[EnergyPlus_Support] Re: relative/worldcoordinatesystem

["zl21e <zl21e@xxxxxxxxx>" <zl21e@xxxxxxxxx>]

Mike,
Thank you for your explanation.  BTW, if I download the new version 
of e+, do I need to delete the old one first?

Thanks again!

Li

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Michael J. Witte" 
<mjwitte@g...> wrote:
> Li:  See answers below.  Mike
> 
> 
> On 4 Mar 2003, at 5:24, zl21e zl21e@y... 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
> > 
> 
> 
> ========================================================
> EnergyPlus Testing and Support      
> EnergyPlus-Support@g...


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