Environment, Temperature, Thermodynamics

What is thermal perception?

Taking requests, will be explained in this post what is thermal perception, also known as apparent temperature.

Definition and calculation

Thermal perception is the temperature “felt” by the body, in addition to air temperature, considerate wind speed, humidity and density of air. This is the thermal perception equation considering wind speed.


Where TP is the thermal perception, s is the wind speed and T is the official temperature.

There is another way to calculate the apparent temperature, with Heat Index and Wind Chill. The following equation calculate the Heat Index, which considerate the relative air humidity (h) in percentage and air temperature (t) in Fahrenheit (ºF), when greater the Heat Index, bigger is the heat perception. This equation was obtained by mathematical method Multiple Regression Analyzes.

This is the table which relates the temperature in Fahrenheit with air humidity.

Another equation calculates the apparent temperature considering the wind chill.

T_{wc}=13,12+0,6215\cdot T_{a}-11,37\cdot V^{0,16}+0,3965\cdot V^{0,16}

Where T is the temperature in Celsius and V is the wind speed in km/h.

The heat index equation is used when the air temperature stays equal or higher than 80ºF or 22,7ºC, while the Wind Chill is used when the temperature stays equal or below 45ºF ou 7ºC. Both are calculated in Celsius or Fahrenheit degree. 

Influence of factors

  • Bigger air humidity (quantity of steam), higher the thermal perception;
  • Higher wind speed, decrease apparent temperature;
  • Some people are more adapted to cold, others to heat, therefore, personal preference influences too.

Fahrenheit, Celsius and Kelvin

The Celsius temperature (ºC) is counted from the freezing of water, which is the zero degree. The Fahrenheit (ºF) has as zero point the freezing of mixture of water with ammonium chloride and 100 as the average temperature of human body. This is the relation between the two scales.

Tf=\frac{9}{5}\cdot Tc+32

Tf is the temperature in Fahrenheit and Tc in Celsius. The Kelvin scale (ºK) has the stopped molecules as zero point. To convert from Celsius to Kelvin, just add with 273,15.


About Pedro Ney Stroski

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