Knowledgebase : Shading/Daylighting
Question:
When the simulation runs it results in some warnings about shadow overlap:

"** Warning ** Too many figures [>=15000] in a shadow overlap
** ~~~ ** Overlapping figure=518CC3, Surface Class=[Detached Shading:Building]
** ~~~ ** This error occurred 1 times.
** ~~~ ** Figure being Overlapped=AA74A3, Surface Class=[Detached Shading:Building]"

I understand this situation but I don't know if affects the results. If so, what should I do? erase the building that shadows other shadow? thank you
Answer:
You have three options for dealing with this warning:

1. You can use the ShadowCalculation object to specify a higher limit for "Maximum Figures in Shadow Overlap Calculations" (v6.0 Input Output Reference, pdf p. 63).

2. All shading surfaces are mirrored by default, resulting in twice as many shading surfaces. This is done so the user does not have to be careful about the facing direction of a shading surface. This feature can be disabled using the Output:Diagnostics object with the DoNotMirrorDetachedShading option. (v6.0 Input Output Reference, pdf p. 64). With this option, you must be careful to face shading surfaces toward the building so that shadows will be cast properly. Shading:Zone:Detailed surfaces are always mirrored, even with this option, so it may be useful to reclassify some shading surfaces as this type.

3. If may be safe to ignore these warnings, but it is hard to know for sure. Output:variable "Surface Ext Sunlit Fraction" can be used to verify is shadows are being cast as expected.

Mike



Ricardo Gomes Posted on: 31 Jan 2011 09:51 AM
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Ok, thank you.



Michael J. Witte, GARD Analytics, Inc.

Q: I am trying to model a daylighting system, but I am not seeing an effect on the electric power consumption. I have moved my reference points to locations where they will see the variation in daylight. I have also run the file with the electric lighting dimming control "continuous" (1). But I still don't observe any change in the lighting electric power consumption. I am not able to figure out the exact problem. Is there some other connection between lighting control and lighting electric consumption that I am not aware of?

A: One of the problems is somewhat subtle. In the LIGHTS input object, Fraction Replaceable must be set to 1.0 in order for electric light dimming due to daylight to take effect. This is documented in the I/O reference, and also a warning is generated in the ERR file. However, this is not always
obvious to users. Check that the Fraction Replaceable is set to 1.0.