Clothing Evaporative Resistance Research Articles

Comparison of correction factor for both dynamic total thermal insulation and evaporative resistance between ISO 7933 and ISO 9920

BackgroundThermal insulation and evaporative resistance of clothing are the physical parameters to quantify heat transfer and evaporative dissipation from the human body to the environment, respectively. Wind and body movement decrease thermal insulation and evaporative resistance of clothing, which is represented as correction factors for dynamic total thermal insulation (CFi) and evaporative resistance (CFe), respectively. Then, CFi and CFe are parts of the key parameters to predict heat strain of workers by computer simulation. The objective of this study was to elucidate the difference of CFi and CFe between ISO 7933 and ISO 9920 and compare the difference of predicted rectal temperature, water loss, and exposure time limit calculated by using each correction factor.MethodsCFi of ISO 7933 (CFi7933) and ISO 9920 (CFi9920), and CFe of ISO 7933 (CFe7933) and two kinds of CFe of ISO 9920 (CFe9920a, CFe9920b) were compared in terms of relative air velocity, walking speed for three kinds of thermal insulation of clothing. Next, two modified predicted heat strain (PHS) models were developed: modified PHS integrated with CFi9920 and CFe9920a (PHSmA) and modified PHS integrated with CFi9920 and CFe9920b (PHSmB). We calculated the rectal temperature, water loss, and exposure time limit by PHS, PHSmA, and PHSmB and compared the results.ResultsCFi7933 and CFi9920 were almost similar in terms of Var and walking speed, while CFe9920a and CFe9920b were larger than CFe7933 when Var was more than 1.0 m·s−1. Intrinsic clothing insulation (Icl) diminished the effects of Var on CFi7933, CFi9920, CFe7933, and CFe9920b. However, CFe9920a was not influenced by Icl. The predicted rectal temperature and water loss difference were larger between PHS and PHSmA as CFe difference got larger. The duration time when limit of rectal temperature of 38 °C was reached (DlimTre38) calculated by PHS was significantly longer than PHSmA, PHSmB at higher Var.ConclusionsPrecise correction factors for evaporative resistance are required to predict rectal temperature, water loss, and work-time limits.

Measurement of local evaporative resistance of a typical clothing ensemble using a sweating thermal manikin

AbstractTo accurately simulate human physiology and thermal comfort, certain human physiological and comfort models categorize the human body into multiple parts. Most of these body parts are normally clothed, which must be quantified in the simulation. However, existing databases of clothing evaporative resistance only characterize the evaporative resistance of the whole body and not those of individual body parts. This implies that each body part has the same level of clothing evaporative resistance. In this research, we measure the local clothing insulation and evaporative resistance. Here, we present the local thermal characteristic values as well as the values for the whole body.

Effects of fabric thickness and material on apparent ‘wet’ conductive thermal resistance of knitted fabric ‘skin’ on sweating manikins

Currently, no published standard and research work have addressed the basic requirements on knitted fabric ‘skin’ on sweating manikins. In this study, we performed 252 experiments to investigate the influence of fabric thickness and material on the apparent ‘wet’ conductive (or effective) thermal resistance of the fabric ‘skin’ using a ‘Newton’ manikin. Four types of cotton fabric ‘skin’ (fabric thickness: 0.38, 0.54, 0.92 and 1.43mm) and three types of polyester fabric ‘skin’ (fabric thickness: 0.41, 0.54 and 1.0mm) were selected and their ‘wet’ conductive thermal resistance was determined. Empirical equations were also developed for each fabric ‘skin’ to predict wet fabric ‘skin’ surface temperatures. It was found that both fabric thickness and material significantly affected the apparent ‘wet’ conductive thermal resistance. Clothing total evaporative resistance determined using thin fabric ‘skin’ (e.g., CO1, CO2) was normally lower than that determined using thick fabric ‘skin’ (e.g., CO4). Besides, synthetic fabric ‘skin’ tended to have a larger apparent ‘wet’ conductive thermal resistance than the cotton fabric ‘skin’ due to a smaller amount of moisture contained. Hence, there is a great need to standardize the fabric ‘skin’ to eliminate the influence of fabric ‘skin’ on the measurement of clothing evaporative resistance by means of a sweating manikin.

