THERMAL COMFORT

The issue of thermal comfort and the general climate of a building depends on the human factor. 

Thus, in the evaluation of the optimal indoor climate, and particularly with regard to comfort conditions, the criteria which is influencing it are mostly subjective. Any study about indoor environment of a building must take into account the users who each perceive the limits of thermal comfort differently.

According to the American Society of Heating, Refrigerating and Air Conditioning (ASHRAE), thermal comfort is defined as the state of mind in which a person does not desire any thermal change in the indoor environment and expresses satisfaction with the prevailing conditions.

It is obvious that the state in which the user feels thermally comfortable has a subjective character, because in the same environment one person may express satisfaction with the prevailing thermal conditions, while another person, with the same conditions, may express dissatisfaction.

In order to give the state of thermal comfort an objective character through scientific evaluation, a number of parameters have been defined which influence it, namely the following:

1.Physical parameters

• Air temperature (°C)
• Average radiant temperature of indoor surfaces (°C)
• Air humidity and relative humidity (Pa)
• Indoor air velocity (m/s)
• Spatial distribution of the above parameters

2. Biological parameters

• The gender of the users of the space
• The age of the occupants of the premises
• The habits of the occupants of the premises

3. External parameters

• The type of activities of the site users
• The type of clothing worn by the users of the premises

Based on the theory of thermal comfort, many organizations have issued guidelines and regulations about permissible levels of temperature and relative humidity values. In our country, the Technical Chamber of Greece (TEE) with its technical directive 2425/86, proposes the values shown in the following table as recommended design conditions for air-conditioned rooms.