SimScale CAE Forum

Thermal comforts in buildings, MRT, PPD, operative temperature

Hello Guys
I wanna talk about indoor cfd and how important thermal comfort is in the building industry.
I came across the situation that we wanted to get the operative temperature. As operative temperature we understand the mean value of air temperature and radiant temperature. The PPD (predicted percentage of dissatisfied) as a indicator of thermal comfort is also depending on the operative temperature. As it currently implemented in Simscale is, that the MRT (mean radiant temperature) is following: The current implementation approximates MRT as a single uniform scalar value throughout the domain, based on a size-weighted average across all domain surface temperatures. The approximation does not take into account view factors and assumes an emissivity of 1..

At the moment the only tool we got to decide if the thermal comfort is in an sufficient range is the PPD.
From my perspective these leads to problems when we have locally really cold surfaces which will result in people freezing.

This situation with locally cold surface is not a rare circumstance. In the building construction , these question about radiate symmetry and operative temperature comes up a lot. Here a comparison between simscale and designbuilder (GUI for openfoam). As you see we have huge differences in radiant temperatures across the model. Left side: Designbuilder , right side: Simscale

How can we solve that?
Im not an OpenFoam expert, but i found that that there is an implementation of the RTE equations called [fvDOM] (https://www.openfoam.com/documentation/guides/latest/api/classFoam_1_1radiation_1_1fvDOM.html)
I hope an Simscale expert can answer me if there are any plans to expand the thermal comfort parameters.

From the perspective of the building construction. These parameters are important for thermal comfort in buildings.

  • operative temperature
  • PPD / PMV
  • DR (draught risk)

Thank you for your time reading this. Im happy to hear some answers and tips.

best regards
david

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Thanks a lot for your input David!

Will immediately forward this to my colleagues - getting back to you soon.

Best,

Jousef

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Hey David,

We are also aware of this and you are correct, we have a simpler implementation at the moment. This will change as we go of course.
In a cuboid/fairly uniform room, we should be pretty OK but once the shape becomes more organic, this can certainly skew the results.
I think a colleague is planning a call with you and I’ll jump on it so we can chat a little more if that is OK?

Best regards,
Jon

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