Claculating outdoor MRT: how far should I look for surface temperatures to consider?


I’m working on a UTCI project. To calculate UTCI, one of the inputs is Mean Radiant Temperature (MRT). The component “Outdoor Solar MRT” has an input “_surface_temp”, which is expected. However, the description reads “A single number or an hourly data collection with the temperature of surfaces around the person”.

My question is: which surfaces should I consider? There’s no variable for distance or angle factor between each surface and the human body. I have calculated all surface temperatures, but it wouldn’t make sense to consider surfaces which are 30m away. Plus, computing time would be too high for something that isn’t necessary.


Hi @mateobarbero ,

The ideal solution is to use a weighted average of the surrounding surface temperatures where the weights are derived from the view factors from the human subject to each of the surfaces. So a surface 30m away might matter if the surface is 30m tall. It probably doesn’t matter if it’s 1 m tall. In other words, the distance away that the surface is doesn’t matter and, instead, it’s the fraction of the view around the human subject that matters. You can probably ignore a surface when it occupies less than 1% of the view.

I should also clarify that the Outdoor Solar MRT component is really made to give you rough approximations of outdoor MRT. If you want to run a simulation that includes the calculation of view factors to surfaces, you can use the HB UTCI Comfort Map, which will compute view factors from the model’s sensor points to each of the Room surfaces using Radiance.

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Hi Chris,

A bit late in the conversation. Had similar issue and used HB UTCI comfort map which works out great. However I am wondering whether if it is possible to also get the MRT output for verification purposes?

Furthermore is it possible to add a calculated windspeed (using butterfly) for each point as the input to wind_speed just as it is in the Outdoor UTCI comfort component?

Yes, I just added a component to the latest development version of the plugin that can parse in the inputs to the comfort model. The component is called “HB Read Environment Matrix” and you can get it by running the LB Versioner component and restarting Rhino.

We are working on exposing more easy was to do this. See here for a temporary workaround:


Thank you Chris! It works now and being able to get the MRT from the comfort map makes it possible to workaround the wind problem by using the MRT in the LB UTCI Comfort input.

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