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[EnergyPlus_Support] Re: wall and roof color



If you want your walls to be black then
0.9000000 , !- Thermal Emittance
0.9500000 , !- Solar Absorptance

if you walls are white then
0.9000000 , !- Thermal Emittance
0.2600000 , !- Solar Absorptance
the values vary and you could look up them from any heat 
transfer book. The values i have written are at 30Deg C.




--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Rahul Chillar 
<chillarrahul@y...> wrote:
> hello
> Regarding your first question, Color does have an effect but COLOR 
can be varied by changing the Emittance , absorptance of the material 
> For Example: If you want your walls to be black then
>   0.9000000    ,   !- Thermal Emittance
>   0.9500000    ,   !- Solar Absorptance
>  
> These values are function of color  of material.  
> another example:
> if you walls are white then
>   0.9000000    ,   !- Thermal Emittance
>   0.2600000    ,   !- Solar Absorptance
> the values vary and you could look up them from any heat transfer 
book. The values i have written are at 30Deg C.
>  
> Again if you wall is made of say asphalt then the E+ material 
values will have the correct values of these fields to take into 
account the effect of color of asphalt.
>  
>  So i can is that the software E+ is taking care of it, however 
feel free to cross check the values from any data book. The values 
vary with temperature, roughness which will be very difficult to 
quantize. 
>  
> Regarding 2: a possbile reason for deviation from what you expect 
could be that in the materials you mentioned CONCRETE - 3/4 IN 
MORTAR, CEMENT SA 3 / 4 IN, A1 - 1 IN STUCCO 
> 
> These values will very with color or your concrete/ material which 
may be a little darker, or lighter basically vary from place to place 
so you may feel these are not satisfing your requirements. Then again 
the Roughness of the materials are different .
> 
>  
> 
> Hope this helps
> 
> Thanks
> 
> Rahul Chillar
> 
> Building Systems lab
> 
> Graduate Research Assistant
> 
> Univ of Illinois Urbana Champaign
> 
> 
> teklay Weldeabzgi <teklay1979@y...> wrote:
> 
> hello ever body i need some help on these questions
> 1. how does E+ considers the effect of wall and roof
> color in cooling load. i know that color has a
> considerable effect on cooling load of a building but
> i can't understand how to take this effect in E+.
> 
> 2. i have some doubt with material properties given in
> the dataset of E+. especially on the thermal
> emittance, solar Absorptance, and Solar Absorptance.
> for example if u see the following three materials i
> think they sould have the same property but it differs
> greatly. 
> 
>      MATERIAL:Regular,CONCRETE - 3/4 IN MORTAR,  !-
> Material Name
> Rough,  !- Roughness
>   1.0000000E-02,  !- Thickness {m}
>   0.7200000    ,   !- Conductivity {w/m-K}
>    1858.140    ,   !- Density {kg/m3}
>    830.0000    ,   !- Specific Heat {J/kg-K}
>   0.9000000    ,   !- Thermal Emittance
>   0.2000000    ,   !- Solar Absorptance
>   0.2000000    ;   !- Visible Absorptance
> 
>   MATERIAL:Regular,PLASTER - CEMENT SA 3 / 4 IN,  !-
> Material Name
> Smooth,  !- Roughness
>   9.9999998E-03,  !- Thickness {m}
>   0.7200000    ,   !- Conductivity {w/m-K}
>    1858.140    ,   !- Density {kg/m3}
>    830.0000    ,   !- Specific Heat {J/kg-K}
>   0.9000000    ,   !- Thermal Emittance
>   0.7800000    ,   !- Solar Absorptance
>   0.7800000    ;   !- Visible Absorptance
> 
> MATERIAL:Regular,A1 - 1 IN STUCCO,  !- Material Name
> Smooth,  !- Roughness
>   2.0000000E-02,  !- Thickness {m}
>   0.6900000    ,   !- Conductivity {w/m-K}
>    1858.140    ,   !- Density {kg/m3}
>    830.0000    ,   !- Specific Heat {J/kg-K}
>   0.9000000    ,   !- Thermal Emittance
>   0.9200000    ,   !- Solar Absorptance
>   0.9200000    ;   !- Visible Absorptance
> 
>   MATERIAL:Regular,CONCRETE - 3 / 4 IN STUCCO,  !-    
>                                    Material Name
> VeryRough,  !- Roughness
>   9.9999998E-03,  !- Thickness {m}
>   0.7100000    ,   !- Conductivity {w/m-K}
>    1874.160    ,   !- Density {kg/m3}
>    830.0000    ,   !- Specific Heat {J/kg-K}
>   0.9000000    ,   !- Thermal Emittance
>   0.7200000    ,   !- Solar Absorptance
>   0.7200000    ;   !- Visible Absorptance
> 
> why is this happen ?  if these properties are not the
> exact value can u help me how to get the exact value.
> you can imagin that these properties varies the
> cooling load greatly.
> 
> tahnks
> tek
> 
> 
> 
>             
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> Thanks 
> Rahul Chillar 
> Grad Student 
> Building Systems lab
> Univ Of Illinois Urbana Champaign
> 
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