[EnergyPlus_Support] Building Overhangs

["yijun huang" <yijunhuang@xxxxxxxxxxx>]

Dear Mike and Edward,

Thanks for the advice. My model is similar to the 3rd sketch by Mike, and I 
have so far been describing the model as Mike has suggested, a rood surface 
until the external wall, and an external shading surface that does not 
transfer heat to the interior zone.

However, since my roof construction (for a tropical climate) is of 
substantial thermal mass, I was concerned with the horizontal heat flow in 
the roof (with large overhangs) that might affect the interior zone.

Edward has suggested seperate 2D thermal modelling for the roof (using 
THERM) to circumvent the problem, and I was wondering if there are any 
similar strategies that I can use in E+? (Since I don't have support in 
using THERM)

Also, what is the difference between the 3 mentioned types of detached 
shading surfaces?

Thanks guys!

Cheers
HUANG Yi Chun
Research Assistant
Department of Architecture
National University of Singapore






>From: "Michael J. Witte" <mjwitte@xxxxxxxx>
>Reply-To: EnergyPlus_Support@xxxxxxxxxxxxxxx
>To: EnergyPlus_Support@xxxxxxxxxxxxxxx
>Subject: Re: [EnergyPlus_Support] Building Overhangs
>Date: Mon, 24 Feb 2003 15:08:11 -0600
>
>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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