Dragonfly / Unable to apply custom ConstructionSet?

Hi everyone,

I’ve been using Dragonfly (from LBT 1.3.0) to generate “alternative EPW files” thanks to the UWG model.

My goal is to study the impact of different wall materials on the air temperature inside the urban canyon. The point was to analyze not only the impact of albedo but also of the walls’ thickness, density and specific heat.

I first thought that I would:

  • create own Honeybee ConstructionSets (that take into account all those properties)
  • plug my ConstructionSets into the DF Building from Solid component
  • and use the resulting Dragonfly buildings as input for my Dragonfly Model

Then I realized that I had to go through the DF Assign Building UWG Properties which takes as input the vintage of the building and maps it to one of the three options (New ; 1980-Present ; Pre1980).

Am I right to assume that all the ConstructionSets that I defined are erased by DF Assign Building UWG Properties ? Does this mean that I cannot study the impact of different walls’ thickness, density and specific heat ?
Is there a way to somehow bypass DF Assign Building UWG Properties, if maybe UWG can accept other inputs that the 3 generic ones (New ; 1980-Present ; Pre1980) ?

Thanks in advance!

Hi @JulienFBC ,

It’s important to clarify that nothing is erased by the “Assign Building UWG Properties” component. It’s just that the UWG properties of a dragonfly building are completely separate from the EnergyPlus/OpenStudio/URBANopt ones. There are a few places where we try to infer the UWG properties from the EnergyPlus ones (we try to do this with the the program if we can). But mapping EnergyPlus constructions to UWG ones is a little more challenging. It’s not impossible but it would just take a lot of checks to be sure that the UWG reliably gets something that doesn’t cause it to crash. The UWG’s tolerance for material layers with low thermal mass isn’t nearly as high as EnergyPlus’s. So, to make things manage-able for ourselves, we just decided that assigning the UWG constructions from the energy ones just isn’t supported right now. We’ve only exposed a few critical properties of the constructions like albedo, vegetation, and the vintage of the building code governing the constructions.

If you really want to create your own custom constructions for the UWG, this is possible by editing the JSON that dragonfly outputs, which is directly consumed by the UWG. @SaeranVasanthakumar did a good job documenting the schema of these UWG jsons here. And you’ll see that the schema supports the creation of Elements and Materials that can be assigned to the BEMDef. And you can run the JSON through the UWG over command line using the UWG CLI. So that’s the route to go if you need this level of control over the UWG simulation.

Hi Chris,

Thank you very much for your detailed answer. I get your point. I’m definitely gonna try this route with the JSON, I’ll let you know if go through it or face new obstacles.


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