Thermal Comfort Index as a Method of Assessing the Thermal Comfort of Textile Materials

Transcription

1 Małgorzata Matusiak Textile Research Institute ul. Brzezińska 5/5, Łódź, Poland Thermal Comfort Index as a Method of Assessing the Thermal Comfort of Textile Materials Abstract Thermal comfort is an element of clothing utility comfort. It is defined as a state of satisfaction with the thermal conditions of the environment. Thermal comfort refers to the maintenance of a roer relationshi between body heat roduction and loss. Heat exchange between the human organism and its surroundings is a comlex henomenon that deends on many factors connected with the human organism, climatic conditions of the environment, and the roerties and structure of clothing. In this aer the most imortant factors influencing heat exchange between the human body and its surroundings are discussed. A Thermal Comfort Index TCI was elaborated as a comlex characteristic of fabric from the oint of view of its ability to ensure thermal comfort in given climatic conditions. The index roosed was alied to assess the textile materials chosen. Key words: thermal comfort, thermal comfort index, thermal insulation. Introduction Thermal comfort is defined as a state of satisfaction with the thermal conditions of the environment [ - 4]. It is also considered as a lack of negative feelings caused by the thermal effects of the environment. Assurance of thermal comfort requires the thermal stability of the human through maintenance of the thermal balance between body heat roduction and loss []: Q - Q d - Q w - Q ou - Q oj = Q = = Q R + Q () K Q metabolic rate of human body in W/m2, Q d evaorative heat loss from skin surface in W/m2, Q w heat loss by the evaoration of sweat in W/m2, Q ou latent heat loss by resiration in W/m2, Q oj convective or sensible Q resiration heat loss in W/m2, total rate of heat loss from skin in W/m 2, Q R heat loss by radiation from the outer surface of the clothing in W/m 2, Q K heat loss by convection from the outer surface of the clothing in W/m 2. three ways: resiration, release of dry heat (radiation, convection, conduction) and evaorative heat. The total heat loss at a mean temerature of 20 C and relative air humidity of 50% can be divided as follows [5]: evaoration 20%, convection 25%, radiation 45%, resiration 0%. The above division of heat loss occurs during rest and when there is a lack of ventilation. At a low temerature resiration can exceed 30 % of the total heat loss, whereas at a high ambient air temerature of C, the evaoration of sweat is the main cause of heat loss. Heat exchange between the human body and its surroundings deends on many factors, which can by divided into three grous (Figure ): the human organism, climatic conditions of the environment, clothing. Thermal insulation of clothing The rotection of the human being against the influence of negative environmental factors is one of the most imortant functions of clothing. Investigation of the thermal insulation of clothing was first initiated not by textile exerts but by secialists in hysiology dealing with the design of room air conditioning [5-9]. In the years , Gagge i co. carried out an investigation of the heat exchange between the human body and its surroundings in which they introduced a unit of clothing thermal insulation Λ cl (clo) describing the total thermal resist- The human organism is homoeothermic, which means that it has to maintain its core temerature within close limits around 37 C. During all kinds of activity, the human body roduces a certain amount of heat in the range of 80 W while sleeing to even over 000 W during intensive effort. The surlus energy can be transferred to the environment in Figure. Factors influencing heat exchange between the human body and its surroundings. Matusiak M.; Thermal Comfort Index as a Method of Assessing the Thermal Comfort of Textile Materials FIBRES & TEXTILES in Eastern Euroe 200, Vol. 8, No. 2 (79)

