Re: [EnergyPlus_Support] Shading in EnergyPlus -- Correction

[Rick Strand <rkstrand@xxxxxxxx>]

Linda:

Sorry--I wasn't paying all that much attention to support email last week 
while I was out of town and too many pile up after a certain number of days 
to go through them all.  I'm glad to see the correction posted.  The roof 
should only shade in the direction of its outward normal so overhangs 
should be used to get the true shading effect.  I hadn't considered the 
thermal mass effect of the excess roof overhang--I'm not sure how much that 
would be.  However, by overspecifying the area of a roof a user could 
artificially increase the amount of heat transfer through the roof because 
E+ will not try to figure out the portion of the roof actually connected to 
the inside.  The roof portion that overhangs is in reality a fin that would 
have some conduction heat transfer impact--if we modeled 2-d effects in 
E+.  I think the biggest impact is still the shading impact and I agree 
that putting an overhang in is essential for modeling this effect.

Rick


At 01:39 PM 8/11/2005, you wrote:
>on 8/4/2005, Question was:
>  >I also have a very simple question concerning roof overhangs: will
>  >they shade windows in the zone below them or not? i.e. do they need
>  >to be modelled as shading surfaces? or they will be automatically
>  >considered in the calculation?
>  >
>
>And I said:
>"Yes, the excess roof geometry will shade windows (and walls) of the
>other zones as appropriate.  There is no need to make them shading
>devices as well."
>
>This is incorrect.  In order to have the excess part of a roof shade
>the walls below it, you must put in overhangs/attached shading
>devices (or detached) to model that part of the building.  Note that
>the excess roof model portion may still be needed for the increased
>thermal mass but it WILL NOT shade the walls below it.
>
>I apologize for my mis-information.
>
>Linda
>
>EnergyPlus WebSite: http://www.energyplus.gov
>Owner: EnergyPlus_Support list
>Member: EnergyPlus Development Team
>
>
>
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