Environmental comfort is defined as the particular condition of psychophysical well-being determined by air temperature, humidity and the levels of noise and light in an enclosed environment.
From this definition, we can distinguish between thermal-hygrometric comfort, acoustic comfort and visual (lighting) comfort.
Environmental comfort is a subjective sensation, depending on individual sensory perception and closely linked to psychological, cultural and social aspects. It is also a function of time and of the person’s ability to adapt, as well as of sex, age and health status. For this reason, it is a complex parameter to quantify analytically: being subjective, it can only be quantified in statistical terms.
Thermal comfort is defined by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) as that state of mind which expresses satisfaction with the thermal environment.
According to studies on the topic, thermal comfort in a building is achieved through the interaction of subjective variables and environmental variables.
The subjective variables relate mainly to clothing and to the activity carried out by the individual within the space, which affects the person’s metabolic rate and results in heat and moisture being released to the surrounding environment.
The environmental variables are as follows:
Air temperature
Indoor relative humidity: this is the ratio between the amount of water vapour contained in a given mass of air and the maximum amount that the same mass of air could contain at the same temperature and pressure.
At typical comfort temperatures, humidity has only a modest effect on perceived comfort as long as it does not become extremely high or extremely low. At higher temperatures, evaporative cooling becomes the main mechanism for dissipating body heat, and very humid air (relative humidity close to 100%) prevents sweat from evaporating effectively. At the opposite extreme, when relative humidity drops below about 20%, the mucous membranes tend to dry out and susceptibility to infections increases. At low temperatures, very dry air can increase the sensation of cold because moisture that reaches the skin surface evaporates, producing an additional cooling effect.
Mean radiant temperature:
This is the weighted average temperature of the surfaces surrounding the space, including the effect of incident solar radiation, and it influences radiant heat exchange. Together with air temperature, mean radiant temperature is one of the main factors affecting thermal sensation, because radiant heat falling on the skin activates the same receptors involved in perceiving temperature. If the body is exposed to cold surfaces, a significant amount of heat is radiated towards them, producing a sensation of cold.
Air velocity:
Air movement can produce thermal effects even without changes in air temperature and can enhance heat dissipation through the skin in two main ways:
1) by increasing convective heat transfer as long as air temperature remains lower than skin temperature;
2) by accelerating evaporation of moisture from the skin, thus providing physiological cooling. At very high humidity evaporation is limited and air movement has little cooling effect; at moderate humidity levels, however, air movement helps to remove the saturated air layer close to the skin and promotes continuous evaporation.
In practice, achieving good indoor air quality and comfort means combining appropriate building design, correctly sized and controlled ventilation systems, high-efficiency filtration and a regular maintenance plan. When these elements work together – supported by reliable filters and components – indoor spaces become healthier, more comfortable and more energy efficient for the people who live and work in them.