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Thermal comfort is a concept that is tied to an individual's satisfaction with his or her indoor environment. For a person to feel thermal comfort, he must be neither too cold or too hot. Since this type of comfort can be affected by both internal and external factors, not every person will be comfortable in the same environment. The three main external factors are humidity levels, air temperatures, and air movements. These factors are often closely monitored in work environments, since employees are typically more productive if they are not too hot or cold.
Many different factors can contribute to thermal comfort, and each individual can have a different range of temperatures he or she is satisfied with. Internal factors, such as metabolism and age, can contribute to individual thermal sensitivity, and gender differences have also been noted. There can also be a psychological component in some cases. The amount and type of clothing a person wears also affects his comfort level, as someone wearing heavy clothing in an indoor environment will tend to be warmer than another person wearing light clothes.
Employers often attempt to provide a level of thermal comfort that is likely to satisfy the largest number of people. In order to achieve this, various heating, ventilation, and air conditioning (HVAC) systems can be used. The three external factors that can be controlled in this manner are temperature, humidity levels, and air circulation. Temperature is the core factor behind thermal comfort, though it can be impacted significantly by both humidity and air velocity.
Some air movement in indoor environments is typically necessary, though excessive levels can cause a room to feel colder than it is. Indoor air velocities higher than 0.25 meters per second (50 feet per minute) can also be a distraction to workers. High humidity can make people feel uncomfortable and often results in an area feeling stuffy, but low humidity levels can cause respiratory problems. All of these factors must be balanced in order to provide the largest amount of comfort to the most people.
In addition to human employees, many of these concepts have also been applied to livestock. Thermal comfort in animals can affect productivity, and studies have shown a reduction in certain biological functions in the presence of extreme temperatures. Sheep in particular have shown a reduced ability to digest food when in a state of thermal discomfort, so addressing this issue may lead to higher yields.