What is Thermal Comfort?

Carlos Gali Photography

Human thermal comfort describes the state of mind that expresses satisfaction with the surrounding environment and refers to several conditions in which the majority of people feel comfortable.

The human body produces heat depending on the level of activity, and expels heat according to the surrounding environmental conditions.

The body loses heat in three main ways:  radiation, convection and evaporation. An unpleasant sensation of being too hot or too cold (thermal discomfort) can distract people from their activities and disturb their well being. This may reduce the ability to concentrate and decrease motivation to work. Thermal comfort is affected by six variable factors which are needed to maintain a healthy balance in order to sustain satisfaction with the surrounding environment.

1) Air Temperature is the most common measure of thermal comfort and can easily be influenced with passive and mechanical heating and cooling.

2) Mean Radiant Temperature is the weighted average temperature of all exposed surfaces in a room. The greater the difference between air temperature and exposed surfaces, the greater the Relative Air Velocity.

3) Relative Air Velocity (‘wind chill factor’) is the apparent temperature felt on exposed skin due to wind.  For example, if cold air is leaking in from a window, the air temperature feels lower than the actual air temperature, hence the increased likelihood of feeling cold, even when the heater is on.

4) Humidity or relative humidity is the moisture content of the air. If the humidity is above 70% or below 30% it may cause discomfort.

5) Activity Levels can reduce the heating needs, as lower air temperature is acceptable when occupants have higher activity levels.

6) Thermal Resistance of clothing or warm blankets in a bedroom can reduce the need of heating.

Building design is affected by the first four of these thermal comfort variables. The last two depend on the action and behaviour of the occupants.

Do you want to know more about thermal comfort? Then have a read through our article what factors are influencing thermal comfort.