This is an old revision of the document!


PET

The Physiologal Equivalent Temperature (PET) is a thermal comfort index that is based on a prognostic model of the human energy balance that computes the skin temperature, the body core temperature, the sweat rate and, as an auxiliary variable, the clothing temperature. It is generally based on the 2-node model proposed by Gagge et al. (1971) and was compiled and extended by Höppe (1984) to the Munich Energy Balance Model for Individuals (MEMI). The core model can be used both in an instationary and a stationary approach, but for PET only the stationary solution of the body parameters is used.

The Physiologal Equivalent Temperature (PET) is defined as..
..the air temperature at which, in a typical indoor setting (without wind and solar radiation), the heat budget of the human body is balanced with the same core and skin temperature as under the complex outdoor conditions to be assessed
Höppe (1999)

Despite its popularity, PET lacks a proper and comprehensive documentation. Basically, one needs to read the 2 papers Gagge et al. (1971) and Höppe (1984) -in german- plus the computer source code provided by VDI 3787.
It has to be noted, that there are some unlogical assumptions and errors in the original set of equations. In the ENVI-met implementation, these errors have been corrected. As a consequence, PET values calculated by ENVI-met may differ from values calculated by other programs, but we see no sense in copying wrong code or unlogical assumptions. Fundamental changes from the original are marked in the description.

-The description still need to be compiled and written, please hold on-

Main changes to original PET in short :

  • For the indoor setting, the turbulent exchange coefficients for heat and vapour are calculated using the indoor air velocity instead of keeping them at the outdoor value
  • The sweat rate and the amount of sweat on the skin is reseted when calculating the indoor environment

General Idea

The general idea behind PET (and other outdoor thermal comfort indices) is that we can express the thermal comfort of a human body using the skin and core temperature as reference indicators.

So, the basic idea behind PET for an outdoor setting is

  1. Define all incoming and outgoing fluxes at the human body
  2. Calculate a skin and a core temperature, that matches all the calculated fluxes
  3. Transpone the person into an indoor environment
  4. Reset all data that are not available in an indoor environment (direct solar radiation, forced wind movement)
  5. Search for an indoor air temperature (as only parameter) that results in the same skin temperature and core temperature as the outdoor setting.
  6. This theoretically indoor temperature is called PET.

References

  • Gagge, A., Stolwijk, J., and Nishi, Y. (1971): An effective temperature scale based on a simple model of human physiological regulatory response. ASHRAE Trans., 77(1):247–262.
  • Höppe, P. (1984). Die Energiebilanz des Menschen: In: Münchener Universitätsschriften- Fachbereich Physik, Wissenschaftliche Mitteilungen Nr. 49. Meteorologisches Institut, Universität München, München.
  • Höppe, P. (1999): The physiological equivalent temperature – a universal index for the biometeorological assessment of the thermal environment. - International Journal of Biometeorology 43, 71-75.
  • VDI (2008): VDI 3787. Environmental meteorology. Methods for the human biometeorological evaluation of climate and air quality for urban and regional planning at regional level. Part I: Climate, Blatt 2/ Part 2
This website uses cookies. By using the website, you agree with storing cookies on your computer. Also you acknowledge that you have read and understand our Privacy Policy. If you do not agree leave the website.More information about cookies