Thermal comfort parameters

Many subjective perceptions determine living comfort, even the colour of the surroundings plays a certain role – particularly for the mood of person who thereby expresses his or her perceptions. Living comfort mainly depends on the “thermal comfort”. This has been well-researched and the results have been incorporated into international standards (DIN ISO 7730). A large part of the information available to us today is due to the work of the Danish scientist P. O. Fanger (Wikipedia Seite).

Optimal thermal comfort is established when the heat released by the human body is in equilibrium with its heat production. Fanger's comfort equation is derived from this fact. It creates a relationship between the activity (e.g. sleeping, running…) and clothing as well as the determining factors for the thermal surroundings, which are as follows:

• air temperature
• the temperature of the surrounding surfaces, this can also be summarised as the “radiant temperature”,
• air speed and turbulence
• air humidity.
  

There is a complete range of combinations of these four comfort factors where the level of comfort is very good, this is known as the comfort range. It can be determined by Fanger’s equation, documented in ISO 7730. Furthermore, according to this standard it is essential that

• the sultriness limit in relation to the air humidity is not exceeded,
• air speeds are within closely defined limits (for speeds under 0.08 m/s, the number of dissatisfied due to draughts is less than 6%)
• the difference between radiant temperature and air temperature remains small,
• the difference in the radiant temperature in various directions remains small (less than 5 °C, known as the “radiation temperature asymmetry”),
• the indoor air temperature stratification is less than 2 °C between the head and ankles of a seated person,
• the perceived temperatures in the room change by no more than 0.8 °C at different locations.

Regarding the last point, P.O. Fanger writes: “the more irregular the thermal field in a room is, the greater the expected number of dissatisfied people.”

Air stratification: The temperature stratification of the air is imper- ceptible in a room that has Passive House windows. If this room is heated by means of a radiator (note: in a Passive House, heating is possible by means of supply air as well as with all other methods), the heater can be placed anywhere in the room, for example, it can also be positioned next to the interior wall – and optimum thermal comfort can still be achieved in accordance with the ASHRAE comfort category “A”. (Calculation: J. Schnieders, PHI).