[Radiance-general] Representation of a solar sceen in radiance
Gregory J. Ward
gregoryjward at gmail.com
Sat Jan 7 07:35:57 PST 2017
Hi Per,
I am re-editing your subject line again. Please, when responding to the mailing list especially, make sure that your subject line stays consistent for searches, and it is best *not* to include the entire digest, as it often contains different threads (though not in this case). The instructions regarding the subject line are repeated below, so no excuses.
Unfortunately, I cannot glean much useful information based on the material composition. I'm not a material scientist, but presumably they could put any number of dyes and pigments in their PVC/fiberglass mix. If the exterior reflectance is 76%, however, I would expect the interior reflectance to be similar unless there is something unusual about the construction. The glass will reduce this slightly (88% squared), so it is probably reasonable to set the interior diffuse reflectance to something like 0.66 for the first three values:
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 0.66 0.66 0.66 0.78 0.78 0.78 0.02 0.02 0.02 1 .95
The above is a reasonable guess, I believe.
Cheers,
-Greg
> From: Per Haugaard <perhaugaard at yahoo.dk>
> Subject: Re: [Radiance-general] Radiance-general Digest, Vol 155, Issue 3
> Date: January 7, 2017 12:27:12 AM PST
>
> Hi Greg,
>
> Thank you for your reply. It is much helpful.
> The data sheet holds no information on the interior reflection so no help there. The material composition is 64% PVC & 36% fibreglass if that is of any help based on you experience.
>
>
> Best regards
>
> Per Haugaard
>
>
> Den 19:12 fredag den 6. januar 2017 skrev "radiance-general-request at radiance-online.org" <radiance-general-request at radiance-online.org>:
>
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> 1. Re: Representation of a solar sceen in radiance (Gregory J. Ward)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Fri, 6 Jan 2017 10:10:34 -0800
> From: "Gregory J. Ward" <gregoryjward at gmail.com>
> To: Radiance general discussion <radiance-general at radiance-online.org>
> Cc: Per Haugaard <perhaugaard at yahoo.dk>
> Subject: Re: [Radiance-general] Representation of a solar sceen in
> radiance
> Message-ID: <8C4C55DC-CD34-46B7-96C9-CAA7ED252F4E at gmail.com>
> Content-Type: text/plain; charset="us-ascii"
>
> HI Per,
>
> I changed the subject back to the original, but I see that you sent this reply to me alone.
>
> The BRTDfunc type is a material in Radiance, so it should modify a surface directly, not another material. Therefore, you should apply your "glaze1_unnamed" material directly to the polygon of your window.
>
> Your changes to the arguments are as I suggested to get the desired total transmission. If light reflection is 76% and our frit coverage is 95%, that means that the "back side" diffuse reflection should be much higher -- around 78% or so. I would suggest changing the specification as follows:
>
> 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 0.78 0.78 0.78 0.02 0.02 0.02 1 .95
>
> The actual reflection on the exterior of the building will matter more to outside views than inside views and illumination. Do they give any information about interior reflection for the shading system? This would affect what we specify for the first three arguments.
>
> Cheers,
> -Greg
>
> > From: Per Haugaard <perhaugaard at yahoo.dk>
> > Date: January 6, 2017 5:03:53 AM PST
> >
> > Hi Greg,
> >
> > Thank you for your answer.
> > The data sheet does not say anything about the diffuse reflection but the solar reflection is listed to 77% and the light reflection is listed to 76%. Can this lead us to a more precise description?.
> >
> > I am not familiar with the BRTDfunc or glaze script but it looks interesting. Would the description in the material file be:
> >
> > 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 0.02 0.02 0.02 1 .95
> >
> > glaze1_unnamed glass clear_glass_with_screen
> > 0
> > 0
> > 3 0.06 0.06 0.06
> >
> > What should the specular reflection and specular transmission be in the description of the material?
> >
> > I would much appreciate if you could help me or point me in the direction of better understanding the BRTDfunc and how to use it.
> >
> >
> > Best regards
> >
> > Per Haugaard
> >
> >
> > Date: Wed, 4 Jan 2017 14:21:44 -0800
> > From: Greg Ward <gregoryjward at gmail.com>
> >
> >
> > 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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