Measurements of clothing evaporative resistance using a sweating thermal manikin: an overview.

Evaporative resistance has been widely used to describe the evaporative heat transfer property of clothing. It is also a critical variable in heat stress models for predicting human physiological responses in various environmental conditions. At present, sweating thermal manikins provide a fast and cost-effective way to determine clothing evaporative resistance. Unfortunately, the measurement repeatability and reproducibility of evaporative resistance are rather low due to the complicated moisture transfer processes through clothing. This review article presents a systematical overview on major influential factors affecting the measurement precision of clothing evaporative resistance measurements. It also illustrates the state-of-the-art knowledge on the development of test protocol to measure clothing evaporative resistance by means of a sweating manikin. Some feasible and robust test procedures for measurement of clothing evaporative resistance using a sweating manikin are described. Recommendations on how to improve the measurement accuracy of clothing evaporative resistance are addressed and expected future trends on development of advanced sweating thermal manikins are finally presented.

Effect of two sweating simulation methods on clothing evaporative resistance in a so-called isothermal condition.

The effect of sweating simulation methods on clothing evaporative resistance was investigated in a so-called isothermal condition (T manikin = T a = T r ). Two sweating simulation methods, namely, the pre-wetted fabric "skin" (PW) and the water supplied sweating (WS), were applied to determine clothing evaporative resistance on a "Newton" thermal manikin. Results indicated that the clothing evaporative resistance determined by the WS method was significantly lower than that measured by the PW method. In addition, the evaporative resistances measured by the two methods were correlated and exhibited a linear relationship. Validation experiments demonstrated that the empirical regression equation showed highly acceptable estimations. The study contributes to improving the accuracy of measurements of clothing evaporative resistance by means of a sweating manikin.

A Study on Material of Manikin Skin for Measuring Clothing Evaporative Resistance

A Study on Material of Manikin Skin for Measuring Clothing Evaporative Resistance

Thermal Effects of Design and Materials on QuadGard™ Body Armor Systems

QuadGard™ arm and leg protection systems were developed to better protect key areas of arms and legs from blast fragments. The purpose of this investigation was to use sweating thermal manikin Walter™ and examine the intrinsic clothing insulation (Rcl), intrinsic clothing evaporative resistance (Recl), micro-climate temperature, and moisture retention of three QuadGard™ systems (QG II, QG IV Ventilated, and QG IV Not Ventilated) constructed with two ballistic materials, Dyneema® and Kevlar®. With similar protection level, the ballistic material Dyneema®, consistently measured lower in Rcl and Recl than the ballistic material Kevlar®, indicating body armor made with ballistic material Dyneema® is more comfortable. There was no significant difference between QG II and QG IV Ventilated in Rcl and there was no significant difference between the three armor systems in Recl. This indicated that design features have the potential to reduce thermal stress on the human body when protective clothing is necessary.

Comments on “Correction of the evaporative resistance of clothing by the temperature of skin fabric on a sweating and walking thermal manikin”

Comments on “Correction of the evaporative resistance of clothing by the temperature of skin fabric on a sweating and walking thermal manikin”

Localised boundary air layer and clothing evaporative resistances for individual body segments

