Asking for informations

[VS-A.jpg]

VS-A

architectes d.p.l.g / ingénierie de l'enveloppe

Hi Radiance team,

I am a student in an engineering school and I am currently doing an internship in a design office specialized in building envelope studies.

My work consist in developing a tool to determine precisely the solar factor of a facade, taking into account its shading devices and its geometry which can be complex sometimes.

My idea is to use the software Grasshopper to:

1. Import a geometry

2. Define the materials of the scene

3. Create the Radiance geometry

4. Create two analysis grid (vertical): one before the system "shading+facade" to determine the incident solar energy, and one inside my building to determine the transmitted solar energy.

5. Then, use the Ray Tracing method to calculate the solar energy on each point...
This method seems interesting for my problematic but the calculations under the hood may be not relevant for solar energy, insofar as it is designed for light calculations and realistic rendering.

Questions :

1) I apology if I am missing something obvious, I have done some researches about the "Ray tracing" method used by Radiance but I still have some interrogations about how it works... Is the ray divided in many rays when it punch a surface ? What is the different between the direct light and the diffuse light (in terms of modeling) ? Is there a way to convert R G B radiance provided by Radiance in solar energy for instance (like it is done for luminance) ?

2) I must not be the first to process this kind of problematic, so I am wondering if it exists a calculation engine derived from Radiance which can provide the solar energy using a kind of "ray tracing" method?

For me, in principle, it is not that complicated, I mean it is possible. The problematic is purely geometric and mathematic. I imagine: the ray launched is define by a wave length, an intensity and a direction (to model the direct radiation). When it reaches a surface, the intensity took into account is the intensity of the surface's normal projection of the ray. Then the ray is divided in 3 rays: one transmitted, one reflected and one absorbed, whose proportions (in terms of intensity) and directions depend on the material definition of the surface reached. This last can react differently according to wavelength domain of the ray. Do the same with diffuse rays, to model the diffuse radiation. The absorbed part of the incident energy could be transformed in heat (Infrared radiation) according to the emissivity of the surface.

I am sorry about the lenth of the message. I really need to understand how I can do to determine solar energy through different kind of materials (translucent, transparent, opaque...). I would be really thankful if you help me! This project constitute my graduation project, it is quite ambitious that's why I need some guidelines.

Thank you in advance,
Yours sincerely

Severine Huet

VS-A, architectes d.p.l.g / ingénierie de l'enveloppe

41 place Rihour / F-59000 LILLE - France
Tél : +33 (0)3.20.52.11.44 ; Ligne directe : +33 (0)3.20.52.xx.xx / Fax : +33 (0)3.20.52.05.15
email : courrier@vs-a.eu<mailto:courrier@vs-a.eu> / email direct : S.HUET@vs-a.eu<mailto:S.HUET@vs-a.eu> / www.vs-a.eu

Ce courriel (et ses pièces jointes) est adressé exclusivement à son destinataire ; il n'a pas de valeur hors de ce contexte précis et peut être confidentiel. Nous remercions d'avance les destinataires involontaires de s'abstenir de le dupliquer de quelque manière que ce soit, et de le détruire. Merci également de bien vouloir en avertir l'expéditeur.

This e-mail (and its attachments) is intended to be for the only use of its recipient; the message is worthless out of this specific context and may contain confidential information. If you have received this e-mail by mistake, please do not duplicate it in any possible way. Thank you as well for notifying us immediately and deleting this e-mail.

Dear Séverine,

Radiance is not really best suited. Typically, what you describe is covered
by thermal building simulation tools to a quite high degree of detail
(ESP-r, EnergyPlus, IDA-ICE, TRNSYS to name a few). It would likely be quite
difficult or probably even impossible e.g. to model the secondary heat gain
through windows / glazed facades (or opaque facades, for that matter). Also,
“what goes through” is not the whole story. What happens in the building is
also of major interest to be able to decide if the gains are “useful” or
“harmful”.

Why do you think you need the ray tracing approach?

Best

Achim

···

from my point of view, if your interest lies with solar >energy< gain, then

Von: Séverine HUET [mailto:S.HUET@vs-a.eu]
Gesendet: Mittwoch, 6. April 2016 15:35
An: radiance-general@radiance-online.org
Betreff: [Radiance-general] Asking for informations

VS-A.jpg

VS-A

architectes d.p.l.g / ingénierie de l’enveloppe

Hi Radiance team,

I am a student in an engineering school and I am currently doing an
internship in a design office specialized in building envelope studies.

My work consist in developing a tool to determine precisely the solar factor
of a facade, taking into account its shading devices and its geometry which
can be complex sometimes.

My idea is to use the software Grasshopper to:

1. Import a geometry

2. Define the materials of the scene

3. Create the Radiance geometry

4. Create two analysis grid (vertical): one before the system
“shading+facade” to determine the incident solar energy, and one inside my
building to determine the transmitted solar energy.

5. Then, use the Ray Tracing method to calculate the solar energy on each
point

This method seems interesting for my problematic but the calculations under
the hood may be not relevant for solar energy, insofar as it is designed for
light calculations and realistic rendering.

Questions :

1) I apology if I am missing something obvious, I have done some
researches about the “Ray tracing” method used by Radiance but I still have
some interrogations about how it works
Is the ray divided in many rays when
it punch a surface ? What is the different between the direct light and the
diffuse light (in terms of modeling) ? Is there a way to convert R G B
radiance provided by Radiance in solar energy for instance (like it is done
for luminance) ?

2) I must not be the first to process this kind of problematic, so I am
wondering if it exists a calculation engine derived from Radiance which can
provide the solar energy using a kind of “ray tracing” method?

For me, in principle, it is not that complicated, I mean it is possible. The
problematic is purely geometric and mathematic. I imagine: the ray launched
is define by a wave length, an intensity and a direction (to model the
direct radiation). When it reaches a surface, the intensity took into
account is the intensity of the surface’s normal projection of the ray. Then
the ray is divided in 3 rays: one transmitted, one reflected and one
absorbed, whose proportions (in terms of intensity) and directions depend on
the material definition of the surface reached. This last can react
differently according to wavelength domain of the ray. Do the same with
diffuse rays, to model the diffuse radiation. The absorbed part of the
incident energy could be transformed in heat (Infrared radiation) according
to the emissivity of the surface.

I am sorry about the lenth of the message. I really need to understand how I
can do to determine solar energy through different kind of materials
(translucent, transparent, opaque
). I would be really thankful if you help
me! This project constitute my graduation project, it is quite ambitious
that’s why I need some guidelines.