2 ance of the layer between the human skin and the outer surface of clothing. Clo Λ cl is given by the equation: [clo] (2) Λ cl thermal resistance of clothing in clo, R cl total thermal resistance in m2 h C/kcal. One clo corresonds to the intrinsic insulation of a business suit worn by a sedentary resting male in a normally ventilated room at 2 C, 50% RH and with air ventilation of 0. m/s. In these conditions clo of the clothing is equal to 0.55 m2 K/W [7]. For winter clothes a clo of around 8 is suitable, whereas for summer conditions it is a clo of around 0.5 [8]. The thermal resistance of clothing as a set of textile materials deends mostly on the thickness and orosity of articular layers [0-3]. Due to the fact that changes in the orosity of standard textile materials used in clothing are not large, the total thermal resistance of clothing is influenced mainly by the material thickness. Changes in the humidity of textile materials caused by variations in air humidity have an insignificant influence on the value of thermal resistance of textile materials [5]. Irresective of the thermal resistance of clothing material, a key role in heat exchange is layed by the size of air layers closed between the human body and clothing surface, as well as between the articular layers of clothing. In the case of one-layer clothing, thermal comfort deends on the clothing cut and fitting to the figure of the clothing user. This is exemlified by Figure 2, which shows a thermogram from an infrared camera. In the icture a clear difference in the clothing surface temerature at different arts of the human body can be seen. Due to the large rigidity and low drae of the material, the shirt does not stick to the body on the whole surface equally - it creates folds at different distances from the surface of the body. Thus, beside the laces where the shirt material sticks directly to the body s skin, there are laces of small distance (several millimetres) between the body s skin and the shirt. In the given conditions small closed saces air is an excellent thermal insulator, limiting heat loss significantly. The temerature along erendicular line L is in the range of 26.6 C to 3.77 C, whereas along horizontal line L 2 it is from C to 3.9 C, in site of the fact that, on the whole, the surface of the shirt analysed is made of the same fabric. The difference in temerature between the extreme oints on the surface of the shirt is higher than 5 C. In the case of very loose-fitting clothing, ventilation of air layers can occur additionally due to the so-called chimney effect. At a high air velocity the dynamic ressure can cause the enetration of air stream through the clothing. The amount of air transmitted deends on the kind of material from which the clothing is made. Heat loss due to ventilation can influence the thermal insulation of clothing. The thermal insulation of multilayer clothing deends not only on the thermal insulation of articular layers but also on their number and arrangement [3, 4], as well as on the number and dimensions of air gas. Taking into consideration the comlexity of the henomenon of heat exchange between the human body and the environment, as well as the big number of factors influencing the heat exchange, an unambiguous assessment of the thermal insulation of a given clothing assortment is difficult or simly imossible. Numerous investigations have been undertaken to elaborate comfort models and indexes allowing to redict or assess the thermal comfort assured by clothing. Nevertheless, recise and reliable rediction of the thermal comfort seems to be ossible at recisely described conditions of a microclimate for a set of clothing during a given kind of activity. Such a situation can take lace in the case of cold rotective work wear for workers acting in secific cold microclimates. When designing daily-use fabrics and clothing we do not know their future user. We also do not know the majority of factors influencing thermal comfort connected with both features of the human body and climatic conditions of the environment in which the clothing will be used. However, in equal (standardised) conditions we can measure the thermal roerties of articular fabrics woven or knitted. Next, from the measurement results we can draw conclusions about the fabric s ability to ensure thermal comfort in redicted conditions of clothing alication. Elaboration of a function or one general index characterising, in a comlex way, clothing from the oint of view of its ability to ensure thermal comfort has been the object of investigation for many researchers. Fanger [] elaborated the Thermal Comfort Equation as a function of 6 arameters: f(m, I cl, v, t r, t a, P w ) (3) VarioCAM AA04282.IR8 Figure 2. Thermogram illustrating temerature distribution according to the different fittings of articular arts of shirt. 46 M metabolic rate, met ( met 58.2 W/m2), I cl cloth index in clo, v air velocity in m/s, t r mean radiant temerature in C, t a ambient air temerature in C, P w vaour ressure of water in ambient air in Pa. FIBRES & TEXTILES in Eastern Euroe 200, Vol. 8, No. 2 (79)