Evaporative resistance is an important parameter to characterise clothing thermal comfort. However, previous work has focused mainly on either total static or dynamic evaporative resistance. There is a lack of investigation of localised clothing evaporative resistance. The objective of this study was to study localised evaporative resistance using sweating thermal manikins. The individual and interaction effects of air and body movements on localised resultant evaporative resistance were examined in a strict protocol. The boundary air layer's localised evaporative resistance was investigated on nude sweating manikins at three different air velocity levels (0.18, 0.48 and 0.78 m/s) and three different walking speeds (0, 0.96 and 1.17 m/s). Similarly, localised clothing evaporative resistance was measured on sweating manikins at three different air velocities (0.13, 0.48 and 0.70 m/s) and three walking speeds (0, 0.96 and 1.17 m/s). Results showed that the wind speed has distinct effects on local body segments. In contrast, walking speed brought much more effect on the limbs, such as thigh and forearm, than on body torso, such as back and waist. In addition, the combined effect of body and air movement on localised evaporative resistance demonstrated that the walking effect has more influence on the extremities than on the torso. Therefore, localised evaporative resistance values should be provided when reporting test results in order to clearly describe clothing local moisture transfer characteristics. Practitioner Summary: Localised boundary air layer and clothing evaporative resistances are essential data for clothing design and assessment of thermal comfort. A comprehensive understanding of the effects of air and body movement on localised evaporative resistance is also necessary by both textile and apparel researchers and industry.

Erratum to: Effect of temperature difference between manikin and wet fabric skin surfaces on clothing evaporative resistance: how much error is there?

Erratum to: Effect of temperature difference between manikin and wet fabric skin surfaces on clothing evaporative resistance: how much error is there?

Determination of Clothing Evaporative Resistance on a Sweating Thermal Manikin in an Isothermal Condition: Heat Loss Method or Mass Loss Method?

This paper addresses selection between two calculation options, i.e heat loss option and mass loss option, for thermal manikin measurements on clothing evaporative resistance conducted in an isothermal condition (T(manikin) = T(a) = T(r)). Five vocational clothing ensembles with a thermal insulation range of 1.05-2.58 clo were selected and measured on a sweating thermal manikin 'Tore'. The reasons why the isothermal heat loss method generates a higher evaporative resistance than that of the mass loss method were thoroughly investigated. In addition, an indirect approach was applied to determine the amount of evaporative heat energy taken from the environment. It was found that clothing evaporative resistance values by the heat loss option were 11.2-37.1% greater than those based on the mass loss option. The percentage of evaporative heat loss taken from the environment (H(e,env)) for all test scenarios ranged from 10.9 to 23.8%. The real evaporative cooling efficiency ranged from 0.762 to 0.891, respectively. Furthermore, it is evident that the evaporative heat loss difference introduced by those two options was equal to the heat energy taken from the environment. In order to eliminate the combined effects of dry heat transfer, condensation, and heat pipe on clothing evaporative resistance, it is suggested that manikin measurements on the determination of clothing evaporative resistance should be performed in an isothermal condition. Moreover, the mass loss method should be applied to calculate clothing evaporative resistance. The isothermal heat loss method would appear to overestimate heat stress and thus should be corrected before use.

Effect of posture positions on the evaporative resistance and thermal insulation of clothing

Evaporative resistance and thermal insulation of clothing are important parameters in the design and engineering of thermal environments and functional clothing. Past work on the measurement of evaporative resistance of clothing was, however, limited to the standing posture with or without body motion. Information on the evaporative resistance of clothing when the wearer is in a sedentary or supine posture and how it is related to that when the wearer is in a standing posture is lacking. This paper presents original data on the effect of postures on the evaporative resistance of clothing, thermal insulation and permeability index, based on the measurements under three postures, viz. standing, sedentary and supine, using the sweating fabric manikin-Walter. Regression models are also established to relate the evaporative resistance and thermal insulation of clothing under sedentary and supine postures to those under the standing posture. The study further shows that the apparent evaporated resistances of standing and sedentary postures measured in the non-isothermal condition are much lower than those in the isothermal condition. The apparent evaporative resistances measured using the mass loss method are generally lower than those measured using the heat loss method due to moisture absorption or condensation within clothing. Statement of Relevance: The thermal insulation and evaporative resistance values of clothing ensembles under different postures are essential data for the ergonomics design of thermal environments (e.g. indoors or a vehicle's interior environment) and functional clothing. They are also necessary for the prediction of thermal comfort or duration of exposure in different environmental conditions.

Effect of temperature difference between manikin and wet fabric skin surfaces on clothing evaporative resistance: how much error is there?

