Trans material - single pane of polycarbonate

radiance-general
1

HI!

I am trying to model a panel of polycarbonate (modeled as a surface facing
the sun).

My goal is to determine the annual solar radiation behind it.

Since I have the following values:

- Transmission 71%

- Haze 66%

I am trying to model the polycarbonate as a "trans" material in Radiance.

Then, I perform the radiation analysis (I use DIVA4RHINO and Daysim model)
with the following parameters for the trans material:

void trans polycarbonate

0

0

7 0.972 0.902 0.835 0.07 0 0.706 0.344

But. I obtain very low radiation values (from 30% to 50% of radiation loss).

Does this loss seem unreal as a result?

Do you think that "trans" material is the right choice for the
polycarbonate?

Any suggestion?

Thank you in advance

Erika

2

Hi Erika,

I believe that the "trans" material is a reasonable start for this panel as far as you have described it.

Your material will come out a little low on transmission, since the transmitted fraction of 0.706 multiplied by the color (0.9 or so) comes out to 64% transmission rather than your target of 71%. This does not explain why your values are so low, but it may have to do with your sampling parameters. Diffuse scattering from your trans surface implies that an additional "ambient bounce" is needed to account for this light. Did you try increasing your -ab parameter?

Best,
-Greg

···

From: "Erika Saretta" <[email protected]>
Date: March 25, 2017 1:43:06 AM PDT

HI!

I am trying to model a panel of polycarbonate (modeled as a surface facing the sun).
My goal is to determine the annual solar radiation behind it.

Since I have the following values:
- Transmission 71%
- Haze 66%
I am trying to model the polycarbonate as a “trans” material in Radiance.

Then, I perform the radiation analysis (I use DIVA4RHINO and Daysim model) with the following parameters for the trans material:

void trans polycarbonate
0
0
7 0.972 0.902 0.835 0.07 0 0.706 0.344

But… I obtain very low radiation values (from 30% to 50% of radiation loss).
Does this loss seem unreal as a result?
Do you think that “trans” material is the right choice for the polycarbonate?

Any suggestion?

Thank you in advance

Erika

3

Erika,
Have you seen a sample of the material? I see you note a Haze value of 66%, which is somewhat telling but not directly transferrable into a radiance definition. Is the material almost completely translucent with almost no specular transmission, or is it partially clear that you can see objects through it? Your trans parameter #7 (you have 0.344) I think implies that the material is transmitting roughly one-third of its transmission as direct and non-diffused transmission (direct view through the material).

I don't think that comment would solve your transmission loss problem, but would be worth a test rendering to see if the light transmission directionality "looks" the way you'd expect.

-Chris

···

From: Erika Saretta [mailto:[email protected]]
Sent: Saturday, March 25, 2017 4:43 AM
To: [email protected]
Subject: [Radiance-general] Trans material - single pane of polycarbonate

HI!

I am trying to model a panel of polycarbonate (modeled as a surface facing the sun).
My goal is to determine the annual solar radiation behind it.

Since I have the following values:

- Transmission 71%

- Haze 66%
I am trying to model the polycarbonate as a "trans" material in Radiance.

Then, I perform the radiation analysis (I use DIVA4RHINO and Daysim model) with the following parameters for the trans material:

void trans polycarbonate
0
0
7 0.972 0.902 0.835 0.07 0 0.706 0.344

But... I obtain very low radiation values (from 30% to 50% of radiation loss).
Does this loss seem unreal as a result?
Do you think that "trans" material is the right choice for the polycarbonate?

Any suggestion?

Thank you in advance

Erika

____________________________________________________________
Electronic mail messages entering and leaving Arup business
systems are scanned for acceptability of content and viruses

4

Wouldn't simple model (based on simple haze value) for Radiance be a BSDF
with specular (diagonal) portion being 34% and lambertian portion (uniform
diffuse in all directions 66%)? For this specific sample Tdiff =
0.4686, Tspec = 0.2414. Calculation done using logic below (H=Haze as a
fraction).

        Tdiff = H*Ttot
        Adding other fundamentals
        Ttot = Tdiff + Tspec
        Tspec = Ttot-Tdiff = (1-H)*Ttot

Charlie

···

On Thu, Mar 30, 2017 at 12:09 PM, Christopher Rush < [email protected]> wrote:

Erika,

Have you seen a sample of the material? I see you note a Haze value of
66%, which is somewhat telling but not directly transferrable into a
radiance definition. Is the material almost completely translucent with
almost no specular transmission, or is it partially clear that you can see
objects through it? Your trans parameter #7 (you have 0.344) I think
implies that the material is transmitting roughly one-third of its
transmission as direct and non-diffused transmission (direct view through
the material).

