Perceived temperature

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The perceived temperature is understood as the perceived ambient temperature, which can differ from the measured air temperature due to various factors . It is a bioclimatic measure of the thermal well-being and includes the spectrum from the heat - or heat sensation on comfort to feeling cold . In mammals and birds with constant body temperatures , perceived cold can be accompanied by tremors , depending on their conditioning .

The perceived temperature can be defined quantitatively as the temperature that would have to prevail in a certain standard environment in order to experience an identical temperature sensation. Wind chill, for example, especially at temperatures well below body temperature, lowers the perceived temperature, high humidity in hot ( humid conditions) increases it.

Test results on humans are about the perceived temperature according to VDI 3787, for higher temperatures the heat index of the American Meteorological Society combined with the air humidity , further parameters are summarized by the Climate Michel model of the German Meteorological Service .

Influences on the heat balance of humans

Humans give off a certain amount of heat to the environment over time. For an average, lightly clad person, for office work in an average office at 20 degrees Celsius, around 46% through thermal radiation , 33% through convection , around 19% through evaporation on the skin and 2% through breathing . The most important factors influencing the heat balance in this case are the temperature difference between the air and the body surface, the size of the body surface itself, its thermal properties and the degree of radiation exposure from outside. An experimental study on naked people between 23 and 35 degrees Celsius comes to a maximum value of 70% of the heat output via radiation, which decreases to 0% at 35 degrees.

If the person stands in the wind, their body is cooled down or heated up proportionally to the wind speed. The effect of the wind speed is described by the wind chill . It is a convective heat transfer. The perceived temperature of the Windchill differs from the measured temperature.

Felt temperature in red

However, a variety of other factors play a role. The influence of air humidity is measurable and therefore comparatively easy to calculate . The corresponding compensation value is called humidex , the decisive influencing effect is the sultriness . In simple terms, one can state here: if more energy is withdrawn from the body than it produces, we perceive it as cold , if high temperatures prevail with low humidity, if this is perceived as dry heat (especially in direct sunlight), its ability to thermoregulate is through If the humidity is limited, this is perceived as humid.

Other influencing factors are the level of activity of the person, their height and weight, clothing, exposure to the sun (degree of shade, position of the sun) and various skin properties ( skin moisture , insulating creams, beard growth, etc.). However, this list is not complete and could, for example, be expanded to include factors such as clothing color, as this has an influence on the absorption or reflection properties of clothing. In general, all factors that have an influence on the body's thermoregulation and / or the thermal properties of the body's surface and the heat transfer between the organism and the environment are also of importance for the perceived temperature.

Thermal sensation

A person's wellbeing is primarily determined by the activity of the body's own thermoregulation. The more heat you have to produce in order not to cool down, and the more you have to sweat to avoid overheating, the more uncomfortable we feel. The thermoregulation is closely linked to the blood circulation and every adjustment of the body temperature demands it, either in the form of cold stress or a heat load . People with circulatory problems are therefore particularly sensitive to temperature.

The sensation of cold and, in the opposite case, of heat is also subjective. For a resident of the tropics, 10 ° C is quite cool, while an Eskimo would find this temperature rather moderate. However, this also applies to an individual, and so the physiological and even psychological state of a person affects their temperature perception.

According to VDI guideline 3787 Part 2, a perceived temperature is in turn contrasted with a physiological evaluation of the temperature perception (see table below). One assumes the activity of faster walking and clothing that is well adapted to the respective temperature conditions.

Perceived temperature and thermal stress according to VDI 3787 Part 2
Perceived temperature
in degrees Celsius
Thermal sensation Thermophysiological
stress
below −39 very cold extreme cold stress
−39 to −26 cold severe cold stress
−26 to −13 cool moderate cold stress
−13 to 0 slightly cool weak cold stress
0 to 20 comfortable Well-being possible
20 to 26 slightly warm weak heat load
26 to 32 warm moderate heat load
32 to 38 hot strong heat load
over 38 very hot extreme heat load
serves as a line break, please do not remove it

The German Meteorological Service uses the Climate Michel model for its calculation of the perceived temperature and assumes a man (the Michel) with a height of 1.75 m, a body weight of 75 kg, a body surface of 1.9 m² and one Age from about 35 years.

literature

  • VDI, 1998: Methods for the human-biometeorological assessment of climate and air hygiene for urban and regional planning. Part I: Climate. VDI guideline 3787 part 2.

Web links

Individual evidence

  1. Rassabséwindé Désiré Compaore: contribution to climate righteous Building in Burkina Faso using the example of office buildings. In: Dissertation. See Appendix 2 , accessed on January 12, 2017 .
  2. E. Specht: Man as a thermal system. Retrieved January 12, 2017 .
  3. James D. Hardy and Eugene F. DuBois: Regulation of Heat Loss from the Human Body . In: Proceedings of the National Academy of Sciences . tape 23 , no. 12 , 1937, pp. 624-631 ( pnas.org ).