Clothing evaporative resistance is one of the inherent factors that impede heat exchange by sweating evaporation. It is widely used as a basic input in physiological heat strain models. Previous studies showed a large variability in clothing evaporative resistance both at intra-laboratory and inter-laboratory testing. The errors in evaporative resistance may cause severe problems in the determination of heat stress level of the wearers. In this paper, the effect of temperature difference between the manikin nude surface and wet textile skin surface on clothing evaporative resistance was investigated by both theoretical analysis and thermal manikin measurements. It was found that the temperature difference between the skin surface and the manikin nude surface could lead to an error of up to 35.9% in evaporative resistance of the boundary air layer. Similarly, this temperature difference could also introduce an error of up to 23.7% in the real clothing total evaporative resistance (R ( et_real ) < 0.1287 kPa m(2)/W). Finally, it is evident that one major error in the calculation of evaporative resistance comes from the use of the manikin surface temperature instead of the wet textile fabric skin temperature.

Development and Validation of an Empirical Equation to Predict Wet Fabric Skin Surface Temperature of Thermal Manikins

Thermal manikins are useful tools to study clothing comfort and environmental ergonomics. The simulation of sweating can be achieved by putting a highly wicking stretchable knit fabric “skin” on top of the manikin. However, the addition of such a fabric skin makes it difficult to accurately measure the skin surface temperature. Moreover, it takes considerable amount of time to measure the fabric skin surface temperature at each test. At present the attachment of temperature sensors to the wet fabric skin is still a challenge. The distance of the sensors to the fabric skin could significantly influence the temperature and relative humidity values of the wet skin surface. Hence, we conducted an intensive skin study on a dry thermal manikin to investigate the relationships among the nude manikin surface temperature, heat losses and the fabric skin surface temperature. An empirical equation was developed and validated on the thermal manikin „Tore‟ at Lund University. The empirical equation at an ambient temperature 34.0 oC is Tsk =34.00-0.0103HL. This equation can be used to enhance the prediction accuracy of wet fabric skin surface temperature and the calculation of clothing evaporative resistance.

Development and validity of a universal empirical equation to predict skin surface temperature on thermal manikins

Clothing evaporative resistance is an important input in thermal comfort models. Thermal manikin tests give the most accurate and reliable evaporative resistance values for clothing. The calculation methods of clothing evaporative resistance require the sweating skin surface temperature (i.e., options 1 and 2). However, prevailing calculation methods of clothing evaporative resistance (i.e., options 3 and 4) are based on the controlled nude manikin surface temperature due to the sensory measurement difficulty. In order to overcome the difficulty of attaching temperature sensors to the wet skin surface and to enhance the calculation accuracy on evaporative resistance, we conducted an intensive skin study on a thermal manikin ‘Tore’. The relationship among the nude manikin surface temperature, the total heat loss and the wet skin surface temperature in three ambient conditions was investigated. A universal empirical equation to predict the wet skin surface temperature of a sweating thermal manikin was developed and validated on the manikin dressed in six different clothing ensembles. The skin surface temperature prediction equation in an ambient temperature range between 25.0 and 34.0 °C is T sk =34.0–0.0132HL. It is demonstrated that the universal empirical equation is a good alternative to predicting the wet skin surface temperature and facilitates calculating the evaporative resistance of permeable clothing ensembles. Further studies on the validation of the empirical equation on different thermal manikins are needed however.