Thank you in advance,

Yours sincerely

Severine Huet

VS-A, architectes d.p.l.g / ingénierie de l’enveloppe

41 place Rihour / F-59000 LILLE – France

Tél : +33 (0)3.20.52.11.44 ; Ligne directe : +33 (0)3.20.52.xx.xx / Fax :
+33 (0)3.20.52.05.15

email : <mailto:courrier@vs-a.eu> courrier@vs-a.eu / email direct :
<mailto:S.HUET@vs-a.eu> S.HUET@vs-a.eu / <http://www.vs-a.eu> www.vs-a.eu

Ce courriel (et ses pièces jointes) est adressé exclusivement à son
destinataire ; il n’a pas de valeur hors de ce contexte précis et peut être
confidentiel. Nous remercions d’avance les destinataires involontaires de
s’abstenir de le dupliquer de quelque manière que ce soit, et de le
détruire. Merci également de bien vouloir en avertir l’expéditeur.

This e-mail (and its attachments) is intended to be for the only use of its
recipient; the message is worthless out of this specific context and may
contain confidential information. If you have received this e-mail by
mistake, please do not duplicate it in any possible way. Thank you as well
for notifying us immediately and deleting this e-mail.

Hi Séverine,

I often use Radiance for performing calculations in the solar range. In
that case, I just use grey surfaces (R=G=B=solar reflectance), and ask the
Perez sky models to give me solar instead of visible Radiance (I think this
is done using O1 option in the command line).

It is important to notice that these methods will not consider convection
and far infrared radiation, thus the absorbed-reemited heat will not be
considered.

On the other hand, depending on the geometry of your facade system, it
might be worth calculating the BSDF (using genBSDF). Then, the BSDF may be
imported to Window for estimating solar heat gain coefficient, considering
convection and FIR radiation.

If you want to avoid Window, the method used by it to calculate absorption
on each layer is very well documented y two papers by J.H.Klems. Then,
ISO15099 will give you a hint on how to calculate the solar heat gain
coefficient from all the information you have at that point.

Those three components would allow you, respectively, to:

1. Calculate transmission and reflection of each layer (genbsdf)
2. Calculate absorption on each layer (Klems)
3. Calculate the inward flowing fraction of the absorbed radiation
(iso15099)

Yes... Avoiding windows is hard.

Best,

···

El 7 abr. 2016 03:23, "Achim Geissler" <achim.geissler@intergga.ch> escribió:

Dear Séverine,

from my point of view, if your interest lies with solar >energy< gain,
then Radiance is not really best suited. Typically, what you describe is
covered by thermal building simulation tools to a quite high degree of
detail (ESP-r, EnergyPlus, IDA-ICE, TRNSYS to name a few). It would likely
be quite difficult or probably even impossible e.g. to model the secondary
heat gain through windows / glazed facades (or opaque facades, for that
matter). Also, “what goes through” is not the whole story. What happens in
the building is also of major interest to be able to decide if the gains
are “useful” or “harmful”.

Why do you think you need the ray tracing approach?

Best

Achim

*Von:* Séverine HUET [mailto:S.HUET@vs-a.eu]
*Gesendet:* Mittwoch, 6. April 2016 15:35
*An:* radiance-general@radiance-online.org
*Betreff:* [Radiance-general] Asking for informations

[image: VS-A.jpg]

*VS-A*

architectes d.p.l.g / ingénierie de l’enveloppe

Hi Radiance team,

I am a student in an engineering school and I am currently doing an
internship in a design office specialized in building envelope studies.

My work consist in developing a tool to determine precisely the solar
factor of a facade, taking into account its shading devices and its
geometry which can be complex sometimes.

My idea is to use the software Grasshopper to:

1. Import a geometry

2. Define the materials of the scene

3. Create the Radiance geometry

4. Create two analysis grid (vertical): one before the system
“shading+facade” to determine the incident solar energy, and one inside my
building to determine the transmitted solar energy.

5. Then, use the Ray Tracing method to calculate the solar energy on
each point…

This method seems interesting for my problematic but the calculations
under the hood may be not relevant for solar energy, insofar as it is
designed for light calculations and realistic rendering.

Questions :

1) I apology if I am missing something obvious, I have done some
researches about the “Ray tracing” method used by Radiance but I still have
some interrogations about how it works… Is the ray divided in many rays
when it punch a surface ? What is the different between the direct light
and the diffuse light (in terms of modeling) ? Is there a way to convert R
G B radiance provided by Radiance in solar energy for instance (like it is
done for luminance) ?

2) I must not be the first to process this kind of problematic, so I
am wondering if it exists a calculation engine derived from Radiance which
can provide the solar energy using a kind of “ray tracing” method?

For me, in principle, it is not that complicated, I mean it is possible.
The problematic is purely geometric and mathematic. I imagine: the ray
launched is define by a wave length, an intensity and a direction (to model
the direct radiation). When it reaches a surface, the intensity took into
account is the intensity of the surface’s normal projection of the ray.
Then the ray is divided in 3 rays: one transmitted, one reflected and one
absorbed, whose proportions (in terms of intensity) and directions depend
on the material definition of the surface reached. This last can react
differently according to wavelength domain of the ray. Do the same with
diffuse rays, to model the diffuse radiation. The absorbed part of the
incident energy could be transformed in heat (Infrared radiation) according
to the emissivity of the surface.

I am sorry about the lenth of the message. I really need to understand how
I can do to determine solar energy through different kind of materials
(translucent, transparent, opaque…). I would be really thankful if you help
me! This project constitute my graduation project, it is quite ambitious
that’s why I need some guidelines.

Thank you in advance,

Yours sincerely

Severine Huet

*VS-A, architectes d.p.l.g / ingénierie de l’enveloppe*

41 place Rihour / F-59000 LILLE – France

Tél : +33 (0)3.20.52.11.44 ; Ligne directe : +33 (0)3.20.52.xx.xx / Fax : +33
(0)3.20.52.05.15

email : courrier@vs-a.eu / email direct : S.HUET@vs-a.eu / www.vs-a.eu

Ce courriel (et ses pièces jointes) est adressé *exclusivement* à son
destinataire ; il n’a pas de valeur hors de ce contexte précis et peut être
confidentiel. Nous remercions d’avance les destinataires involontaires de
s’abstenir de le dupliquer de quelque manière que ce soit, et de le
détruire. Merci également de bien vouloir en avertir l’expéditeur.

This e-mail (and its attachments) is intended to be for the *only* use of
its recipient; the message is worthless out of this specific context and
may contain confidential information. If you have received this e-mail by
mistake, please do not duplicate it in any possible way. Thank you as well
for notifying us immediately and deleting this e-mail.

