UTCI vs PET for outdoor comfort studies

ladybug-tools
1

Hi,

I’ve been struggling to understand two outdoor comfort indicators and find them quite confusing. The first one, UTCI (Universal Thermal Climate Index), assumes a person walking at 4 km/h (which equals 2.4 metabolic equivalents or met), adaptive clothing insulation, and a wind speed measured at a 10-meter height. The second one, PET (Physiological Equivalent Temperature), requires specific met and clo (clothing insulation) values for its calculations. In my case, I’ve used the same met value as UTCI for a walking person and applied the LB_Clo by temperature method for clo levels—using a clo value of 2 for temperatures below -5°C and 0.46 for temperatures above 26°C.

I expected the results from both indicators to be similar, but they show quite different comfort categories. According to the UTCI results, there’s no sensation of cold at any time of the year. However, the PET results indicate a significant number of hours where the sensation is cold, and the same inconsistency appears when assessing hot sensations. It seems that PET is more sensitive to certain parameters than UTCI, especially when fewer categories are involved.

Does anyone know why this is happening? If so, could you please shed some light on the topic?

Thanks

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UTCI vs PET.gh (47.7 KB)

2

Hi,

Any insight on this? how do you assess whether to use UTCI or PET? on which situations do you use one or the other?

If I am correct, the only recommendation is to use UTCI for most situations and PET only when there is a specific clothing, activity, or personal characteristic (age, gender,…); that is, for more particular scenarios.

Thanks

3

Hi,

Which outdoor comfort model would provide more valuable insights for a stadium seating area or an open railway station?

I’ve noticed significant differences in how these models handle colder conditions. UTCI appears to assume a broad tolerance for cold scenarios, presuming that individuals will wear very thick clothing. In contrast, PET and the adaptive clothing tool seem to better represent cold situations more realistically.

Can anyone offer guidance on when it’s more appropriate to use one model over the other, depending on the specific context or climate?

Thanks