This recipe uses EnergyPlus to obtain longwave radiant temperatures and indoor air
temperatures. The outdoor air temperature and air speed are taken directly from
the EPW. A Radiance-based, enhanced 2-phase method is used for shortwave MRT
calculations, which uses an accurate direct sun calculation with precise solar
positions.
Is there a documentation on how the longwave radiant temperatures and the shortwave MRT are used in the UTCI calculation? A pointer toward the relevant section of the source code will suffice.
Is there a way to dump the input values used in the UTCI calculation?
There isn’t anything too complex about this. The MRT that goes into the UTCI model is essentially essentially just longwave_mrt + shortwave_mrt_delta. Longwave MRT is dictated by the temperature of surrounding surfaces and the sky temperature. It’s essentially the outcome of heat exchange in really low frequency infrared wavelengths. Shortwave solar includes all of the visible solar energy from the sun as well as near infrared (and a little ultraviolet). It’s directly related to the solar irradaince (in W/m2) that we get out of Radiance. Essentially, the irradiance gets plugged into the ASHRAE-55 SolarCal model to convert it into an MRT delta experienced by a human. The documentation on the SolarCal model in Ladybug Tools can be found here along with appropriate references.
I just added the ability to do this in the very latest version of the LBT plugin that you can get with the LB Versioner. If you run that component and then restart Rhino, you’ll see the latest UTCI recipe has an env_conds output, which you can plug into a new component called “HB Read Environmental Matrix” to load either the MRT, Longwave MRT, and Shortwave MRT into Grasshopper.
Hi chris,
I was using the honeybee utci component and found that the I can only get the data of LongwaveMRT, Air temprature and Relative humidity from the env_conds output. I also checked all the result from the recipe folder and it seems like the shortwave MRT and MRT failed to collect the data, could you give me some advice about it?
Hi @chris!
I’m running an outdoor comfort simulation using Ladybug Tools 1.8 and extracting MRT values from the HB UTCI component. However, I noticed that the MRT values provided by UTCI do not match the expected sum: “longwave_mrt + shortwave_mrt_delta”
The MRT values are extracted directly from the HB UTCI component and compared to the sum of longwave_mrt + shortwave_mrt_delta. I’m trying to understand whether this discrepancy is due to an issue in my model or if the UTCI calculation applies any additional corrections that I’m not accounting for.
Additionally, I was wondering whether such high MRT values are plausible. The data refer to the 09:00 - 12:00 time range, with:
Average air temperature: 28°C
Average relative humidity: 55.5%
I’ve attached an image comparing the MRT values from UTCI with those obtained by summing longwave_mrt + shortwave_mrt_delta, along with the climate data for reference.
Does the UTCI model apply any additional corrections or adjustments to MRT that are not directly accounted for in the simple sum?
Any insights would be greatly appreciated!
Thanks in advance,
Sara
