Re: [EnergyPlus_Support] Cool surface

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

I am not sure I understand completely what you mean by "cool surfaces."  Do you 
mean light-colored exterior surfaces intended to reduce cooling load by 
reflecting a higher fraction of the incident solar?  If yes, then 
absorptance:solar is the primary influence.  This governs how much of the 
incident solar radiation is absorbed by the surface.  Absorptance:thermal is 
also important, because it governs the long-wave radiant transfer between the 
surface and the sky and ground (if it is not a horizontal surface).  The 
visible absorptance is used for the visible fraction of energy output from 
LIGHTS and for daylighting calculations.  For exterior surfaces, remember that 
it is the value of the outermost MATERIAL in the CONSTRUCTION list that governs 
heat transfer on the outside surface.  

And as Tasos suggested, you may find more details in the Engineering Reference.

Mike


On 13 Dec 2007 at 13:18, Michela wrote:

> I'm trying to simulate cool surfaces, the first question whether is 
> it possible to simulate in E+ or not?
> If yes, the parameters which affect the performance are Absorptance 
> :Thermal, Absorptance: Solar and Absorptance: Visible, defined under 
> Group Surface construction elements.
> 
> I try to change these parameters and observed that among these, the 
> parameter Absorptance: Solar affects strongly the performance in 
> comparison to other two parameters (Thermal and Visible). Somebody 
> can tell me how E+ calculates the surface emissivity because it is 
> important in case of cool surfaces.
> 
> Thanks a lot.
> 
> Michela
> 
> 
> 
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> 
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> 
> 
> 
> 
> 


========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support      
EnergyPlus-Support@xxxxxxxx





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