Re: [EnergyPlus_Support] Building Overhangs

["Michael J. Witte" <mjwitte@xxxxxxxx>]

Would you please provide a sketch of the overhang you are modeling?  
If you are modeling an attic space and the overhang transfers heat 
to/from the attic, then you can describe the overhang surfaces as 
heat transfer surfaces with the proper orientations and the shading 
will be modeled as desired.  Perhaps these two examples will help 
(use fixed space font to see this picture correctly).

Example 1 (overhang transfers heat to the attic):

       /
      /    Attic
     /
    /____ _______________
         !
         !    Interior Zone
         !
         !

In this example, the attic floor would be two surfaces, one over the 
interior space, and then an exterior surface (facing downward) for 
the overhang.  The full roof area should be modeled, because it 
transfers heat to the attic.


Example 2 (overhand does not transfer heat to attic):

            /
           /    Attic
          /
         /________________
        /!
       / !    Interior Zone
      /  !
         !
         !

In this example, the attic floor would be one surface over the 
interior space.  The attic roof would be one surface extending only 
to the exterior wall.  The overhang would be a shading surface, 
because it does not transfer heat to the attic or the interior.

Example 3 (no attic):

            /
           /    
          /
         /
        /!
       / !    Interior Zone
      /  !
         !
         !

In this example, roof would be one surface extending only to the 
exterior wall.  The overhang would be a shading surface, because it 
does not transfer heat to the interior.

Mike



On 24 Feb 2003, at 18:25, sdep1017 yijunhuang@xxxxxxxxxxx wrote:

> Hi, I am using E+ 1.0.2 and attempting to model a simple building with
> an overhanging roof construction that casts shadows on all external
> walls.
> 
> According to the documentation, specifying and oversized roof will not
> work in considering the shading effects, that the overhangs should be
> modelled as surface:shading:detached (since the overhang casts shadows
> on more than 1 surface).
> 
> My 2 questions are:
> 
> 1. How do I account for the thermal makeup of the overhanging 
> portions of the roof since defining it as a surface:shading in E+ does
> not do so? (The roof I'm modelling consists of several layers)
> 
> 2. What is the difference between Surface:Shading:Detached, 
> Surface:Shading:Detached:Fixed and Surface:Shading:Detached:Building?
> From the documentation it seems they are the same?
> 
> Thank you.
> 
> Cheers,
> HUANG Yi Chun
> Research Assistant
> Department of Architecture
> National University of Singapore
> 
> 
> 
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