3 According to Hes [5], the erformance of rotective garments can be described by two or three rincial arameters sufficiently characterising the clothing s rotection and wear comfort. Hes roosed an Index of Quality IQ to characterise the comlex comfort level of a winter jacket in the following form: IQ = (R - R min ) (P - P min ) (4) R thermal resistance in m2 KW -, R min minimal value of the thermal resistance accetable from the oint of view of thermal comfort in m2 KW-, P water-vaour ermeability in %, P min minimal value of the water-vaour ermeability accetable from the oint of view of thermal comfort in m2 KW-. Militky and Matusiak [8] elaborated a rocedure for the evaluation of a Physiological Index of Comfort IC. The rocedure starts with a secification of K roerties R,..., R K characterising comfort (e.g. thermal resistance, water-vaour resistance, areal weight etc). Based on direct or indirect measurements, it is ossible to obtain some comfort characteristics x,..., x K (mean value, variance, quantiles etc.) reresenting comfort roerties. Functional transformation of these characteristics (often based on sycho-hysical laws) leads to artial comfort functions: u i = f(x i, L, H) (5) where L is the unaccetable value of a characteristic (smallest u i ) and H is the value of a characteristic for a fully accetable roduct (u i equal to the highest value - ). The hysiological Index of Comfort, IC, is the weighted average of u i with weights b i : IC = ave(u i, b i ) (6) At the Hohenstein Institutes [6] the Thermohysiological Wear Comfort vote WC T was elaborated as a combination of the quantities characterising the thermohysiological quality of a textile, according to the following formula: WC T = a R ct + a 2 F d + + a 3 K f + a 4 DG + b R ct thermal resistance F d moisture regulation index K f sweat buffering F sweat transort ΔG water retention α, α 2, α 3, α 4, α 5, β constant values. (7) FIBRES & TEXTILES in Eastern Euroe 200, Vol. 8, No. 2 (79) The WC T value can lie between very good and 6 unsatisfactory. According to Umbach [6], in order to describe the total wear comfort, the thermohysiological wear comfort vote WC T should be given together with the sensorial comfort vote WC S, which corresonds to the sensitivity of skin to mechanical irritations. An interesting and comlex solution was elaborated by Hes [5], who develoed the Comfort Evaluation System (CES), consisting of a square matrix of relative comfort arameters, as follows: R Re bw B G Fw F Cw b R thermal resistance Re water-vaour resistance bw moisture absortivity B bending rigidity G shearing rigidity Fw wet friction coefficient F dry friction coefficient Cw comression work b dry thermal absortivity The arameters in the uer row reresent the thermal comfort, values in middle row - sensorial comfort, and arameters in the bottom row - fabric handle. Matusiak alied the rank method for the evaluation of woven fabrics with resect to thermal comfort [7]. The rank rocedure is simle, but it does not take into consideration the imortance of the articular arameters used for assessment. Moreover, the rank method does not take into consideration the boundary values of all comfort-related arameters, which are the basis of fabric evaluation. Using the rank method, it is ossible to comare fabrics and to rank them from the best to the worst in terms of thermal comfort in the climatic conditions of clothing utility redicted. Thermal Comfort Index In this study, the theoretical consideration and investigation of textile materials in the asect of their thermal roerties allowed to elaborate a comlex index characterising the ability of textile materials to ensure thermal comfort. The Thermal Comfort Index (TCI) has the following form: n m x i x z i min j TCI = a + xi azj i= xi j= z j max (8) TCI Thermal Comfort Index, x i value of the ith roerty, whose increment causes an imrovement in thermal comfort; i =, 2,, n, x i min minimum value of roerty x i accetable from the oint of view of thermal comfort, z j value of the j th roerty, whose reduction causes an imrovement in thermal comfort; j =, 2,, m, z j max maximum value of the roerty z j accetable from the oint of view of thermal comfort, a = i xi n m i= i + j= j = j zj n m i= i degree of imortance of the ith roerty ( 5), j degree of imortance of the jth roerty ( 5). a i + j= The equation is valid when each value of x i x i min and each value of z j z j max. Otherwise when at least one roerty does not take the value necessary for thermal comfort assurance, a lack of comfort occurs. In this case there is little