_______________________________________________
Radiance-general mailing list
Radiance-general@radiance-online.org
http://www.radiance-online.org/mailman/listinfo/radiance-general

Hello Germ�n

/You wrote: I often use Radiance for performing calculations in the solar range. In that case, I just use grey surfaces (R=G=B=solar reflectance), and ask the Perez sky models to give me solar instead of visible Radiance (I think this is done using O1 option in the command line).//
/
Can you configure falsecolor to map as w/sqm?

Regards
*Terrance McMinn*

Yes, there is a -m multiplier option to falsecolor, which defaults to -m 179 and should equate to lux or cd/m². Luminance in cd/m2 is the default label to display luminance unless you give the -l lux option for example for illuminance - both related to the 179 lumen/Watt multiplier.

However for Watts you can use -m 1 in your options to falsecolor along with -l W/m2 to change the label to display as W/m2. That is presuming your image is calculated with -i option for irradiance. I don't think people would normally expect to see a Watts based radiance image in W/sr/m2.

This is also presuming the intent of your image takes into account all the shortcomings that Achim noted.

Can you configure falsecolor to map as w/sqm?

···

From: Terrance McMinn [mailto:t.mcminn@ocpms.com.au]
Sent: Thursday, April 07, 2016 9:39 AM

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

Dear Séverine,

I retract my answer from this morning – not quite awake yet, sorry. Basically, I would support Germán. There is also the tool WIS available, which (also) calculates according to ISO 15099. Depending on the level of detail you are seeking, it may be of interest to look at the Tools “TRISCO/VOLTRA” from Physibel. These would also include thermal transport through framing etc. if you are thinking of curtain walls (lots of metal, often). They are slightly less capable in terms of glass description but geared toward energy.

Anyway, developing a tool which goes beyond the mentioned (in depth of detail and accuracy) is definitely not an easy task … good luck!

Best

Achim

···

Von: Germán Molina Larrain [mailto:germolinal@gmail.com]
Gesendet: Donnerstag, 7. April 2016 13:48
An: Radiance general discussion
Betreff: Re: [Radiance-general] Asking for informations

Hi Séverine,

I often use Radiance for performing calculations in the solar range. In that case, I just use grey surfaces (R=G=B=solar reflectance), and ask the Perez sky models to give me solar instead of visible Radiance (I think this is done using O1 option in the command line).

It is important to notice that these methods will not consider convection and far infrared radiation, thus the absorbed-reemited heat will not be considered.

On the other hand, depending on the geometry of your facade system, it might be worth calculating the BSDF (using genBSDF). Then, the BSDF may be imported to Window for estimating solar heat gain coefficient, considering convection and FIR radiation.

If you want to avoid Window, the method used by it to calculate absorption on each layer is very well documented y two papers by J.H.Klems. Then, ISO15099 will give you a hint on how to calculate the solar heat gain coefficient from all the information you have at that point.

Those three components would allow you, respectively, to:

1. Calculate transmission and reflection of each layer (genbsdf)
2. Calculate absorption on each layer (Klems)
3. Calculate the inward flowing fraction of the absorbed radiation (iso15099)

Yes... Avoiding windows is hard.

Best,

El 7 abr. 2016 03:23, "Achim Geissler" <achim.geissler@intergga.ch> escribió:

Dear Séverine,

from my point of view, if your interest lies with solar >energy< gain, then Radiance is not really best suited. Typically, what you describe is covered by thermal building simulation tools to a quite high degree of detail (ESP-r, EnergyPlus, IDA-ICE, TRNSYS to name a few). It would likely be quite difficult or probably even impossible e.g. to model the secondary heat gain through windows / glazed facades (or opaque facades, for that matter). Also, “what goes through” is not the whole story. What happens in the building is also of major interest to be able to decide if the gains are “useful” or “harmful”.

Why do you think you need the ray tracing approach?

Best

Achim

Von: Séverine HUET [mailto:S.HUET@vs-a.eu]
Gesendet: Mittwoch, 6. April 2016 15:35
An: radiance-general@radiance-online.org
Betreff: [Radiance-general] Asking for informations

VS-A.jpg

VS-A

architectes d.p.l.g / ingénierie de l’enveloppe

Hi Radiance team,

I am a student in an engineering school and I am currently doing an internship in a design office specialized in building envelope studies.

My work consist in developing a tool to determine precisely the solar factor of a facade, taking into account its shading devices and its geometry which can be complex sometimes.

My idea is to use the software Grasshopper to:

1. Import a geometry

2. Define the materials of the scene

3. Create the Radiance geometry

4. Create two analysis grid (vertical): one before the system “shading+facade” to determine the incident solar energy, and one inside my building to determine the transmitted solar energy.

5. Then, use the Ray Tracing method to calculate the solar energy on each point…

This method seems interesting for my problematic but the calculations under the hood may be not relevant for solar energy, insofar as it is designed for light calculations and realistic rendering.

Questions :

1) I apology if I am missing something obvious, I have done some researches about the “Ray tracing” method used by Radiance but I still have some interrogations about how it works… Is the ray divided in many rays when it punch a surface ? What is the different between the direct light and the diffuse light (in terms of modeling) ? Is there a way to convert R G B radiance provided by Radiance in solar energy for instance (like it is done for luminance) ?

2) I must not be the first to process this kind of problematic, so I am wondering if it exists a calculation engine derived from Radiance which can provide the solar energy using a kind of “ray tracing” method?

For me, in principle, it is not that complicated, I mean it is possible. The problematic is purely geometric and mathematic. I imagine: the ray launched is define by a wave length, an intensity and a direction (to model the direct radiation). When it reaches a surface, the intensity took into account is the intensity of the surface’s normal projection of the ray. Then the ray is divided in 3 rays: one transmitted, one reflected and one absorbed, whose proportions (in terms of intensity) and directions depend on the material definition of the surface reached. This last can react differently according to wavelength domain of the ray. Do the same with diffuse rays, to model the diffuse radiation. The absorbed part of the incident energy could be transformed in heat (Infrared radiation) according to the emissivity of the surface.

I am sorry about the lenth of the message. I really need to understand how I can do to determine solar energy through different kind of materials (translucent, transparent, opaque…). I would be really thankful if you help me! This project constitute my graduation project, it is quite ambitious that’s why I need some guidelines.

Thank you in advance,

Yours sincerely

Severine Huet

VS-A, architectes d.p.l.g / ingénierie de l’enveloppe

41 place Rihour / F-59000 LILLE – France

Tél : +33 (0)3.20.52.11.44 <tel:%2B33%20%280%293.20.52.11.44> ; Ligne directe : +33 (0)3.20.52.xx.xx / Fax : +33 (0)3.20.52.05.15 <tel:%2B33%20%280%293.20.52.05.15>

email : <mailto:courrier@vs-a.eu> courrier@vs-a.eu / email direct : <mailto:S.HUET@vs-a.eu> S.HUET@vs-a.eu / <http://www.vs-a.eu> www.vs-a.eu

Ce courriel (et ses pièces jointes) est adressé exclusivement à son destinataire ; il n’a pas de valeur hors de ce contexte précis et peut être confidentiel. Nous remercions d’avance les destinataires involontaires de s’abstenir de le dupliquer de quelque manière que ce soit, et de le détruire. Merci également de bien vouloir en avertir l’expéditeur.

