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Re: [EnergyPlus_Support] Re: wall and roof color
Where can I input the "Thermal Emittance"?
I only find the " Absortance: thermal", " Absorptence: solar" and " Absortance: visible".
What is the resonable value fo these if I select the light and dark color?
Thanks.
Zhen
chillarrahul <chillarrahul@xxxxxxxxx> wrote:
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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