A Study on Evaporative Resistances of Two Skins Designed for Thermal Manikin Tore under Different Environmental Conditions

A cotton skin and Gore-Tex skin were designed for thermal manikin Tore to simulate different sweating styles (wet cotton skin inside and Gore-Tex outside to simulate sweating style of thermal manikin Walter, and Gore-Tex skin inside with wet cotton skin outside to simulate sweating style of thermal manikins Newton. The evaporative resistances of two skin combinations with clothing ensembles were compared at two different environmental conditions. In addition, the total evaporative resistance of clothing ensemble was calculated by both heat loss method (option 1) and mass loss method (option 2) according to ASTM F 2370. We found that the effect of different sweating mechanisms on clothing evaporative resistance should be considered. The results showed that the total evaporative resistances obtained by option 2 were more accurate than values by option 1 under an isothermal condition. It was also found that total evaporative resistance differences between two skin combinations with clothing ensembles decreased with increasing clothing ensemble layer. In a non-isothermal condition, the total evaporative resistance calculated by option 1 was more accurate than value obtained by option 2, which was due to lower ambient temperature and condensation between each adjacent layer. (Less)

Assessment of Clothing Effects in Thermal Comfort Standards: A Review

AbstractThere are four international standards covering the measurement of thermal resistance of clothing, i.e., ISO 15831, ASTM F 1291, ASTM F 1720, and EN 342. They employ the same measurement technique, but they differ in manikin size, test conditions, formula for calculating the insulation, and the parameters for reporting the test results. ASTM F 2370 is the only standard that addresses the measurement of evaporative resistance of clothing. It specifies the configuration of sweating thermal manikin, test protocol and test conditions, and does not call for a specific technique to simulate body sweating. ISO 9920 provides formulas for estimating thermal insulation and evaporative resistance of clothing. The international standards for the assessment of thermal comfort or thermal strain of a clothed body include ISO 7730, ISO/TR 11079 and ISO 7933, for evaluating moderate thermal, cold and hot environments, respectively. Their applications of thermal properties of clothing, principles, and limitations vary. Several suggestions are finally projected with regard to the future revision of these standards.

New functions and applications of walter, the sweating fabric manikin.

In this paper, latest developments on Walter, a sweating fabric manikin, are reported. These include the improved simulation of "walking motion", the design and construction of an automated water supply, and real-time measurement of evaporative water loss and regulation of "skin" temperature through the regulation of the pumps inside the manikin body. Testing of commercial garment ensembles showed that the measurement of thermal insulation and moisture-vapour resistance of clothing is very reproducible with the coefficient of variation being generally less than 5%. It was also shown that, in addition to the thermal insulation and moisture-vapour resistance, the percentage of moisture accumulation within clothing is a very useful parameter of clothing comfort. The improved manikin has been used to investigate the effects of walking motion on thermal insulation and evaporative resistance of clothing. The trend of the effects of walking speed up to 1.13 m s(-1) for the nude manikin and when it was wearing garments of different sizes are reported.

The effects of wind and human movement on the heat and vapour transfer properties of clothing

This paper integrates the research presented in the papers in this special issue of Holmér et al. and Havenith et al. [Holmér, I., Nilsson, H., Havenith, G., Parsons, K. C. (1999) Clothing convective heat exchange: proposal for improved prediction in standards and models. Annals of Occupational Hygiene, in press; Havenith, G., Holmér, I., den Hartog, E. and Parsons, K. C. (1999) Clothing evaporative heat resistance: proposal for improved representation in standards and models. Annals of Occupational Hygiene, in press] to provide a practical suggestion for improving existing clothing models so that they can account for the effects of wind and human movement. The proposed method is presented and described in the form of a BASIC computer program. Analytical methods (for example ISO 7933) for the assessment of the thermal strain caused by human exposure to hot environments require a mathematical quantification of the thermal properties of clothing. These effects are usually considered in terms of 'dry' thermal insulation and vapour resistance. This simple 'model' of clothing can account for the insulation properties of clothing which reduce heat loss (or gain) between the body and the environment and, for example, the resistance to the transfer of evaporated sweat from the skin, which is important for cooling the body in a hot environment. When a clothed person is exposed to wind, however, and when the person is active, there is a potentially significant limitation in the simple model of clothing presented above. Heat and mass transfer can take place between the microclimate (within clothing and next to the skin surface) and the external environment. The method described in this paper 'corrects' static values of clothing properties to provide dynamic values that take account of wind and human movement. It therefore allows a more complete representation of the effects of clothing on the heat strain of workers.