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The Effect of Thermal Insulation of Clothing on Human Thermal Comfort

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The Effect of Thermal Insulation of Clothing on Human Thermal Comfort R. Tuğrul Oğulata The Effect of Thermal Insulation Department of Textile Engineering, Faculty of Engineering and Architecture, Cukurova University, of Clothing on Human Thermal Comfort Adana 01330, Turkey Abstract The human body is under various continuous external conditions, some of which make wearers uncomfortable. Usually, human thermal comfort depends on combinations of clothing, climate, and physical activity. Specifically thermal insulation in clothing is an important parameter of thermal comfort. Therefore, this paper discusses theoretically the basic physical principles of the body’s mechanism for heat transfer with the environment. In this study, the body’s heat balance was examined, and the effects of clothes and various climatic conditions on thermal comfort were investigated for different physical activities. Key words: clothing insulation, thermal comfort, physical activity, climatic conditions. On the other hand, the body continuously theoretically the general, material de- n Designations produces heat, which must be transferred pendencies between heat generation by Ab area of body surface, m2 to the environment. People sometimes humans and their heat losses considering AD area of body surface, m2 feel uncomfortable as a result of some of various types of activity under different C heat loss by convection, W/m2 their physical activities due to the change conditions, on the bases of well-known Ck heat loss by thermal conduction, W/m2 of external conditions. laws and equations, as well as of avail- Cres sensible heat loss due to respira- able experimental data concerning ther- tion, W/m2 The temperature and humidity of the en- mal property values. Eres evaporative heat loss due to respi- vironment may profoundly influence the ration, W/m2 body’s skin and interior temperature [22]. In the study, the role of clothing in the Esk heat loss by evaporation from the The human body is adapted to function thermal balance of the human body and skin, W/m2 within a narrow temperature range. Gen- thermal comfort under steady-state con- fcl clothing area factor, clo erally, the human body keeps its body ditions have thus been investigated for Fvf viev factor between body and surr- temperature constant at 37 ± 0.5 °C un- various climatic conditions and different ounding der different climatic conditions. physical activities. h body height, m hc coefficient of convection heat Human thermal comfort depends on transfer, W/m2K combinations of clothing, climate, and Heat exchanges of human body with environment Icl thermal insulation of clothing, clo physical activity [13]. The human body Icli individual resistances of various converts the chemical energy of its food The body converts the chemical energy garment, clo into work and heat. The amount of heat of its food into work and heat, produc- M metabolic rate (internal energy generated and lost varies markedly with ing through its processes of metabolism production), W/m2 activity and clothing levels [19]. a great deal of heat. The amount of heat Pa partial vapour pressure, Pa produced depends on the degree of activ- Ps saturation pressure of water vapor, The heat produced is transferred from ity [9]. The living body continuously pro- Pa the body’s skin to the environment. In a duces heat which must be transferred to R heat loss by thermal radiation, W/m2 steady-state heat balance, the heat energy the environment. The expulsion of body Rcl insulation of clothing, m2K/W produced by the metabolism equals the heat primarily occurs from the body’s Ta ambient air temperaure, °C rate of heat transferred from the body surface. Through blood circulation, heat Tcl clothing surafce temperaure, °C by conduction, convection, radiation, is transported to the skin, from which it is Tr radiant temperaure, °C evaporation and respiration [17]. transferred to the environment [22]. Tsk skin temperaure, °C Va air velocity, m/s Therefore, clothing is needed to protect In a steady-state heat balance, the heat w body weight, kg the body against climatic influence and energy produced by metabolism equals W external work, W/m2 to assist its own thermal control func- the rate of heat transferred from the body RH relative humidity, % tions under various combinations of by conduction, convection, radiation εcl emmisivity of clothing environmental conditions and physical evaporation and respiration [17]. σ Stefan-Boltzmann constant, W/m2K4. activities [13]. The fundamental thermodynamic proc- n The heat loss from the body and the feel- ess in heat exchange between man and Introduction ing of individual comfort in a given envi- his environment may be