I don’t think that comment would solve your transmission loss problem, but
would be worth a test rendering to see if the light transmission
directionality “looks” the way you’d expect.

-Chris

*From:* Erika Saretta [mailto:[email protected]]
*Sent:* Saturday, March 25, 2017 4:43 AM
*To:* [email protected]
*Subject:* [Radiance-general] Trans material - single pane of
polycarbonate

HI!

I am trying to model a panel of polycarbonate (modeled as a surface facing
the sun).

My goal is to determine the annual solar radiation behind it.

Since I have the following values:

- Transmission 71%

- Haze 66%

I am trying to model the polycarbonate as a “trans” material in Radiance.

Then, I perform the radiation analysis (I use DIVA4RHINO and Daysim model)
with the following parameters for the trans material:

void trans polycarbonate

0

0

7 0.972 0.902 0.835 0.07 0 0.706 0.344

But… I obtain very low radiation values (from 30% to 50% of radiation
loss).

Does this loss seem unreal as a result?

Do you think that “trans” material is the right choice for the
polycarbonate?

Any suggestion?

Thank you in advance

Erika

____________________________________________________________
Electronic mail messages entering and leaving Arup business
systems are scanned for acceptability of content and viruses

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

--

*--------------------------------------------------------------------------*

*D. Charlie Curcija**, Ph.D. ** Tel: (510) 495-2602*

*Lawrence Berkeley National Laboratory Fax: (510) 486-4089*

*Windows & Envelope Materials Group Cell:(510) 604-8668*

*1 Cyclotron Rd., MS 90-3111 Email: [email protected]
<[email protected]>*

*Berkeley, CA 94720 Web: http://windows.lbl.gov/
<http://btech.lbl.gov/>*

*--------------------------------------------------------------------------*

5

Hi Charlie,
I think you might be right in theory, but I’ve never been convinced that Haze Factor is particularly accurate based on various haze factor values I’ve seen on product data sheets (but I can’t recall specific examples to substantiate that, so I might be projecting unnecessary skepticism). I would be quite happy to be informed of its reliability by someone with greater familiarity with the ASTM standard.

I’m thinking of it the same way that EN testing for woven shade fabrics gives more accurate results than the ASTM testing. I think a Tv(n-n) value from EN testing would give you a more accurate idea of specular transmission than the Haze Factor from ASTM D-1003. There might be different degrees of rigor dictated by the two different testing standards (required measurement angles, etc.), or the calculation methods prescribed to translate that measured data to a single % value.

I’m not an expert on either standard, but in any case I think checking expected results v. simulated results is a good idea.

-Chris

···

From: D. Charlie Curcija [mailto:[email protected]]
Sent: Thursday, March 30, 2017 5:04 PM
To: Radiance general discussion
Subject: Re: [Radiance-general] Trans material - single pane of polycarbonate

Wouldn't simple model (based on simple haze value) for Radiance be a BSDF with specular (diagonal) portion being 34% and lambertian portion (uniform diffuse in all directions 66%)? For this specific sample Tdiff = 0.4686, Tspec = 0.2414. Calculation done using logic below (H=Haze as a fraction).

        Tdiff = H*Ttot
        Adding other fundamentals
        Ttot = Tdiff + Tspec
        Tspec = Ttot-Tdiff = (1-H)*Ttot

Charlie

On Thu, Mar 30, 2017 at 12:09 PM, Christopher Rush <[email protected]<mailto:[email protected]>> wrote:
Erika,
Have you seen a sample of the material? I see you note a Haze value of 66%, which is somewhat telling but not directly transferrable into a radiance definition. Is the material almost completely translucent with almost no specular transmission, or is it partially clear that you can see objects through it? Your trans parameter #7 (you have 0.344) I think implies that the material is transmitting roughly one-third of its transmission as direct and non-diffused transmission (direct view through the material).

I don’t think that comment would solve your transmission loss problem, but would be worth a test rendering to see if the light transmission directionality “looks” the way you’d expect.

