Thermal Comfort

THERMAL COMFORT

Thermal comfort describes the human satisfactory view of the thermal environment. It refers to a number of conditions in which the majority of people feel comfortable.

Thermal comfort is rated amongst the most important conditions for improving comfort and satisfaction of occupants with their indoor environment.

Factors influencing thermal indoor environment

The heat exchange between the human body and its environment occurs mainly in three ways, namely through: (Fig. 1.20)

 • Radiation

• Convection

• Evaporation

Thermal indoor environment is affected by both internal and external sources.

Common heat sources:

• electrical equipment (such as lighting and computers)

• sun radiation

• human presence

Common sources of cold:

• window surfaces

• poorly insulated walls

•  thermal bridges in the constructions

All these sources will influence the human perception of the environment and therefore the comfort level. (Fig. 1.21)

Thermal comfort refers to the perceived feeling on the human body as a result of the effect of heat and cold sources in the environment.

Factors that influence thermal comfort

Thermal comfort is mainly influenced by six variable factors which are needed to maintain a healthy balance in order to sustain the occupants' satisfaction with their surrounding environment.

Air temperature, a common component of thermal comfort; it can easily be influenced with passive and mechanical heating and cooling.

Mean radiant temperature, the weighted average temperature of all exposed surfaces in a room.

Air velocity (or air flow) quantifies the speed and direction of the air movements in the room. Rapid air velocity fluctuations might result in draught complaints.

Humidity (or relative humidity) is the moisture content of the air. Too high or too low humidity levels may induce discomfort.

Clothing level, the amount of insulation added to the human body. Higher clothing levels will reduce the heat lost through the skin and lower the environments temperature perceived as comfortable.

Physical activity level (also called metabolic heat) has an influence on the amount of heat produced by the human body and therefore also in the perception of a hot or cold environment.

Average comfort rating

• Combining all the factors mentioned above, an average comfort rating can be predicted. However, in some cases it can be impossible to reach a thermal environment that satisfies all the occupants of a building because of their individual preferences. (Fig. 1.22)

In those cases, it's still possible to specify conditions that are likely to be perceived as acceptable to most. And if combined with opportunities for individual control (such as bezo change of clothing or window opening), the overall satisfaction with the environment will increase considerably.

Thermal comfort affects the work performance

Thermal conditions can affect the building occupants' productivity and work performance through several mechanisms. Thermal discomfort can:

• cause attention distraction

• disturb well –being (Heat strokes, Heart diseases, Dehydration, Cold – Frostbite)

• reduce the ability to concentrate properly (Decreases both mental and physical performance)