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Re: [EnergyPlus_Support] Absorptance

The data in the BLAST and DOE-2 materials libraries are based on 
tables in the ASHRAE Handbook of Fundamentals for all properties 
(except possibly the solar absorptance data).

Regarding thermal emissivities, the 2001 ASHRAE Handbook of 
Fundamentals, Chapter 25, Table 2 lists thermal (IR) emittance values:

Building materials: wood, paper, masonry, nonmetallic paints: 0.90

This is most likely where the 0.9 values in the datasets come from.  
This same table also lists values ranging from 0.05 to 0.7 for 
various metals, and 0.84 for glass.  The windowglass dataset uses 
0.84 for many of the glass types.

Regarding solar absorptance, there appears to be a good variation 
within the materials dataset with 0.65 for concrete block, 0.76 for 
brick, 0.82 for clay tile, 0.2 for steel siding, 0.93 for face brick. 
 I do not know the source of this data.  Certainly similar materials 
with different colors will have different solar and visible 
absorptance.  In "Solar Engineering of Thermal Processes" (Duffie and 
Beckmann, 1980), acrylic white paint is listed as 0.26, but exterior 
building surfaces get dirty and the absorptance can increase 

Perhaps some other users can cite a good data source for these 


On 20 Mar 2003, at 18:23, Alexander Beisteiner wrote:

> Dear E+ User
> By definition, solar absorptance defines the shortwave absorptance of
> a material. This value differs between materials and colours: a black
> surface represents a value of one. As in the Blast and DOE material
> libraries almost all entries show quite high values, except for metal,
> I assume surface colours are meant to be rather dark. Although IR
> emittance changes with material and colour- and so must IR
> absorptance, all entries in the material library show values of 0.9
> for IR absorptance. Is there a reason for such a definition. Further,
> general material data bases only specify the solar absorptance
> properties but not the thermal ones. What is the data source for the
> Blast and DOE materials found in the E+ DataSet folder?
> Alexander
> _______________________________________ 
> DI (FH) Alexander Beisteiner
> Wissenschaftlicher Mitarbeiter
> Forschungs- und Technologietransfer Pinkafeld GmbH
> Steinamangerstraße 21 
> A - 7423 Pinkafeld
> Tel.: +43-3357-45370 DW 1324
> Fax.: +433357-45370 DW 1010

EnergyPlus Testing and Support      

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