Because people in developed countries spend about 90% of their time indoors, their sense of warmth becomes one key comfort factor for interior spaces. VTT Technical Research Centre of Finland has developed a new method for assessing the individual thermal comfort experienced by different user groups. The design of energy efficient buildings -- such as day care centres, schools, offices and homes for the elderly -- should pay more attention in future to the thermal comfort of user groups according to real needs.
The new method developed for assessing thermal comfort (Human Thermal Model, HTM) is based on modelling of individual anatomy and physiology. The method can be used to assess the impact of individual characteristics -- gender, age, body mass index and muscularity -- on the volumes of various tissue types (bone, muscle, fat and skin).
The heat and moisture transfer between a person's anatomy, clothing and the environment determine the local temperature of body tissues. These temperature values can be used to calculate the local thermal comfort of different parts of the body.
An adequately precise identification of the various body tissues is important because muscle tissue, for example, when at rest produces heat at a basal metabolic rate of 0.67 W/kg, while the heat produced by fat tissue is at a rate of 0.004 W/kg. Light office work produces just over 2W of thermal power per kilo of muscle, while cleaning work produces 5W and strenuous sporting performance momentarily over 20W.
When comparing the thermal comfort of women and men using same values for all other individual characteristics (body mass and muscle indexes), the indexes for male thermal comfort were on average 0.39 units higher than for women in the case of 20-year-olds and 80-year-olds, and 0.48 units higher for 50-year-olds.
Several previous researches have shown men to have statistically more muscle tissue on average than women. People also lose muscle mass as they grow older. Because the thermal output of muscle tissue per kilogram is several orders of magnitude higher than that of fat tissue, it is important to be aware about individual amount of muscle tissue. Thus gender and individual muscularity in particular out of the various characteristics have a considerable impact on metabolic rate and tissue temperature -- and in the end on the person's thermal comfort.
One mega trend in the coming years will be continuous improvement in the energy efficiency of existing and new construction. From occupant point of view it will important to be able to estimate thermal comfort of different end user groups, so that relevant design and maintenance solutions would ensure simultaneous fulfillment of both energy efficiency and satisfaction with thermal conditions.
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