This e-mail (and its attachments) is intended to be for the only use of its recipient; the message is worthless out of this specific context and may contain confidential information. If you have received this e-mail by mistake, please do not duplicate it in any possible way. Thank you as well for notifying us immediately and deleting this e-mail.

_______________________________________________
Radiance-general mailing list
Radiance-general@radiance-online.org
http://www.radiance-online.org/mailman/listinfo/radiance-general

Achim,
I would say your answer is an important one to keep in mind, regarding the limitations of any chosen process and how the information will be used. Is the intent for system peak capacity relying on comprehensive energy accounting? Or only relative performance comparison of shading systems where insulation properties would be similar amongst them all?

I’m not an expert in the software you listed (ESP-r, EnergyPlus, IDA-ICE, TRNSYS, etc.), but I do suspect some or all of them may have limited accuracy in angular dependent complex fenestration. By my guess they might be able to do reasonably well at comprehensive energy modeling of a simple overhang or external light shelf. But if you have a custom designed louver system you may get more accurate direct radiation calculations using Radiance. However if it’s important for your intentions, you would certainly need some other energy modeling tools to consider the bigger picture of heat transfer (insulation, etc.).

-Chris

···

From: Achim Geissler [mailto:achim.geissler@intergga.ch]
Sent: Thursday, April 07, 2016 10:26 AM
To: 'Radiance general discussion'
Subject: Re: [Radiance-general] Asking for informations

Dear Séverine,

I retract my answer from this morning – not quite awake yet, sorry. Basically, I would support Germán. There is also the tool WIS available, which (also) calculates according to ISO 15099. Depending on the level of detail you are seeking, it may be of interest to look at the Tools “TRISCO/VOLTRA” from Physibel. These would also include thermal transport through framing etc. if you are thinking of curtain walls (lots of metal, often). They are slightly less capable in terms of glass description but geared toward energy.

Anyway, developing a tool which goes beyond the mentioned (in depth of detail and accuracy) is definitely not an easy task … good luck!

Best
Achim

Von: Germán Molina Larrain [mailto:germolinal@gmail.com]
Gesendet: Donnerstag, 7. April 2016 13:48
An: Radiance general discussion
Betreff: Re: [Radiance-general] Asking for informations

Hi Séverine,

I often use Radiance for performing calculations in the solar range. In that case, I just use grey surfaces (R=G=B=solar reflectance), and ask the Perez sky models to give me solar instead of visible Radiance (I think this is done using O1 option in the command line).

It is important to notice that these methods will not consider convection and far infrared radiation, thus the absorbed-reemited heat will not be considered.

On the other hand, depending on the geometry of your facade system, it might be worth calculating the BSDF (using genBSDF). Then, the BSDF may be imported to Window for estimating solar heat gain coefficient, considering convection and FIR radiation.

If you want to avoid Window, the method used by it to calculate absorption on each layer is very well documented y two papers by J.H.Klems. Then, ISO15099 will give you a hint on how to calculate the solar heat gain coefficient from all the information you have at that point.

Those three components would allow you, respectively, to:

1. Calculate transmission and reflection of each layer (genbsdf)
2. Calculate absorption on each layer (Klems)
3. Calculate the inward flowing fraction of the absorbed radiation (iso15099)

Yes... Avoiding windows is hard.

Best,
El 7 abr. 2016 03:23, "Achim Geissler" <achim.geissler@intergga.ch<mailto:achim.geissler@intergga.ch>> escribió:
Dear Séverine,

from my point of view, if your interest lies with solar >energy< gain, then Radiance is not really best suited. Typically, what you describe is covered by thermal building simulation tools to a quite high degree of detail (ESP-r, EnergyPlus, IDA-ICE, TRNSYS to name a few). It would likely be quite difficult or probably even impossible e.g. to model the secondary heat gain through windows / glazed facades (or opaque facades, for that matter). Also, “what goes through” is not the whole story. What happens in the building is also of major interest to be able to decide if the gains are “useful” or “harmful”.

Why do you think you need the ray tracing approach?

Best
Achim

Von: Séverine HUET [mailto:S.HUET@vs-a.eu<mailto:S.HUET@vs-a.eu>]
Gesendet: Mittwoch, 6. April 2016 15:35
An: radiance-general@radiance-online.org<mailto:radiance-general@radiance-online.org>
Betreff: [Radiance-general] Asking for informations

[VS-A.jpg]

VS-A

architectes d.p.l.g / ingénierie de l’enveloppe

Hi Radiance team,

I am a student in an engineering school and I am currently doing an internship in a design office specialized in building envelope studies.

My work consist in developing a tool to determine precisely the solar factor of a facade, taking into account its shading devices and its geometry which can be complex sometimes.

My idea is to use the software Grasshopper to:

1. Import a geometry

2. Define the materials of the scene

3. Create the Radiance geometry

4. Create two analysis grid (vertical): one before the system “shading+facade” to determine the incident solar energy, and one inside my building to determine the transmitted solar energy.

5. Then, use the Ray Tracing method to calculate the solar energy on each point…
This method seems interesting for my problematic but the calculations under the hood may be not relevant for solar energy, insofar as it is designed for light calculations and realistic rendering.

Questions :

1) I apology if I am missing something obvious, I have done some researches about the “Ray tracing” method used by Radiance but I still have some interrogations about how it works… Is the ray divided in many rays when it punch a surface ? What is the different between the direct light and the diffuse light (in terms of modeling) ? Is there a way to convert R G B radiance provided by Radiance in solar energy for instance (like it is done for luminance) ?

2) I must not be the first to process this kind of problematic, so I am wondering if it exists a calculation engine derived from Radiance which can provide the solar energy using a kind of “ray tracing” method?

For me, in principle, it is not that complicated, I mean it is possible. The problematic is purely geometric and mathematic. I imagine: the ray launched is define by a wave length, an intensity and a direction (to model the direct radiation). When it reaches a surface, the intensity took into account is the intensity of the surface’s normal projection of the ray. Then the ray is divided in 3 rays: one transmitted, one reflected and one absorbed, whose proportions (in terms of intensity) and directions depend on the material definition of the surface reached. This last can react differently according to wavelength domain of the ray. Do the same with diffuse rays, to model the diffuse radiation. The absorbed part of the incident energy could be transformed in heat (Infrared radiation) according to the emissivity of the surface.

