This simple infographic explains the six primary factors affecting human thermal comfort. Thermal comfort is defined as a person’s state of mind regarding whether they feel too hot or too cold, which is achieved when the body can maintain a stable internal temperature.

These factors relate to the conditions of the surrounding environment:

Environmental Factors

• Air Temperature:The temperature of the air surrounding the body, typically measured with a standard thermometer.
• Radiant Temperature:This refers to the mean radiant temperature, which is the average temperature experienced across all surfaces in a room (walls, ceiling, floor, furniture, etc.) regardless of air temperature.
• Air Speed:The rate of air movement across a person. Moving air can increase heat loss through convection, which is why a fan can make you feel cooler even if the air temperature remains the same.
• Relative Humidity:The amount of moisture in the air. High humidity prevents sweat from evaporating from the skin, which is the body’s main way of cooling down in hot environments.

The image also highlights that infrared radiation has a fast and positive effect on thermal comfort, while convective heating alone primarily impacts air temperature.

Understanding these environmental factors is essential for designing comfortable indoor environments and HVAC (heating, ventilation, and air conditioning) systems.

By managing all of these variables rather than just air temperature a person is able to feel more ‘comfortable’ at a lower set temperature, in most cases up to 5c less, thus saving energy (each 1c reduction equates to around 10% energy savings).

In addition as the surfaces act as ‘emitters’ going on to warm the air, the humidity remains constant and condensation is managed effectively.