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Re: [EnergyPlus_Support] wall and roof color
Hello,
regarding to this subject, I have one doubt:
Does E+ consider same value for Thermal Emittance than
for Thermal Absortance?
I say this, because in the idf editor, the fields you
find for a material:regular or material:regular-r
objects are the following (for radiative properties):
MATERIAL:REGULAR-R,
, !- Name
, !- Roughness
, !- Thermal Resistance {m2-K/W}
0.9, !- Absorptance:Thermal
0.7, !- Absorptance:Solar
0.7; !- Absorptance:Visible
If this is not a mistake, how could I set the value
for emittance and emissivity of an opaque material?
For glass materials there is a field for the IR
Emissivity, but I cannot find how to introduce it for
an opaque wall material.
Thanks,
Carmen.
--- Rahul Chillar <chillarrahul@xxxxxxxxx> escribió:
---------------------------------
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@xxxxxxxxx> 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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