Error: connect radGlassMat to WindowGroup in 3-Phase method

Hi there!

Hope you have had a good summer by far :slight_smile:
Recently I am exploring 3-Phase recipe in a shoebox room with one window, which covers the whole south facade. I encounter an error regarding radGlassMat to WindowGroup.

I intend to use a single_clear_glazing material with 0.7 visible transmittance. I tried two ways to create the glass material, radBSDFMat and radGlassMat. I test them respectively.
Please see below:

I created the simple glass material in WINDOW7.7. Then I connected the xml file to radBSDFMat and assigned it to WindowGroup. The results showed that radBSDFMat works fine and generates DA and UDI outputs. Please see the below image for the single clear glazing I created:

Then I tired radGlassMat to connect to windowgroup. It comes out with an error. No output was generated:

I am not sure the reason behind the error. According to the reading of The Three-Phase method for simulating complex Fenestration with Radiance. A McNeil, LBNL. (Last revision: 2014), three-phase method is described as:

Flux transfer is broken into the following three phases for independent simulation:

  1. Sky to exterior of fenestration
  2. Transmission through fenestration
  3. Interior of fenestration into the simulated space
    A matrix is used to characterize each phase of light transport. The input condition, sky luminance, is a vector. The result, illuminance values or a rendering, is also vector. The result is achieved by multiplying the sun vector by each matrix representing each phase of flux transfer. The process is described by the following equation:
    i = VTDs, or, I = VTDS
    i = point in time illuminance or luminance result
    I= matrix containing time series of illuminance or luminance result
    V = view matrix, (created with Radiance_rcontrib, vwrays)
    T = transmission matrix. (created by Radiance_genBSDF)
    D = daylight matrix. Daylight matrix contains luminous flux transfer coefficient from the sky divisions to the window’s incident Klems divisions. (created by Radiance_gensklemsamp, rcontrib)

Is it because the single_clear_glazing cannot behave in the transmission matrix so radGlassMat cause an error?

Also, with reviewing discussions in the discourse, I understand 3-phase method is particularly good when using BSDF material. With that said, I am wondering if single clear glazing material is suitable for 3-phase method, and if radGlassMat is allowed to apply to it.
Plus, I am not very clear about the definition of WindowGroup and Window State. Any reference about these concepts will be appreciated.

Thanks for your comments and suggestions. (545.6 KB)

Hi @catsquito ,

Is it because the single_clear_glazing cannot behave in the transmission matrix so radGlassMat cause an error?

Yes, you figured it out exactly. 3-Phase simulations only work with BSDF materials in the window groups since it does the indoor and outdoor ray tracing calculations separately. So 3-Phase requires a complete definition of the relationship between interior and exterior light that passes through each angle of a window. And this definition of the interior/exterior relationship is done via a BSDF (aka. transmission matrix). We should add a better error message in for this at some point and I’m sorry that this unclear Glass object has to attribute 'angle_basis_' is what you get for now.

In one sense, the use of BSDFs is a strength of 3-Phase in that you only need to do the indoor and outdoor ray tracing calculations once and then you can swap out the transmission matrix (BSDF) with whatever window states you want very quickly. This allows you to test out a range of different shade control strategies and, each time you want to see the effect of the strategy, you’re only doing fast matrix multiplications (fast enough to happen in real-time).

However, there are also some downsides, one of which you have already seen in the form of needing to generate the BSDFs for each material. Another downside is that the resolution of the Klems BSDF patches usually doesn’t do a good job modeling direct beam transmission through the window. So 3-Phase isn’t always the best strategy if you are trying to understand things like glare from direct sun. That is, unless you use the TensorTree definition of BSDFs, which has a higher resolution but a huge file size and takes a very long time to run.


Just two quick notes/clarifications:

  1. Honeybee does 3-Phase slightly differently from how a typical 3-phase simulation works. You can include windows with non-bsdf materials in the model but they will go through a 2-phase simulation automatically. See this post here:[-]-set-up-the-input-files-for-multi-phase-daylight-simulation

  2. You cannot use a TensorTree BSDF in 3-Phase for defining the transmission matrix. It must be Klems. You can indeed use a TensorTree BSDF as part of the scene or for the 5th phase of the 5-Phase study. The bad news is that our current UI in honeybee[+] doesn’t support using two different BSDFs for the 3rd and 5th phases of the 5-Phase method. :expressionless: You have to do some extra work to make that happen.