Thermal comfort of a place is determined by environmental factors such as the air temperature, humidity, air velocity and radiant temperature. But personal factors such as physical characteristics of a person, the clothes he is wearing, his metabolic rate, etc. are also important determinants of thermal stress or comfort.
Air temperature which is normally given in degree Celsius is the most primary thing influencing the level of thermal comfort. But humidity also plays a big role. Humidity is referred by the term relative humidity of a place which is the ratio of the amount of evaporated water contained in the air and the maximum amount of water that the air in a particular temperature can hold.
When the air is too humid (for example, whenever the relative humidity is more than 70%), the sweat produced in our body cannot evaporate quickly since the surrounding air is already enough saturated with water vapor. Another determining factor is the radiant heat source. In fact, this may often play a greater role than air temperature in deciding the thermal comfort level of a person. Close proximity with any radiant heat source such as sun, fire or other objects that emit heat (kiln walls, ovens, electric fire, molten metal) will increase heat stress.
When discussing thermal or heat comfort, we also need to take into account the air velocity. Air velocity refers to the speed of the surrounding air in a place. If the air can circulate freely at a good speed and if it is cooler than the air outside, this will result in heat reduction. On the contrary, if the air inside a place (especially an artificially heated place) is stagnant or still, this will create stuffiness and will affect thermal comfort.
Apart from these factors, personal effects also play a part. For example, what kind of clothes you are wearing. Clothes that provide ample insulation will keep you comfortable both in warm and cold weather. However, if you are working at a job where you need to wear uniform or personal protective gear which is not insulation-friendly, this will lead to heat stress and thermal discomfort.
For more on the subject and for other articles explaining how to keep your heating and cooling systems running efficiently, please follow our next posts on this blog.