-Chris

From: Erika Saretta [mailto:[email protected]<mailto:[email protected]>]
Sent: Saturday, March 25, 2017 4:43 AM
To: [email protected]<mailto:[email protected]>
Subject: [Radiance-general] Trans material - single pane of polycarbonate

HI!

I am trying to model a panel of polycarbonate (modeled as a surface facing the sun).
My goal is to determine the annual solar radiation behind it.

Since I have the following values:

- Transmission 71%

- Haze 66%
I am trying to model the polycarbonate as a “trans” material in Radiance.

Then, I perform the radiation analysis (I use DIVA4RHINO and Daysim model) with the following parameters for the trans material:

void trans polycarbonate
0
0
7 0.972 0.902 0.835 0.07 0 0.706 0.344

But… I obtain very low radiation values (from 30% to 50% of radiation loss).
Does this loss seem unreal as a result?
Do you think that “trans” material is the right choice for the polycarbonate?

Any suggestion?

Thank you in advance

Erika
____________________________________________________________
Electronic mail messages entering and leaving Arup business
systems are scanned for acceptability of content and viruses

6

Christopher,

I think that you bring some interesting points, but I am afraid that you
are mixing few things here. Lets try to untangle it a bit:

- Haze measurement is simplified measurement, but for relatively thin
samples it is reasonably accurate. It does not give you directional
accuracy, nor spectral info, but overall specular vs. scattering split is
pretty good.
- Thick scattering samples are difficult to measure accurately, period.
Haze meter or not. My colleague here at LBNL is working through NFRC and
ICG TC10 to establish criteria how to properly do it. As it turns out large
integrating sphere or full goniophotometer is required to correctly measure
thick samples. Potentially, a correlation could be developed that would
allow measurement using smaller integrating sphere, but that is yet to be
found.
- Fabrics measurement according to EN standard - I am presuming that you
have in mind spectral measurement using ISO 9050 (or EN equivalent). If
not, let me know what EN measurement method you have in mind. One general
observation, though. Fabrics are thin scattering products, so their
measurement is not questionable. EN does not offer any advantage to what we
have developed through the new AERC organization, which will be published
as series of standards later this year.

To summarize, thick scattering samples need to be measured using large
integrating sphere, so neither haze meter nor Spectrophotometer with 150 mm
sphere is adequate. Thin scattering samples, fabrics included can
reasonably be measured with haze meter and Spectrophotometer with 150 mm
sphere, with the provision that haze meter does not give you any spectral
level information or directional resolution, just split between specular
and scattering.

Charlie

···

On Fri, Mar 31, 2017 at 7:11 AM, Christopher Rush <[email protected] > wrote:

Hi Charlie,

I think you might be right in theory, but I’ve never been convinced that
Haze Factor is particularly accurate based on various haze factor values
I’ve seen on product data sheets (but I can’t recall specific examples to
substantiate that, so I might be projecting unnecessary skepticism). I
would be quite happy to be informed of its reliability by someone with
greater familiarity with the ASTM standard.

I’m thinking of it the same way that EN testing for woven shade fabrics
gives more accurate results than the ASTM testing. I think a Tv(n-n) value
from EN testing would give you a more accurate idea of specular
transmission than the Haze Factor from ASTM D-1003. There might be
different degrees of rigor dictated by the two different testing standards
(required measurement angles, etc.), or the calculation methods prescribed
to translate that measured data to a single % value.

I’m not an expert on either standard, but in any case I think checking
expected results v. simulated results is a good idea.

-Chris

*From:* D. Charlie Curcija [mailto:[email protected]]
*Sent:* Thursday, March 30, 2017 5:04 PM
*To:* Radiance general discussion
*Subject:* Re: [Radiance-general] Trans material - single pane of
polycarbonate

Wouldn't simple model (based on simple haze value) for Radiance be a BSDF
with specular (diagonal) portion being 34% and lambertian portion (uniform
diffuse in all directions 66%)? For this specific sample Tdiff =
0.4686, Tspec = 0.2414. Calculation done using logic below (H=Haze as a
fraction).

        Tdiff = H*Ttot

        Adding other fundamentals

        Ttot = Tdiff + Tspec

        Tspec = Ttot-Tdiff = (1-H)*Ttot

Charlie

On Thu, Mar 30, 2017 at 12:09 PM, Christopher Rush < > [email protected]> wrote:

Erika,

Have you seen a sample of the material? I see you note a Haze value of
66%, which is somewhat telling but not directly transferrable into a
radiance definition. Is the material almost completely translucent with
almost no specular transmission, or is it partially clear that you can see
objects through it? Your trans parameter #7 (you have 0.344) I think
implies that the material is transmitting roughly one-third of its
transmission as direct and non-diffused transmission (direct view through
the material).