I am sorry about the lenth of the message. I really need to understand how I can do to determine solar energy through different kind of materials (translucent, transparent, opaque…). I would be really thankful if you help me! This project constitute my graduation project, it is quite ambitious that’s why I need some guidelines.

Thank you in advance,
Yours sincerely

Severine Huet

VS-A, architectes d.p.l.g / ingénierie de l’enveloppe

41 place Rihour / F-59000 LILLE – France
Tél : +33 (0)3.20.52.11.44<tel:%2B33%20%280%293.20.52.11.44> ; Ligne directe : +33 (0)3.20.52.xx.xx / Fax : +33 (0)3.20.52.05.15<tel:%2B33%20%280%293.20.52.05.15>
email : courrier@vs-a.eu<mailto:courrier@vs-a.eu> / email direct : S.HUET@vs-a.eu<mailto:S.HUET@vs-a.eu> / www.vs-a.eu<http://www.vs-a.eu>

Ce courriel (et ses pièces jointes) est adressé exclusivement à son destinataire ; il n’a pas de valeur hors de ce contexte précis et peut être confidentiel. Nous remercions d’avance les destinataires involontaires de s’abstenir de le dupliquer de quelque manière que ce soit, et de le détruire. Merci également de bien vouloir en avertir l’expéditeur.

This e-mail (and its attachments) is intended to be for the only use of its recipient; the message is worthless out of this specific context and may contain confidential information. If you have received this e-mail by mistake, please do not duplicate it in any possible way. Thank you as well for notifying us immediately and deleting this e-mail.

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Christopher,

thanks for the “heads up”. I retracted because the original question was towards “solar factor” (I assume SHGC) of facades, not actually “what happens in the space behind the facade” as far as my second, somewhat closer reading revealed. As you write, the programs mentioned by me originally are less adept in giving detailed answers to this question (with the possible exception of ESP-r, which can be used as kind of a non-building-focused “physics toolkit”).

So, to my understanding the goal seems to be a tool to calculate SHGC of facades with (complex) shading systems. However, as SHGC includes secondary heat flux (re-distribution of absorbed solar radiation), I am not quite sure how Radiance can really help, here. Therefore my support of Germán / ISO 15099 (e.g. WIS has been shown to give good agreement with measurement results for ventilated double facades with venetian blinds in the facade gap). Also, e.g. in the U.K. it became increasingly normal a few years ago to include framing / panels in facade-SHGC values. Therefore possibly the Physibel products.

I agree that the central question of interest should be clarified in detail first. And I would also hesitate to think it realistic to actually develop a new tool that has any advantage over one of the available ones. But, then, I’m quite out of programming and am not up to date to current development speeds possible.

Best
Achim

···

On 07 Apr 2016, at 17:26, Christopher Rush <Christopher.Rush@arup.com> wrote:

Achim,
I would say your answer is an important one to keep in mind, regarding the limitations of any chosen process and how the information will be used. Is the intent for system peak capacity relying on comprehensive energy accounting? Or only relative performance comparison of shading systems where insulation properties would be similar amongst them all?

I’m not an expert in the software you listed (ESP-r, EnergyPlus, IDA-ICE, TRNSYS, etc.), but I do suspect some or all of them may have limited accuracy in angular dependent complex fenestration. By my guess they might be able to do reasonably well at comprehensive energy modeling of a simple overhang or external light shelf. But if you have a custom designed louver system you may get more accurate direct radiation calculations using Radiance. However if it’s important for your intentions, you would certainly need some other energy modeling tools to consider the bigger picture of heat transfer (insulation, etc.).

-Chris

From: Achim Geissler [mailto:achim.geissler@intergga.ch <mailto:achim.geissler@intergga.ch>]
Sent: Thursday, April 07, 2016 10:26 AM
To: 'Radiance general discussion'
Subject: Re: [Radiance-general] Asking for informations

Dear Séverine,

I retract my answer from this morning – not quite awake yet, sorry. Basically, I would support Germán. There is also the tool WIS available, which (also) calculates according to ISO 15099. Depending on the level of detail you are seeking, it may be of interest to look at the Tools “TRISCO/VOLTRA” from Physibel. These would also include thermal transport through framing etc. if you are thinking of curtain walls (lots of metal, often). They are slightly less capable in terms of glass description but geared toward energy.

Anyway, developing a tool which goes beyond the mentioned (in depth of detail and accuracy) is definitely not an easy task … good luck!

Best
Achim

Von: Germán Molina Larrain [mailto:germolinal@gmail.com <mailto:germolinal@gmail.com>]
Gesendet: Donnerstag, 7. April 2016 13:48
An: Radiance general discussion
Betreff: Re: [Radiance-general] Asking for informations

Hi Séverine,

I often use Radiance for performing calculations in the solar range. In that case, I just use grey surfaces (R=G=B=solar reflectance), and ask the Perez sky models to give me solar instead of visible Radiance (I think this is done using O1 option in the command line).

It is important to notice that these methods will not consider convection and far infrared radiation, thus the absorbed-reemited heat will not be considered.

On the other hand, depending on the geometry of your facade system, it might be worth calculating the BSDF (using genBSDF). Then, the BSDF may be imported to Window for estimating solar heat gain coefficient, considering convection and FIR radiation.

If you want to avoid Window, the method used by it to calculate absorption on each layer is very well documented y two papers by J.H.Klems. Then, ISO15099 will give you a hint on how to calculate the solar heat gain coefficient from all the information you have at that point.

Those three components would allow you, respectively, to:

1. Calculate transmission and reflection of each layer (genbsdf)
2. Calculate absorption on each layer (Klems)
3. Calculate the inward flowing fraction of the absorbed radiation (iso15099)

Yes... Avoiding windows is hard.

Best,

El 7 abr. 2016 03:23, "Achim Geissler" <achim.geissler@intergga.ch <mailto:achim.geissler@intergga.ch>> escribió:
Dear Séverine,

from my point of view, if your interest lies with solar >energy< gain, then Radiance is not really best suited. Typically, what you describe is covered by thermal building simulation tools to a quite high degree of detail (ESP-r, EnergyPlus, IDA-ICE, TRNSYS to name a few). It would likely be quite difficult or probably even impossible e.g. to model the secondary heat gain through windows / glazed facades (or opaque facades, for that matter). Also, “what goes through” is not the whole story. What happens in the building is also of major interest to be able to decide if the gains are “useful” or “harmful”.

Why do you think you need the ray tracing approach?

