[Radiance-general] Asking for informations

Thu Apr 7 04:47:53 PDT 2016

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 at 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 at vs-a.eu]
> *Gesendet:* Mittwoch, 6. April 2016 15:35
> *An:* radiance-general at 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 at vs-a.eu  / email direct : S.HUET at vs-a.eu / www.vs-a.eu
>
>
>
>
>
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>
>
>
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