The term ‘Thermal Comfort’ describes a person’s state of mind in terms of whether they feel too hot or too cold.
Environmental factors (such as humidity and sources of heat in the workplace) combine with personal factors (ie your clothing) and work-related factors (how physically demanding your work is) to influence your ‘thermal comfort’.
Thermal comfort is very difficult to define and requires an understanding of a range of environmental, work-related and personal factors when deciding what makes a comfortable workplace temperature.
Within the built environment, the realistic aim of the Heating, Ventilation and Air-Conditioning (HVAC) systems is to achieve a thermal environment that satisfies the majority of people in the workplace. Thermal comfort is not measured by room temperature, but by the number of employees complaining of thermal discomfort.
By managing thermal comfort, you are likely to improve the occupant’s sense of wellbeing, morale and productivity as well as improving health and safety. People working in uncomfortably hot and cold environments are more likely to behave unsafely because their ability to make decisions and/or perform manual tasks deteriorates. For example:
Generally building occupants adapt their behaviour to cope with their thermal environment, eg adding or removing clothing, unconscious changes in posture, choice of heating, moving to or away from cooling/heat sources etc.
The problems arise when this choice (to remove a jacket, or move away from heat source) is removed, and people are no longer able to adapt. In some instances, the built environment within which people work is a product of the processes of the job they are doing, so they are unable to adapt to their environment leading to a decrease in the sense of wellbeing.
The human body will generate excess heat into the environment so that the body can continue to operate. The heat transfer is proportional to any given temperature difference. In cold environments, the body loses more heat to the environment and in hot environments the body does not exert enough heat. Both the hot and cold scenarios lead to discomfort.
Within the built environment, most building occupants will feel comfortable with a room temperature in the range of 20 to 22°C but this may vary greatly between individuals and depending on factors such as activity level, clothing, and humidity.
Thermal neutrality is maintained when the heat generated by the human metabolism can dissipate, thus maintaining thermal equilibrium with the surroundings. The main factors that influence thermal comfort are those that determine the heat gains and heat losses - namely metabolic rate, clothing insulation, air temperature, mean radiant temperature, air speed and relative humidity. Psychological parameters, such as individual expectations, also affect thermal comfort.
There are six primary factors that directly affect thermal comfort that can be grouped in two categories: personal factors - because they are characteristics of the occupants and environmental factors - which are conditions of the thermal environment.
Even if all these factors vary with time, standards and HVAC design criteria usually refer to a steady state to study thermal comfort, just allowing limited temperature variations.