Environmental Factors: Thermal Environment

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1. Introduction Thermal comfort is the condition of mind that expresses satisfaction with the thermal environment and is assessed by subjective evaluation (ANSI/ASHREE Standard 55). There are six primary factors that directly affect thermal comfort that can be grouped in two categories namely personal factors and environmental factors. The personal factors are metabolic rate and clothing level, the environmental factors are air temperature, mean radiant temperature, air speed and humidity. The metabolic rate is decided by the human activity level and the heat loss from the body is decided by the clothing insulation value, the speed of body movement, openings in clothing and climatic conditions. The amount of thermal insulation of clothing worn by a person has a substantial impact on thermal comfort, because it influences the heat loss and consequently the thermal balance. Layers of insulating clothing prevent heat loss and can either help keep a person warm or lead to overheating. Generally, thicker the clothing greater is its insulating ability and water vapour resistance. Higher wind speeds can decrease the insulating ability of the material .Higher vapor pressure gradient between the skin and the ambient air can decrease the insulating ability of the material (Havenith, 1999). 1 clo is equal to 0.155 m²•K/W (0.88 °F•ft²•h/Btu). This corresponds to trousers, a long sleeved shirt, and a jacket. (ANSI/ASHREE Standard 55) The human body tries to maintain the core

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