I don’t think that comment would solve your transmission loss problem, but
would be worth a test rendering to see if the light transmission
directionality “looks” the way you’d expect.

-Chris

*From:* Erika Saretta [mailto:[email protected]]
*Sent:* Saturday, March 25, 2017 4:43 AM
*To:* [email protected]
*Subject:* [Radiance-general] Trans material - single pane of
polycarbonate

HI!

I am trying to model a panel of polycarbonate (modeled as a surface facing
the sun).

My goal is to determine the annual solar radiation behind it.

Since I have the following values:

- Transmission 71%

- Haze 66%

I am trying to model the polycarbonate as a “trans” material in Radiance.

Then, I perform the radiation analysis (I use DIVA4RHINO and Daysim model)
with the following parameters for the trans material:

void trans polycarbonate

0

0

7 0.972 0.902 0.835 0.07 0 0.706 0.344

But… I obtain very low radiation values (from 30% to 50% of radiation
loss).

Does this loss seem unreal as a result?

Do you think that “trans” material is the right choice for the
polycarbonate?

Any suggestion?

Thank you in advance

Erika

____________________________________________________________
Electronic mail messages entering and leaving Arup business
systems are scanned for acceptability of content and viruses

_______________________________________________
Radiance-general mailing list
[email protected]
http://www.radiance-online.org/mailman/listinfo/radiance-general

--

*--------------------------------------------------------------------------*

*D. Charlie Curcija**, Ph.D. ** Tel: (510) 495-2602*

*Lawrence Berkeley National Laboratory Fax: (510) 486-4089*

*Windows & Envelope Materials Group Cell:(510) 604-8668*

*1 Cyclotron Rd., MS 90-3111 Email: [email protected]
<[email protected]>*

*Berkeley, CA 94720 Web: http://windows.lbl.gov/
<http://btech.lbl.gov/>*

*--------------------------------------------------------------------------*

7

Hi Charlie,
Thanks for the note of confidence in haze factor. I guess if I see a third-party lab ASTM D1003 report for a material, I might consider it for developing an approximate a radiance material definition.

At what thickness do you think haze factor (if reported) might not be reliable for a radiance definition? 5mm acrylic? 10mm laminated glass with diffusing interlayer? Multi-pane IGU maybe 30mm with diffusion applied to on one or more faces or interlayers?

My ASTM / EN comparison with fabric testing was not related to spectral data, but visible transmittance values given according to EN14501 with Tv,n-n & Tv,n-h (maybe the ASTM equivalent is E903 which I believe might be less accurate). Apologies I didn’t think to include those in my previous message, and may have been misleading since not directly related to glazing.

Thanks,
Chris

···

From: D. Charlie Curcija [mailto:[email protected]]
Sent: Tuesday, April 04, 2017 2:38 PM
To: Radiance general discussion
Subject: Re: [Radiance-general] Trans material - single pane of polycarbonate

Christopher,

I think that you bring some interesting points, but I am afraid that you are mixing few things here. Lets try to untangle it a bit:

- Haze measurement is simplified measurement, but for relatively thin samples it is reasonably accurate. It does not give you directional accuracy, nor spectral info, but overall specular vs. scattering split is pretty good.
- Thick scattering samples are difficult to measure accurately, period. Haze meter or not. My colleague here at LBNL is working through NFRC and ICG TC10 to establish criteria how to properly do it. As it turns out large integrating sphere or full goniophotometer is required to correctly measure thick samples. Potentially, a correlation could be developed that would allow measurement using smaller integrating sphere, but that is yet to be found.
- Fabrics measurement according to EN standard - I am presuming that you have in mind spectral measurement using ISO 9050 (or EN equivalent). If not, let me know what EN measurement method you have in mind. One general observation, though. Fabrics are thin scattering products, so their measurement is not questionable. EN does not offer any advantage to what we have developed through the new AERC organization, which will be published as series of standards later this year.

