[Radiance-general] Representation of a solar sceen in radiance

[Greg Ward]

Hi Per,

The Radiance "BRTDfunc" material offers the most control over these parameters, and can be done with a single surface.  The "glaze" script can get you pretty close to what you want by simulating your system as a single-pane fritted glazing.  I generated the following using a 95% coverage (corresponding roughly to a 4% visibility factor):

% glaze
###
### NOTE: Using internal demo database!
###

Enter the number of panes in the system: 1

Window normal faces interior

  | |
  | |
  | |
  | |-->
  | |
  | |
  | |
 s1 s2

Supported surface types are:
   1 - clear glass
   2 - VE1-2M low-E coating
   3 - PVB laminated
   4 - V-175 white frit
   5 - V-933 warm gray frit

What is the type of s1? 5
What is the type of s2? 1
Enter fraction coverage for s1 (0-1): .95

############################################
# Glazing produced by Radiance glaze script
# $Revision: 2.8 $
# Material surface normal points to interior
# Number of panes in system: 1
# Exterior surface s1 type: V-933 warm gray frit
# s1 coating coverage: .95
# Interior surface s2 type: clear glass
# Exterior normal hemispherical reflectance: 0.20331675
# Interior normal hemispherical reflectance: 0.14631675
# Normal hemispherical transmittance: 0.129616
#
void BRTDfunc glaze1_unnamed
10
	sr_frit_r sr_frit_g sr_frit_b
	st_frit_r st_frit_g st_frit_b
	0 0 0
	glaze1.cal
0
11
0.0722
0.06935
0.06745
0.1995
0.1995
0.1995
0.0855
0.0855
0.0855
	1	.95

--------
Based on the output above, the gray frit I used (V-933) is not dark enough to simulate your system, since the tranmission is about twice too high (0.129616 instead of 0.06).  This is mostly in the diffuse transmitted part, so you can probably adjust the 0.0855 values above to something like 0.02 (three times) to get close to your 6% total transmission.  I have no idea what the diffuse reflection values should be, since you didn't give us those measurements.

Cheers,
-Greg

> From: Christopher Rush <Christopher.Rush at arup.com>
> Date: January 4, 2017 6:40:14 AM PST
> 
> If you use the “glass” material type, you would get varying reflection/transmission at certain angles based on Snell’s law, refractive index, critical angle, etc. – on both sides of the glass, which might not be representative of your system. You could consider one surface/layer to represent the glass (“glass” material type might be good enough approximation) and another layer to represent the screen (maybe “trans” material type unless you want to specify angular-dependent properties). If you want to combine the effect of glass with screen into one surface/layer then you probably need to consider something more complex if the different reflective properties on each side of the system are important. There are also more accurate ways to model glass if it has specific coatings, etc. that are important to the results.
>  
> -Chris
>  
>  
> From: Per Haugaard [mailto:perhaugaard at yahoo.dk] 
> Sent: Wednesday, January 04, 2017 4:26 AM
> To: Radiance Radiance
> Subject: [Radiance-general] Representation of a solar sceen in radiance
>  
> Dear users,
>  
> Happy New Year. 
> I am looking for the best way to represent a gray semi transparent solar screen in radiance. Would it be to represent is as a sheet of glass with the total light transmissions or?
> The screen is placed on the exterior side of the window and has a solartransmission of 6%, light transmission of 6% and an openness factor of 4%.The colour rendering index is 100.
> The total light transmissions of the screen and glass is 4%.
>  
> Any input is appreciated.
>  
> Best regards
> Per Haugaard
>  
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