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Thermal Comfort

ASHRAE Standard 55: “Thermal comfort is the condition of mind that expresses satisfaction with the thermal environment”.

Although this definition is not very precise, it emphasizes the fact that a lot of parameters may be involved in order to achieve proper thermal conditions.

ASHRAE Fundamentals (2001): “in general comfort occurs when body temperatures are held within narrow ranges, skin moisture is low and the psychological effort of regulation is minimized”.

It is important to understand basic principals of the thermal interaction between the human body and the environment before studying the parameters that influence the thermal comfort.


Conditions of thermal comfort

Thermal sensation is the most important parameter in the perception of comfort. Air is the primary transport mechanism for thermal comfort while air speed and turbulence influences the sensation of cooling and draughts. High infiltration or unnecessary air change rates result in the loss of conditioned air and may prevent comfort conditions from being attained (AIVC).

The factors that influence the thermal comfort are divided to primary and secondary ones:

  • Primary Factors
    • Temperature and radiation (dry bulb, mean radiant)
    • Operative and resultant temperatures
    • Relative humidity
    • Air speed and turbulence
    • Clothing
    • Perception of thermal comfort

other parameters such as state of health, level of physical activity, gender, working environment and individual preferences also influence perception of thermal comfort.

  • Secundary Factors
    • Nonuniformity of the environment
    • Age
    • Sex
    • Adaption
    • Seasonal and Circadian Rhythms