About thermal comfort index

Thermal comfort is defined by the thermal balance between a human body and the environment. It depends on several meteorological and non-meteorological factors. Non-meteorological thermal comfort factors, such as activity and clothing, can be influenced by human to a greater or smaller degree. However, the impacts of the atmosphere where we live cannot be changed. Therefore special attention has to be paid to the meteorological factors that define thermal comfort.

In addition to temperature, which certainly has a very important and sometimes a crucial role, the sensation of comfort is also affected by the wind, humidity, solar and terrestrial radiation. Airflow enhances heat removal from the body surface. That is why wind in the summer can alleviate the feeling of heat and in the winter it can enhance the feeling of cold. Sweating is one of the very effective ways of protecting the body from overheating. During evaporating sweat from the skin surface heat is consumed and it cools body. However, amount of moisture in the air defines how much evaporated moisture from the body can be absorbed in the air. If the air is very humid, evaporation of the sweat will be difficult. This is why high temperatures and high humidity during summer are very unpleasant and people can feel sultriness.

Here is used combined biometeorological index to evaluate so called thermal comfort index. It is calculated from outdoor temperature, relative humidity and wind speed. The index is classified into nine categories: from very cold trough the pleasant to the very hot. In the table there is also recommended clothes for each index that is suitable to protect human body from the unpleasant atmospheric influences.

Recommendations refer to the circumstances in the shadow (we are not directly exposed to the Sun) and we are not sitting but walking with velocity 3.2 km per hour, that is considered as an easy walk.

Daily course of thermal comfort for the current and next two days is presented on the graph. Thermal comfort forecast is based on meteorological data issued by mesoscale forecast model ALADIN.