.idf, relative coordinate system is used. 
> However, all zone origin coordinates are (0,0,0). Every vertice's
> coordinates are absolute coordinates to (0,0,0). Is it the same as
> world coordinate system?

It is almost the same.  With relative coordinates, the building north 
axis could be applied.  With world coordinates, it cannot.  (By the 
way, s1r3DD is quite old, you may need to upgrade versions.)

> 
> In the sample file VAVSingleDuctReheat.idf, world coordinate system is
> used.  However,  each zone origin coordinates are specified relative
> to the buiding origin (which is 0,0,0). Every vertice's coordinates
> are still absolute coordinates to (0,0,0). Why does this happen?
> 

When daylighting is used, the coordinates for the daylighting 
reference points are always relative to the zone origin.  If using 
world coordinates, the zone origins may be left at (0,0,0) and then 
the daylighting reference points would effectively be in world 
coordinates.  Or, the surfaces could be in world coordinates with non-
zero zone origins, as in this example.  In this case, daylighting 
reference points would be in relative coordinates.  In this 
particular example, daylighting is not used, so there is no real 
reason for non-zero zone origins, but it does not affect the results. 
 (Not all of our examples represent the best practice.)


> Thank you!
> 
> Sincerely,
> Li Zhang
> Department of Mechanical Engineering
> Iowa State University
> Ames, IA 50010
> 


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