Best
Achim

Von: Séverine HUET [mailto:S.HUET@vs-a.eu <mailto:S.HUET@vs-a.eu>]
Gesendet: Mittwoch, 6. April 2016 15:35
An: radiance-general@radiance-online.org <mailto:radiance-general@radiance-online.org>
Betreff: [Radiance-general] Asking for informations

<image001.jpg>
VS-A

architectes d.p.l.g / ingénierie de l’enveloppe

Hi Radiance team,

I am a student in an engineering school and I am currently doing an internship in a design office specialized in building envelope studies.

My work consist in developing a tool to determine precisely the solar factor of a facade, taking into account its shading devices and its geometry which can be complex sometimes.

My idea is to use the software Grasshopper to:
1. Import a geometry

2. Define the materials of the scene

3. Create the Radiance geometry

4. Create two analysis grid (vertical): one before the system “shading+facade” to determine the incident solar energy, and one inside my building to determine the transmitted solar energy.

5. Then, use the Ray Tracing method to calculate the solar energy on each point…

This method seems interesting for my problematic but the calculations under the hood may be not relevant for solar energy, insofar as it is designed for light calculations and realistic rendering.

Questions :
1) I apology if I am missing something obvious, I have done some researches about the “Ray tracing” method used by Radiance but I still have some interrogations about how it works… Is the ray divided in many rays when it punch a surface ? What is the different between the direct light and the diffuse light (in terms of modeling) ? Is there a way to convert R G B radiance provided by Radiance in solar energy for instance (like it is done for luminance) ?

2) I must not be the first to process this kind of problematic, so I am wondering if it exists a calculation engine derived from Radiance which can provide the solar energy using a kind of “ray tracing” method?

For me, in principle, it is not that complicated, I mean it is possible. The problematic is purely geometric and mathematic. I imagine: the ray launched is define by a wave length, an intensity and a direction (to model the direct radiation). When it reaches a surface, the intensity took into account is the intensity of the surface’s normal projection of the ray. Then the ray is divided in 3 rays: one transmitted, one reflected and one absorbed, whose proportions (in terms of intensity) and directions depend on the material definition of the surface reached. This last can react differently according to wavelength domain of the ray. Do the same with diffuse rays, to model the diffuse radiation. The absorbed part of the incident energy could be transformed in heat (Infrared radiation) according to the emissivity of the surface.

I am sorry about the lenth of the message. I really need to understand how I can do to determine solar energy through different kind of materials (translucent, transparent, opaque…). I would be really thankful if you help me! This project constitute my graduation project, it is quite ambitious that’s why I need some guidelines.

Thank you in advance,
Yours sincerely

Severine Huet

VS-A, architectes d.p.l.g / ingénierie de l’enveloppe

41 place Rihour / F-59000 LILLE – France
Tél : +33 (0)3.20.52.11.44 <tel:%2B33%20%280%293.20.52.11.44> ; Ligne directe : +33 (0)3.20.52.xx.xx / Fax : +33 (0)3.20.52.05.15 <tel:%2B33%20%280%293.20.52.05.15>
email : courrier@vs-a.eu <mailto:courrier@vs-a.eu> / email direct : S.HUET@vs-a.eu <mailto:S.HUET@vs-a.eu> / www.vs-a.eu <http://www.vs-a.eu/>

Ce courriel (et ses pièces jointes) est adressé exclusivement à son destinataire ; il n’a pas de valeur hors de ce contexte précis et peut être confidentiel. Nous remercions d’avance les destinataires involontaires de s’abstenir de le dupliquer de quelque manière que ce soit, et de le détruire. Merci également de bien vouloir en avertir l’expéditeur.

This e-mail (and its attachments) is intended to be for the only use of its recipient; the message is worthless out of this specific context and may contain confidential information. If you have received this e-mail by mistake, please do not duplicate it in any possible way. Thank you as well for notifying us immediately and deleting this e-mail.

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achim.geissler@intergga.ch

Thank you Chris.

From an irradiance image (-i) I didn't realise a multiplier of 1 in falsecolor provided units in W/m^2

I accept the reservations. For this project a gross mapping over a large site with block building shapes, the results can only be construed as indicative.

Regards
*Terrance McMinn*

···

Yes, there is a -m multiplier option to falsecolor, which defaults to -m 179 and should equate to lux or cd/m�. Luminance in cd/m2 is the default label to display luminance unless you give the -l lux option for example for illuminance � both related to the 179 lumen/Watt multiplier.

However for Watts you can use -m 1 in your options to falsecolor along with -l W/m2 to change the label to display as W/m2. That is presuming your image is calculated with -i option for irradiance. I don�t think people would normally expect to see a Watts based radiance image in W/sr/m2.

This is also presuming the intent of your image takes into account all the shortcomings that Achim noted.

*From:*Terrance McMinn [mailto:t.mcminn@ocpms.com.au]
*Sent:* Thursday, April 07, 2016 9:39 AM

Can you configure falsecolor to map as w/sqm?

____________________________________________________________
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Follow up question:

Using gendaylit rather than the gensky sky generator we have additional -O options. -O 1 for W/m^2/sr solar radiation.

    /From the gendaylit man page:
    The output can be set to either the radiance of the visible
    radiation, the solar radiance (full spectrum) or the luminance.
    //*-O*//[0|1|2] (0=output in W/m^2/sr visible radiation (default),
    1=output in W/m^2/sr solar radiation, 2=output in lm/m^2/sr luminance)./

Looking at the source code it appears the -O 0 option divides illuminance by 179 whilst the -O 1 and -O 2 don't. I couldn't see how the units are outputted from gensky (in relation to the 179 multiplier) to allow me to compare it to the gendaylit options.

One might assume that the -O 0 option would be set to similar units as the gensky generator.

From this confusion what multiplier should be used with the falsecolor program when using gendaylit options 0, 1 and 2 remembering that falsecolor has the default -m 179?

(I all cases I would be using the rpict -i option and looking for units in W/m^2)

Regards
*Terrance McMinn*

···

On 8/04/2016 10:27 am, Terrance McMinn wrote:

Thank you Chris.

From an irradiance image (-i) I didn't realise a multiplier of 1 in falsecolor provided units in W/m^2

I accept the reservations. For this project a gross mapping over a large site with block building shapes, the results can only be construed as indicative.

Regards
*Terrance McMinn*

Yes, there is a -m multiplier option to falsecolor, which defaults to -m 179 and should equate to lux or cd/m�. Luminance in cd/m2 is the default label to display luminance unless you give the -l lux option for example for illuminance � both related to the 179 lumen/Watt multiplier.

However for Watts you can use -m 1 in your options to falsecolor along with -l W/m2 to change the label to display as W/m2. That is presuming your image is calculated with -i option for irradiance. I don�t think people would normally expect to see a Watts based radiance image in W/sr/m2.

