Essentially, comfort is expressed by the satisfaction of a building’s occupants. Therefore, the most appropriate way to measure comfort is to ask occupants if they feel comfortable. The EN-ISO 7730 (ISO, 1993) standard scale is most frequently used to determine this. When there are several people in a room, the mean vote is calculated. Fanger (1982) proposed a method for calculating the mean vote of a group of people from air parameters (temperature, humidity and air velocity), clothing and activity. He called this the ‘predicted mean vote’ (PMV). Fanger also suggested that the percentage of dissatisfied people is related to mean vote. It should be noted that, according to this model, it is impossible to satisfy everybody: the minimum number of dissatisfied people is approximately 5 per cent. Fanger (1982) also published a relationship between the physical parameters that influence thermal comfort and the mean vote, which can then
be predicted. The Fanger equation of comfort is now accepted all over the world. The solution of the Fanger equation is iterative; therefore, for all practical purposes, a computer is essential. International Standard EN/ISO 7730
provides a simple program in BASIC.
For example, a sitting person wearing a lounge suit would prefer, on average, an operative temperature of 22°C ± 2°C. If this person is more active – for example, when giving a lecture – a temperature of 18°C ± 3°C is preferred. This is why a temperature of about 20°C is preferred in schools and offices. A sitting person wearing shorts and a light shirt will prefer 26°C ± 1.5°C, while an average person naked and at rest is comfortable, on average, at 28°C ±1°C.
The Fanger equation is valid within the following domain:
• metabolism from 46 to 232 watts per square metre body area (W/m2) (0.8
to 4 units of metabolism (met));
• clothing from 0 to 2 units of thermal resistance of clothing (clo) (or
clothing thermal resistance from 0 to 0.310 (m2K/W));
• air temperature between 10 and 30°C;
• mean radiant temperature from 10 to 40°C;
• relative air velocity less than 1 m/s;
• water vapour partial pressure between 0 and 2700Pa.
The practical consequence for administrative buildings and dwellings, where the activity is close to 1.1 met, is that the optimal operative temperature in winter (about 1 clo) is between 20 and 24°C, while in summer, with lighter clothing, the optimal operative temperature is between 23 and 26°C.