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[EnergyPlus_Support] RE: Shading of many overhangs and calculation time
Hi,
Thanks for your answers. I've been investigating this question a bit further and here are my current conclusions:
1. My assumption that a Shading:Overhang object only shades the fenestration it's attached to was wrong. E+ will find all the receiving surfaces in the model for a given overhang. A look at the Surface Shadowing Summary report shows that clearly.
2. However, a detached shading object such as Shading:Building:Detailed will be automatically mirrored by E+. Which means that for overhangs at least, that adds unnecessary shading calculations. This behaviour can be disabled with the following statement: OutputDiagnostics, DoNotMirrorDetachedShading; To be used wisely!
So there is a slight advantage (in terms of calculation time; I'm ignoring other considerations for the sake of this argument) in using Shading:Overhang above Shading:Building:Detailed for modelling a rectangular overhang.
I'm still working on this tower with lots of overhangs. Because each overhang has a lot of shadow receiving surfaces, I'm getting loads of the following warnings (or at least I think that's the reason):
** Warning ** Too many figures [>=100000] in a shadow overlap
** ~~~ ** Overlapping figure=Mir-SUB SURFACE 28-40-14 OVERHANG, Surface Class=[Shading]
** ~~~ ** This error occurred 2 times.
** ~~~ ** Figure being Overlapped=SURFACE 16-27-581, Surface Class=[Wall]
** ~~~ ** Figure being Overlapped=SURFACE 16-27-17049, Surface Class=[Wall]
Am I just supposed to ignore these in this case, as hinted here:
http://energyplus.helpserve.com/Knowledgebase/Article/View/70/17/too-many-figures-in-a-shadow-overlap
Cheers,
Patrick
---In energyplus_support@xxxxxxxxxxxxxxx, <o.hans@...> wrote:
@Jeremiah
Shading:Overhang is not necessarily symmetrical. The projection from the window corner can be input for each side individually.
> ---In EnergyPlus_Support@xxxxxxxxxxxxxxx, <jeannieboef@...> wrote:
>
> ------->With shading overhang you have the benefit of a symmetrical model where you could add all your shading in a ratio based method so it would be a global setting- might want to do so on a orientation basis.. Also shading detailed may involve many surfaces, the primary issue with long runtime. I am not so familar with shading building. Also you might consider use of controlled blinds.
>
>
> Jeremiah D. Crossett | Senior Analyst | Phase Change Energy Solutions
120 E. Pritchard St. | Asheboro, NC 27203 | Mobile 503-688-8951
<http://www.phasechange.com>www.phasechange.com
<http://i.imgur.com/Sldxf.jpg>
>
>
>
>
>> On Thu, Nov 14, 2013 at 11:02 PM, Patrick Bivona <<mailto:patrick.bivona@...>patrick.bivona@...> wrote:
>>>
Hello,
>>> I'm working on a high-rise tower block. I'd like to model balcony overhangs that provide shading to the glazing below.
>>> There are 3 objects I can think of using:
1. Shading:Building
2. Shading:Zone:Detailed
3. Shading:Overhang
>>>
>>> Knowing that I have about 500 balcony overhangs, I'm wondering if there are significant differences in terms of calculation time between these 3 options.
>>> My thinking is that a Shading:Overhang object is only shading the glazing it's attached to. Whereas, for the 2 other options, E+ has to calculate the effect of each shading surface on all the other building surfaces in view.
>>> Does it make that much difference?
>>> Many thanks,
Patrick
>>>
>>>
>>
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