described by The human body is affected by various ronment is much affected by the clothing the general heat balance equation (for the external conditions in the winter and worn [15]. However, of the copious per-unit body surface area) [1, 4, 8, 10]. summer seasons. These external condi- research work carried out considering M - W = C + R + E + tions can include changes in ambient different aspects of human thermal in- sk (1) + (C + E ) + C temperature, vapour pressure, air veloc- sulation by clothing, elaborations which res res k ity, and clothing insulation, among other generalise this problem have been very The external work (W) in the equation factors that affect skin temperature [21]. rare. The aim of this study was to analyse is small, and is generally ignored under FIBRES & TEXTILES in Eastern Europe April / June 2007, Vol. 15, No. 2 (61) 67 most situations. The internal energy pro- Convection The thermal resistances proposed for duction (metabolic rate) is determined by The convection heat transfer from the individual items are listed in Table 3, to metabolic activity. Table 1 shows the rate human body to the environment is given be combined by means of the following of body heat production for an average [4, 8, 6]. Equations (6) or (7) [11, 5]: male for different types of activity [4]. C = fcl hc (Tcl - Ta) (3) clo-value (men) = 0.727 Icli + 0.113 (6) Table 1. Typical metabolic heat generation The heat transfer coefficient hc depends clo-value (women) = 0.770 Icli + 0.050 (7) for various activites [4]. on the air velocity across the body, and consequently also upon the position of Heat The human body is insulated against heat Activity generation, the person and orientation to the air curr- gains or losses by clothing. The insula- W/m2 ent [17]. An approximate value of h dur- c tion of clothing is often expressed in clo ing forced convection can be evaluated Resting units, but it is used in SI units (Rcl) in Sleeping 40 from the definition given in [1] as Reclining 45 calculations. The relationship between . 0.5 Seated, quiet 60 hc = 12.1 Va (4) Rcl and Icl is Standing, relaxed 70 R = 0.155 I (8) where Va is the air velocity. The cloth- cl cl Walking (on the level) ing area factor (fcl) in Equation (3) is 0,89 m/s 115 Radiation 1,34 m/s 150 expressed as follows [2]: 1,79 m/s 220 The rate of heat transfer by radiation fcl = 1.05 + 0.1 Icl (5) depends on the mean temperature of Office activities surrounding surfaces, skin or cloth- Reading 55 where Icl is the thermal insulation of Writing 60 clothing. Values of thermal insulation ing surface temperature and properties Typing 65 of clothing (I ) for some typical cloth- of clothing (or skin) and surrounding Filing, seated 70 cl Filing, standing 80 ing ensembles are given in Table 2, and surfaces. The radiation heat transfer be- Walking about 100 individual resistances of various gar- tween the body and surrounding surfaces Lifting/packing 120 ment (Icli) are given in Table 3 [1, 2]. is given as follows [4, 6, 8]: Miscellaneous occupational activities Table 2. I and R values of typical clothing ensembles [1]. Cooking 90-115 cl cl House cleaning 115-120 2 Seated, heavy limb movement 130 Clothing ensemble Icl, clo Rcl, m K/W Machine Work MEN Sawing (table saw) 105 Cool socks, briefs, shoes, s.s. woven shirt, cool trousers 0.42 0.065 Light (electrical industry) 115-140 Warm socks, briefs, shoes, s.s. woven shirt, cool trousers 0.42 0.065 Heavy 235 Cool socks, briefs, shoes, s.s. cool knit shirt, cool trousers 0.55 0.085 Handling 50 kg bags 235 Cool socks, briefs, undershirt, shoes, i.s. woven shirt, cool trousers 0.51 0.079 Pick and shovel work 235-280 Cool socks, briefs, undershirt, shoes, s.s. woven shirt, warm jacket, cool 0.73 0.113 trousers0 Miscellaneous leisure activities Cool socks, briefs, shoes, cool trousers 0.31 0.048 Dancing, social 140-225 Cool socks, briefs, undershirt, shoes, s.s. woven shirt, warm jacket, warm 0.77 0.119 Tenis, singles 210-270 trousers Basketball 290-440 WOMEN Cool dress, pantyhose, bra and panties, shoes 0.21 0.032 Cool s.s. sweater, cool dress, pantyhose, bra and panties, shoes 0.30 0.046 Clothing slows down the rate of con- Warm dress, pantyhose, bra and panties, shoes 0.49 0.076 duction, and the nature of the clothing Warm skirt, warm i.s. blouse, pantyhose, bra and panties, shoes 0.41 0.063 Warm i.s. sweater, warm skirt, warm i.s. blouse, pantyhose, bra and 0.64 0.099 influences the rate of conduction loss panties, shoes (Ck). The conduction heat loss is usually Warm i.s. sweater, warm slacks, warm i.s. blouse, pantyhose, bra and 0.77 0.119 insignificant. Also, the rate of change of panties, shoes Warm i.s. sweater, warm slacks, pantyhose, bra and panties, shoes 0.59 0.091 heat stored in the body is neglected in a steady-state heat transfer with its envi- ronment [22].
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