oint in calculating the comfort index. Elements: (x i - x i min )/x i and ( - z j /z j max ) take values of 0 to, which allows to revent the neglecting of imortant comfort roerties desite their small absolute value. TCI values are also in the range of 0 to. The original name of the index elaborated was the Physiological Comfort Index PCI [8]. Physiological comfort is a very comlex henomenon that covers not only the thermal but also the sensorial feeling resulting from fabric handle or its ability to accumulate electric charge. Due to this fact, the name Thermal Comfort Index seems to be more adequate than Physiological Comfort Index. The index elaborated, TCI, characterises fabrics mainly with resect to the thermal feeling of the clothing user. The index elaborated, TCI, can be alied to assess different textile materials in terms of the thermal comfort redicted. In order to calculate the value of TCI according to the formula resented (8), it is first necessary to establish the kind and number of arameters as criteria for the j 47

4 Table. The set of materials investigated. assessment. This should be done on the basis of the knowledge and exerience of the investigator or designer. Next the arameters chosen have to be divided into two grous: ositive roerties - x and negative roerties - z. Moreover, the aroriate degree of imortance can be established for each roerty used for calculation. At this stage of the investigation we do not have the necessary data to assume the accetable minimum or maximum values of the articular arameters alied for the calculation of the TCI. This roblem should be the subject of further research. The main barrier is a lack of information about the conditions of clothing usage redicted as well as the dynamic changeability of these conditions resulting from the way of clothing usage, the climatic conditions of the environment as well as the individual features and kind of clothing user activity. In the comarable analysis of textile materials by means of TCI, the minimum or maximum values of articular arameters from all their values obtained as a result of fabric measurement can be taken as x i min and z j max. 48 Symbol Descrition Material Mass er square meter, gm -2 Thickness, mm C lain woven fabric; war 5 tex, 30 cm - ; weft 20 tex, 25 cm - cotton C 2 lain woven fabric; war 5 tex, 30 cm - ; weft 40 tex, 24 cm - cotton C 3 lain woven fabric; war 5 tex, 30 cm - ; weft 60 tex, 6 cm - cotton P nonwoven stitched (Figure 3.a) cotton P 2 fluffy nonwoven PES P 3 3-layer material: lining+ nonwoven + net (Figure 3.b) PES P 4 fluffy nonwoven (Figure 3.d) PES P 5 2-layer material: lining + nonwoven (Figure 3.c) PES P 6 fluffy nonwoven PES Table 2. Results of measurement. Symbol λ, b, R, h, Ret, AP, Wm - K- 0 3 W m-2 s/2 K- W-K m2 0-3 mm m2paw- dm3m-2 s- C C C P P P P P P Exerimental The Thermal Comfort Index elaborated was alied to assess the selected textile materials on the basis of the results of instrumental measurement. The textile materials chosen differed significantly with resect to their thermal roerties, being the objects of evaluation. There were fabrics characterised by significantly different structures: cotton woven fabrics made using the same war: 5 tex, nominal density 30 cm-; PES nonwoven of various thickness, and multilayer thermoinsulating fabrics. The materials investigated are resented in Table. Measurement was done by means of an Alambeta and sweating guarded hotlate test. The following roerties were measured: λ thermal conductivity, b thermal absortivity, R thermal resistance, h fabric thickness, R et water-vaour resistance. Moreover, the air ermeability (AP) was assessed according to the standardised method PN-EN ISO 9237:998. The results obtained are resented in Table 2. On the basis of the results, the TCI values were calculated according to the formula elaborated (8) assuming the alication of the fabrics investigated to winter clothing. For the calculation of TCI, the following roerties were taken: thermal resistance water-vaour resistance thermal absortivity air ermeability with the degree of imortance given in Table 3. The thermal resistance R was taken as a ositive arameter - x, because its increase causes an imrovement in thermal comfort. Thermal absortivity b, watervaour resistance R et and air ermeability AP were taken as the negative arameters - z, because their increase causes a worsening of thermal comfort. The lower the water-vaour resistance, the better the sweat release and, in the same way, the more comfortable the feeling is. The