This is also presuming the intent of your image takes into account all the shortcomings that Achim noted.

*From:*Terrance McMinn [mailto:t.mcminn@ocpms.com.au]
*Sent:* Thursday, April 07, 2016 9:39 AM

Can you configure falsecolor to map as w/sqm?

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

From my understanding,

   1. -O0 will give you a Perez Sky... similar to the Gensky output, but
   using a diferent sky model. This model does not need to be told if the sky
   is overcast or clear. It will figure that out itself.
   2. -O1 will give you the Perez Sky but with for the solar spectrum (i.e.
   solar radiation calculation)
   3. -O2 is something that I wonder why is there.

If you want your output on Watts (or any energy unit), you should use a
multiplier of 1. For Lighting units (lux, cd, lumens) you need a multiplier
of 179.....I do not usually make pictures... but I hope the few I have done
were correct.

Best.

···

2016-04-14 8:21 GMT-03:00 Terrance McMinn <t.mcminn@ocpms.com.au>:

Follow up question:

Using gendaylit rather than the gensky sky generator we have additional -O
options. -O 1 for W/m^2/sr solar radiation.

*From the gendaylit man page: The output can be set to either the radiance
of the visible radiation, the solar radiance (full spectrum) or the
luminance. **-O**[0|1|2] (0=output in W/m^2/sr visible radiation
(default), 1=output in W/m^2/sr solar radiation, 2=output in lm/m^2/sr
luminance).*

Looking at the source code it appears the -O 0 option divides illuminance
by 179 whilst the -O 1 and -O 2 don't. I couldn't see how the units are
outputted from gensky (in relation to the 179 multiplier) to allow me to
compare it to the gendaylit options.

One might assume that the -O 0 option would be set to similar units as the
gensky generator.

From this confusion what multiplier should be used with the falsecolor
program when using gendaylit options 0, 1 and 2 remembering that falsecolor
has the default -m 179?

(I all cases I would be using the rpict -i option and looking for units in
W/m^2)

Regards
*Terrance McMinn*

On 8/04/2016 10:27 am, Terrance McMinn wrote:

Thank you Chris.

From an irradiance image (-i) I didn't realise a multiplier of 1 in
falsecolor provided units in W/m2

I accept the reservations. For this project a gross mapping over a large
site with block building shapes, the results can only be construed as
indicative.

Regards
*Terrance McMinn*

Yes, there is a -m multiplier option to falsecolor, which defaults to
   -m 179 and should equate to lux or cd/m². Luminance in cd/m2 is the
default label to display luminance unless you give the -l lux option
for example for illuminance – both related to the 179 lumen/Watt multiplier.

However for Watts you can use -m 1 in your options to falsecolor
along with -l W/m2 to change the label to display as W/m2. That is
presuming your image is calculated with -i option for irradiance. I don’t
think people would normally expect to see a Watts based radiance image in
W/sr/m2.

This is also presuming the intent of your image takes into account all the
shortcomings that Achim noted.

*From:* Terrance McMinn [mailto:t.mcminn@ocpms.com.au
<t.mcminn@ocpms.com.au>]
*Sent:* Thursday, April 07, 2016 9:39 AM

Can you configure falsecolor to map as w/sqm?

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

_______________________________________________
Radiance-general mailing list
Radiance-general@radiance-online.org
http://www.radiance-online.org/mailman/listinfo/radiance-general

To further expand on the multiplier question… here’s my interpretation to be corrected if anyone understands differently…
-O 0 would give Watts of energy within the visible spectrum in the sky model, and apply the default 179 multiplier to convert to lumens in any outputs.
-O 1 would give Watts of energy across the full solar spectrum in the sky model, and typically would have to set a multiplier of 1 to keep Watts in any outputs.
-O 2 would give lumens of energy in the visible spectrum in the sky model, and you would have to set a multiplier of 1 to keep that in any outputs. I agree I’m not sure why to do this instead of the default 179 multiplier.

···

From: Germán Molina Larrain [mailto:germolinal@gmail.com]
Sent: Thursday, April 14, 2016 8:36 AM
To: Radiance general discussion
Subject: Re: [Radiance-general] Asking for informations

From my understanding,

  1. -O0 will give you a Perez Sky... similar to the Gensky output, but using a diferent sky model. This model does not need to be told if the sky is overcast or clear. It will figure that out itself.
  2. -O1 will give you the Perez Sky but with for the solar spectrum (i.e. solar radiation calculation)
  3. -O2 is something that I wonder why is there.

If you want your output on Watts (or any energy unit), you should use a multiplier of 1. For Lighting units (lux, cd, lumens) you need a multiplier of 179.....I do not usually make pictures... but I hope the few I have done were correct.

Best.

2016-04-14 8:21 GMT-03:00 Terrance McMinn <t.mcminn@ocpms.com.au<mailto:t.mcminn@ocpms.com.au>>:
Follow up question:

Using gendaylit rather than the gensky sky generator we have additional -O options. -O 1 for W/m^2/sr solar radiation.
From the gendaylit man page:
The output can be set to either the radiance of the visible radiation, the solar radiance (full spectrum) or the luminance. -O[0|1|2] (0=output in W/m^2/sr visible radiation (default), 1=output in W/m^2/sr solar radiation, 2=output in lm/m^2/sr luminance).
Looking at the source code it appears the -O 0 option divides illuminance by 179 whilst the -O 1 and -O 2 don't. I couldn't see how the units are outputted from gensky (in relation to the 179 multiplier) to allow me to compare it to the gendaylit options.

One might assume that the -O 0 option would be set to similar units as the gensky generator.

From this confusion what multiplier should be used with the falsecolor program when using gendaylit options 0, 1 and 2 remembering that falsecolor has the default -m 179?

(I all cases I would be using the rpict -i option and looking for units in W/m^2)
Regards
Terrance McMinn
On 8/04/2016 10:27 am, Terrance McMinn wrote:

Thank you Chris.

From an irradiance image (-i) I didn't realise a multiplier of 1 in falsecolor provided units in W/m2

I accept the reservations. For this project a gross mapping over a large site with block building shapes, the results can only be construed as indicative.
Regards
Terrance McMinn
Yes, there is a -m multiplier option to falsecolor, which defaults to -m 179 and should equate to lux or cd/m². Luminance in cd/m2 is the default label to display luminance unless you give the -l lux option for example for illuminance – both related to the 179 lumen/Watt multiplier.

However for Watts you can use -m 1 in your options to falsecolor along with -l W/m2 to change the label to display as W/m2. That is presuming your image is calculated with -i option for irradiance. I don’t think people would normally expect to see a Watts based radiance image in W/sr/m2.