To summarize, thick scattering samples need to be measured using large integrating sphere, so neither haze meter nor Spectrophotometer with 150 mm sphere is adequate. Thin scattering samples, fabrics included can reasonably be measured with haze meter and Spectrophotometer with 150 mm sphere, with the provision that haze meter does not give you any spectral level information or directional resolution, just split between specular and scattering.

Charlie

On Fri, Mar 31, 2017 at 7:11 AM, Christopher Rush <[email protected]<mailto:[email protected]>> wrote:
Hi Charlie,
I think you might be right in theory, but I’ve never been convinced that Haze Factor is particularly accurate based on various haze factor values I’ve seen on product data sheets (but I can’t recall specific examples to substantiate that, so I might be projecting unnecessary skepticism). I would be quite happy to be informed of its reliability by someone with greater familiarity with the ASTM standard.

I’m thinking of it the same way that EN testing for woven shade fabrics gives more accurate results than the ASTM testing. I think a Tv(n-n) value from EN testing would give you a more accurate idea of specular transmission than the Haze Factor from ASTM D-1003. There might be different degrees of rigor dictated by the two different testing standards (required measurement angles, etc.), or the calculation methods prescribed to translate that measured data to a single % value.

I’m not an expert on either standard, but in any case I think checking expected results v. simulated results is a good idea.

-Chris

From: D. Charlie Curcija [mailto:[email protected]<mailto:[email protected]>]
Sent: Thursday, March 30, 2017 5:04 PM
To: Radiance general discussion
Subject: Re: [Radiance-general] Trans material - single pane of polycarbonate

Wouldn't simple model (based on simple haze value) for Radiance be a BSDF with specular (diagonal) portion being 34% and lambertian portion (uniform diffuse in all directions 66%)? For this specific sample Tdiff = 0.4686, Tspec = 0.2414. Calculation done using logic below (H=Haze as a fraction).

        Tdiff = H*Ttot
        Adding other fundamentals
        Ttot = Tdiff + Tspec
        Tspec = Ttot-Tdiff = (1-H)*Ttot

Charlie

On Thu, Mar 30, 2017 at 12:09 PM, Christopher Rush <[email protected]<mailto:[email protected]>> wrote:
Erika,
Have you seen a sample of the material? I see you note a Haze value of 66%, which is somewhat telling but not directly transferrable into a radiance definition. Is the material almost completely translucent with almost no specular transmission, or is it partially clear that you can see objects through it? Your trans parameter #7 (you have 0.344) I think implies that the material is transmitting roughly one-third of its transmission as direct and non-diffused transmission (direct view through the material).

I don’t think that comment would solve your transmission loss problem, but would be worth a test rendering to see if the light transmission directionality “looks” the way you’d expect.

-Chris

From: Erika Saretta [mailto:[email protected]<mailto:[email protected]>]
Sent: Saturday, March 25, 2017 4:43 AM
To: [email protected]<mailto:[email protected]>
Subject: [Radiance-general] Trans material - single pane of polycarbonate

HI!

I am trying to model a panel of polycarbonate (modeled as a surface facing the sun).
My goal is to determine the annual solar radiation behind it.

Since I have the following values:

- Transmission 71%

- Haze 66%
I am trying to model the polycarbonate as a “trans” material in Radiance.

Then, I perform the radiation analysis (I use DIVA4RHINO and Daysim model) with the following parameters for the trans material:

void trans polycarbonate
0
0
7 0.972 0.902 0.835 0.07 0 0.706 0.344

But… I obtain very low radiation values (from 30% to 50% of radiation loss).
Does this loss seem unreal as a result?
Do you think that “trans” material is the right choice for the polycarbonate?

Any suggestion?

Thank you in advance

Erika

____________________________________________________________
Electronic mail messages entering and leaving Arup business
systems are scanned for acceptability of content and viruses

_______________________________________________
Radiance-general mailing list
[email protected]<mailto:[email protected]>
http://www.radiance-online.org/mailman/listinfo/radiance-general

--

--------------------------------------------------------------------------

D. Charlie Curcija, Ph.D. Tel: (510) 495-2602

Lawrence Berkeley National Laboratory Fax: (510) 486-4089

Windows & Envelope Materials Group Cell:(510) 604-8668

1 Cyclotron Rd., MS 90-3111 Email: [email protected]<mailto:[email protected]>

Berkeley, CA 94720 Web: http://windows.lbl.gov/<http://btech.lbl.gov/>

--------------------------------------------------------------------------