lower the air ermeability, the better the rotection against wind, which imroves the thermal comfort, esecially in winter conditions. Furthermore, the lower thermal absortivity of fabrics means that they are warmer to the touch. The roerties mentioned above are considered as the most imortant for thermal comfort in a cold climate. It was also ossible to aly other thermal roerties of fabrics, for instance their mass er square meter or thickness. Both are imortant from the oint of view of thermal comfort. The bigger the mass and thickness, the better the thermal insulation of fabrics. Nevertheless, a bigger mass and thickness can lead to a worsening of utility comfort, esecially the freedom of movement. The degrees of imortance of articular thermal roerties alied to TCI calculation were established on the basis of the author s knowledge and exerience as an investigator and clothing user. Table 3. Degree of imortance of the roerties used for TCI calculation. No. Proerty P a. Thermal resistance Thermal absortivity Water-vaour resistance Air ermeability i 6 FIBRES & TEXTILES in Eastern Euroe 200, Vol. 8, No. 2 (79)

5 On the basis of the formula elaborated (8), values of TCI were calculated for all materials assessed. The results obtained are resented in Figure 4. For comarison, values of TCI were also calculated on the basis of 5 arameters: the 4 mentioned above (Table 3) and the mass er square meter of the fabric TCI 2. The mass er square meter was considered as a negative arameter, with a degree of imortance equal to. The results resented confirmed the substantial differences in the textile materials assessed with resect to their ability to ensure thermal comfort in winter conditions. The highest value of TCI occurred for materials P 5 and P 6. The results of the assessment are consistent with exectations. Materials P 5 and P 6 are textile materials designed esecially for the insulating layer of winter clothing. Material P 6 is a thick PES nonwoven, whereas material P 5 is a 2-layer material consisting of PES nonwoven and lining (Figure 3). According to the TCI values, both materials are comarable with resect to thermal comfort, although their articular thermal roerties are comletely different. The nonwoven P 6 is characterised by the highest thermal resistance of all the materials investigated but also by the highest water-vaour resistance. In comarison to nonwoven P 6, the 2-layer material P 5 is characterised by a lower thermal resistance but also by a much lower water-vaour resistance and air ermeability. Due to the comarable values of TCI of materials P 5 and P 6, the clothing designer has to weigh u which basic roerty is the most imortant with resect to the clothing designed and make aroriate corrections of the imortance degrees. Next the values of TCI should be calculated once again. The lowest value of TCI was noted for material C, which is thin cotton woven fabric and not really aroriate for winter clothing. Therefore the evaluation of fabric C using the TCI index TCI index seems to be correct. Values of TCI calculated on the basis of 4 fabric roerties: thermal resistance, water-vaour resistance, thermal absortivity and air ermeability (series TCI in Figure 4) are at the same level as values of TCI calculated on the basis of 5 arameters (series TCI 2 in Figure 4). Alication of the mass er square meter FIBRES & TEXTILES in Eastern Euroe 200, Vol. 8, No. 2 (79) a) b) c) d) Figure 3. Pictures of chosen investigated textile materials; a) nonwoven stitched, b) 3-layer material, c) 2-layer material, d) fluffy nonwoven. Figure 4. Calculated values of TCI : TCI values calculated without the mass er square meter of fabric, TCI 2 values calculated with mass er square meter of fabric. to the calculation of TCI did not influence the results of fabric assessment in the range of their ability to ensure thermal comfort. n Conclusions On the basis of the investigation resented, it can be stated that the Thermal Comfort Index TCI elaborated enables the assessment of fabrics with resect to their ability to ensure total thermal comfort on the basis of articular measureable thermal roerties of fabrics. Due to the lack of scientific basis to establish minimum and maximum values of articular thermal roerties necessary for thermal comfort, in order to calculate the values of TCI, the minimum or maximum values of articular arameters from all the values of these arameters obtained for the grou of fabrics investigated can be taken as xi min and zj max. The choice of roerties for calculation of the TCI should take into consideration the redicted alication of clothing made of the fabrics evaluated. The degree of imortance of articular comfort roerties of fabrics should be established on the basis of the exerience and knowledge of the textile designer. Nevertheless, it is necessary to carry out investigations in order to determine extreme values of the thermal roerties of fabrics accetable to assure thermal comfort. The investigation aimed at the elaboration of a Thermal Comfort Index as a comlex characteristic of textile materi- 49

