Re: [EnergyPlus_Support] Precise surfaces modelling

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

My apologies for the slow response.

My general advice to users with very thick surfaces is to use the center-line 
dimension so that the total thermal mass and the area used for 1-d heat 
transfer are correct.

a)  Even though surfaces do not have thickness for shading calculations, window 
reveals (or setback) create an implied thickness which will shade the window.  
If you describe the window in a different plane than the base surface, the 
reveal will be accounted for.  See Input Output Reference (v2.2) p.192 (pdf p. 
233).

b)  I do not understand what you mean by "masks" and "non-thermal zone".  
Please give me more description of this.

c)  EnergyPlus does not require that corresponding interzone surfaces are 
geometrially touching.  The interzone heat transfer connection is made using a 
temperature boundary condition, so the two surfaces could theoretically be 
miles (or kilometers) apart without causing any problem in the heat transfer 
modeling.  It's not clear to me that this separation is important, but you may 
certainly describe the surfaces that way if you choose to.

Mike


On 16 Apr 2008 at 15:02, serge.gosset wrote:

> Hi everybody,
> 
> I am trying to figure the best way to model old building surfaces
> (meaning an impressive thickness, especially when we add a comfortable
> insulation layer).  I have been browsing the documentation and the
> Yahoo group, but some issues are still unclear to me.
> 
> Let's summarize:
> 1.- wall thickness is used only for heat transfer and thermal capacitance
> 2.- wall surfaces are used only to determine the zone air volume as
> well as the lighting masks and radiation part of the heat problem.
> 
> Hence a few questions arise:
> a) What happens with narrow windows in thick walls: there is an
> obvious solar mask caused by the wall that is not modelled with
> zero-thickness surfaces?  Should we model only the internal surface
> and add non-thermal masks on the outside to simulate the window
> opening sides ?
> 
> b) Or should we model the outside surface only ?  Have you any idea on
> which is the more thermally accurate ?  Masks should be massless
> inside the thermal zone in this case, or should we put them in a
> non-thermal zone also ?
> 
> c) For inside walls between zones, both surfaces are hit by radiative
> power.  To have a precise modelling of this, we should use both
> surfaces in their exact position, but we can model only a
> zero-thickness surface in E+.  Right ?  Or can we define two different
> surfaces separated by 5o cm and tell E+ that they are both sides of
> the same heat transfer surface.  Can we do this or something similar
> and, if yes, how ?  Can it be automated some way (like in Ecotect, for
> example, in which a tolerance is given below which surfaces are
> considered being both sides of the same wall/partition) ?
> 
> Any suggestion or best practice here ?  This would be an interesting
> topic for many users, I guess ...
> 
> Thanks for your reply & best regards to all
> 
> Serge
> 
> 
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> 



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