[esp-r] Re: rules for surfaces to be shaded (correctly) in ESP-r

[Jon Hand (clcv10)]

ESRU hints....

Several users have recently created models which look geometrically
correct but which the shading and insolation analysis is not correct.

There have been a few messages in the past about the relationship
between zone surfaces and obstruction blocks to avoid the dreaded
crossing-the-plane mesaage.

The engine in the ish module is ALSO sensitive to the edge ordering
of surfaces and the direction of the first two edges of surfaces. This
is legacy code and no one has found the time to update it.

The interface does not currently look at the polygons as they are  
created and
revise them to conform to the foibles of ish. Generating models that  
work
is thus an issue for users and for the people charged with model QA.

The rule set seems to be:

a) Ish figures out the orientation of a surface by looking at the first
     3 vertices of the surface (other modules uses a different
     technique).

b) ish works best if the initial edge of the surface is close to  
horizontal
    and the 2nd edge is at an angle to the first edge (i.e. two edges  
along
    the same line can fail).

c) ish seems to get the orientation wrong if the first edge of the  
surface
    is a vector pointing down.

d) for flat surfaces orientation is not particularly an issue

e) just because the wire-frame image looks correct the surface might
     just be facing backwards - if you are in the northern hemisphere  
and
     it is noon and direct solar radiation is coming in a window that is
     supposed to be on the north you probably have a reversed surface

For surfaces which have no edge which is close to horizontal and which
you notice is causing trouble - add a short (~25-50mm) near-horizontal
edge at the start of the surface.

How do you figure out if shading and insolation are working correctly?

a) use the wireframe view-from-the-sun FIRST to get an impression
     of the solar exposure of the model at different times of the year
    as well as looking at where sunlight would go in rooms. Actually
    this is a technique experts employ as they are creating models in
    order to decide if solar access is an issue.

b) turn on the synopsis in the ish module as the shading calculations
    progresses

c) use the view surface shading option in the ish module to review the
     pattern of shading on surfaces of interest

d) use the solar-entering and solar absorbed reports/graphs in the
     results analysis

-ESRU