6 als in the asect of the thermal comfort of clothing made of these materials will be continued. The 9 th International Symosium EL-TEX 200 Electrostatic and Electromagnetic Fields New Materials and Technologies will be held on May 200 in Łódź (Rąbień), Poland The Symosium is organised by: the Textile Research Institute (IW) in Łódź, the Institute of Telecommunication, Teleinformatics and Acoustics (ITT&A) of the Technical University of Wrocław, and the Polish Committee of Electrostatics (SEP), Warsaw. El-Tex Symosium has been organised by the Textile Research Institute since 994. Scientific Committee - Chairman - Prof. Tadeusz Więckowski Ph.D., D.Sc. (PWr) Organizing Committee - Chairman - Jolanta Mamenas M.Sc., Eng. (Director of IW) The main aim of El-Tex 200 is the survey and romotion of scientific, technological and alicational develoments and the exchange of exeriences between exerts reresenting different scientific discilines. The rogram will cover a selection of issues in the scoe of: the effects of electromagnetic fields (EMF) onto human health, eliminating or restricting the hazards caused by the occurrence of static electricity, environmental asects of EMF, roduction methods and alication of textile shielding materials, electrostatic evaluation of textile fabrics, the metrology of electrostatic and electromagnetic fields. Deadlines: aer/oster accetance manuscrits ready for rinting ayment of registration fee Registration fee: ayment till after EURO, 250 EURO The fee covers: articiation in sessions, CD with abstracts and resentations, boarding, and social event. Hotel costs are not included. Recommended accommodation and Symosium venue: Hotel BORYNA, address: ul. Wycieczkowa 2/0, Rąbień AB/ Aleksandrów Łódzki, Poland Booking via El-Tex200 Organizing Committee. Payments on the sot (at hotel) Information: Textile Research Institute (IW), Brzezińska 5/5, Łódź, Poland, fax: Contact ersons: Katarzyna Grzywacz tel. (+4842) , grzywacz@iw.lodz.l Joanna Korowska tel (+4842) 663 6, korowska@iw.lodz.l Acknowledgment The investigations resented in this aer were carried out within the framework of Project Nr N N funded by the Polish Ministry of Science and Higher Education in the years References. Fanger P. O.; Thermal Comfort, Arkady (974). 2. Sirvydas P. A., Nadzeikienė J., Milašius R., Eičinas J., Kerauskas P., Fibres &Textiles in Eastern Euroe, Vol. 4 No. 2 (56) (2006) Matusiak M.; Fibres &Textiles in Eastern Euroe, Vol. 4 No. 5(59) (2006) Matusiak M., Innowacyjne włókna i materiały włókiennicze orawiające komfort fizjologiczny, Przegląd Włókienniczy 2/2008, ISSN , 2008, Textiles for Protection, Woodhead Publishing in Textiles (2005). 6. Matusiak M., Modelling the Thermo Physiological Comfort of Aarel Textiles, Autex 2007 Conference, Tamere Finland (2007). 7. htt:// 8. Militky J., Matusiak M., Comlex Characterization of Cotton Fabric Thermo- Physiological Comfort, 3rd International Textile, Clothing & Design Conference, Dubrovnik (2006). 9. Hedge A., Thermal Comfort, Thermal Comfort Variables, Cornell University, (2006). 0. Żurek W., Koias K.; Structure of Textile Materials, WNT, Warsaw (977).. Gunesoglu S., Meric B., Gunesoglu C.; Fibres & Textiles in Eastern Euroe Vol. 3 No.2 (50) (2005) Ogulata R. T.; Fibres & Textiles in Eastern Euroe Vol. 5 No.2 (6) (2007) Özçelik G., Çay A., Kirtay E.; Fibres & Textiles in Eastern Euroe Vol. 5 No. (60) (2007) Sikorski K., Innowacje w odzieży zawodowej, Przegląd Włókienniczy - WOS 2/2008, ISSN , 2008, Hes L.; Alternative Methods of Determination of Water Vaour Resistance of Fabrics by Means of a Skin Model, 3rd Euroean Conference on Protective Clothing and NOKOBETEF 8, Gdynia (2006). 6. Umbach K. H.; Product Labeling Wear Comfort at the Point of Sale, Melliand Textilberichte 85 (2004) 0, Matusiak M.; Analiza wybranych właściwości fizycznych wływających na fizjologiczny komfort użytkowania lekkich tkanin bawełnianych, Przegląd Włókienniczy 2/2006. Received Reviewed FIBRES & TEXTILES in Eastern Euroe 200, Vol. 8, No. 2 (79)