[Radiance-general] Asking for informations

Thu Apr 7 09:43:09 PDT 2016

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 at 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 at intergga.ch <mailto:achim.geissler at 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 at gmail.com <mailto:germolinal at 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 at intergga.ch <mailto: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 <mailto:S.HUET at vs-a.eu>] 
> Gesendet: Mittwoch, 6. April 2016 15:35
> An: radiance-general at radiance-online.org <mailto:radiance-general at 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
>  
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