This is also presuming the intent of your image takes into account all the shortcomings that Achim noted.

From: Terrance McMinn [mailto:t.mcminn@ocpms.com.au]
Sent: Thursday, April 07, 2016 9:39 AM
Can you configure falsecolor to map as w/sqm?

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

_______________________________________________
Radiance-general mailing list
Radiance-general@radiance-online.org<mailto:Radiance-general@radiance-online.org>
http://www.radiance-online.org/mailman/listinfo/radiance-general

some more explanations:

about gendaylit:
to understand the output you have to know what gendaylit does and on what models it is based:
Gendaylit uses
- a sky luminance distribution model according to Perez ( details and publication reference see manpage),
- a luminance efficacy model according to Perez(details and publication reference see manpage), because the conversion factor between solar spectrum units and photometric units (=luminance efficacy) is changing depending on the sky type and situation (for example, close to sunset, the infrared proportion of the radiation increases a lot)
- it generates automatically the skytype based on the radiation data (and time and location)
Gendaylit assumes, that the input is given via the -W (direct normal,diffuse horizontal) or -G (direct horizontal and diffuse horizontal) is radiation in the solar spectrum.
The output option -O 1 does not apply any luminance efficacy model, but is using the Perez sky distribution. Therefore when you "put in" solar spectrum you get also radiometric units as output. e.g. if you run rtrace -I , then the output is directly W/m2.
The output option -O 2 applies the the Perez sky distribution AND the luminance efficacy model. The output units are directly in photometric quantities. e.g. if you run rtrace -I you get directly a lux value.
The output option -O 0 (default) does the same as the -O 2 option EXCEPT the output is divided by 179. This is mainly done to be consistent with the output of gensky.

about gensky:
it generates sky distributions according to the CIE model. you have to specify explicitly the sky type (sunny, overcast...)
gensky does not apply any luminance efficacy model (at least I don't know any option to do so) . So you get as output unit what you put into it! So if you put in a solar spectrum power, then your output is also radiometric. If you put in only the power in the visible range, then you get the photometric quantities.
But don't put in radiometric and then expect the output to be photometric quantities!! The 179lm/W conversion is not a luminance efficacy model, it is just a "chosen" convention to calculate from the radiation (in the visual spectrum) to the photometric quantities. It does not take into account, that for example the luminance efficacy of the sun is between 80-100 lm/W (or during sunset it drops to 50 lm/W), whereas an overcast sky has about 130 lm/W.

as conclusion:
When you are just interested in the solar spectrum, then the difference for a specific skytype (e.g. completely sunny) between gendaylit -O 1 and gensky is "only" the sky luminance distribution.
When you are interested in photometric quantities AND your input data is based on the solar spectrum(e.g. from a EPW file or measured), then you should use gendaylit only (except you calculate externally the luminance efficacy and run then gensky).

Jan

···

On 14/04/16 20:47, Christopher Rush wrote:

To further expand on the multiplier question� here�s my interpretation to be corrected if anyone understands differently�

-O 0 would give Watts of energy within the visible spectrum in the sky model, and apply the default 179 multiplier to convert to lumens in any outputs.

-O 1 would give Watts of energy across the full solar spectrum in the sky model, and typically would have to set a multiplier of 1 to keep Watts in any outputs.

-O 2 would give lumens of energy in the visible spectrum in the sky model, and you would have to set a multiplier of 1 to keep that in any outputs. I agree I�m not sure why to do this instead of the default 179 multiplier.

*From:*Germ�n Molina Larrain [mailto:germolinal@gmail.com]
*Sent:* Thursday, April 14, 2016 8:36 AM
*To:* Radiance general discussion
*Subject:* Re: [Radiance-general] Asking for informations

From my understanding,

1. -O0 will give you a Perez Sky... similar to the Gensky output, but
    using a diferent sky model. This model does not need to be told if
    the sky is overcast or clear. It will figure that out itself.
2. -O1 will give you the Perez Sky but with for the solar spectrum
    (i.e. solar radiation calculation)
3. -O2 is something that I wonder why is there.

If you want your output on Watts (or any energy unit), you should use a multiplier of 1. For Lighting units (lux, cd, lumens) you need a multiplier of 179.....I do not usually make pictures... but I hope the few I have done were correct.

Best.

2016-04-14 8:21 GMT-03:00 Terrance McMinn <t.mcminn@ocpms.com.au <mailto:t.mcminn@ocpms.com.au>>:

    Follow up question:

    Using gendaylit rather than the gensky sky generator we have
    additional -O options. -O 1 for W/m^2/sr solar radiation.

        /From the gendaylit man page:
        The output can be set to either the radiance of the visible
        radiation, the solar radiance (full spectrum) or the
        luminance. *-O*[0|1|2] (0=output in W/m^2/sr visible radiation
        (default), 1=output in W/m^2/sr solar radiation, 2=output in
        lm/m^2/sr luminance)./

    Looking at the source code it appears the -O 0 option divides
    illuminance by 179 whilst the -O 1 and -O 2 don't. I couldn't see
    how the units are outputted from gensky (in relation to the 179
    multiplier) to allow me to compare it to the gendaylit options.

    One might assume that the -O 0 option would be set to similar
    units as the gensky generator.

    From this confusion what multiplier should be used with the
    falsecolor program when using gendaylit options 0, 1 and 2
    remembering that falsecolor has the default -m 179?

    (I all cases I would be using the rpict -i option and looking for
    units in W/m^2)

    Regards
    *Terrance McMinn*

    On 8/04/2016 10:27 am, Terrance McMinn wrote:

        Thank you Chris.

        From an irradiance image (-i) I didn't realise a multiplier of
        1 in falsecolor provided units in W/m^2

        I accept the reservations. For this project a gross mapping
        over a large site with block building shapes, the results can
        only be construed as indicative.

        Regards
        *Terrance McMinn*

            Yes, there is a -m multiplier option to falsecolor, which
            defaults to -m 179 and should equate to lux or
            cd/m�. Luminance in cd/m2 is the default label to display
            luminance unless you give the -l lux option for
            example for illuminance � both related to the 179
            lumen/Watt multiplier.

            However for Watts you can use -m 1 in your options
            to falsecolor along with -l W/m2 to change the label
            to display as W/m2. That is presuming your image is
            calculated with -i option for irradiance. I don�t think
            people would normally expect to see a Watts based radiance
            image in W/sr/m2.

            This is also presuming the intent of your image takes into
            account all the shortcomings that Achim noted.

            *From:*Terrance McMinn [mailto:t.mcminn@ocpms.com.au]
            *Sent:* Thursday, April 07, 2016 9:39 AM

            Can you configure falsecolor to map as w/sqm?

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