Annals of Occupational Hygiene Advance Access originally published online on July 20, 2006
Annals of Occupational Hygiene 2006 50(8):833-842; doi:10.1093/annhyg/mel050
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Prediction of Clothing Thermal Insulation and Moisture Vapour Resistance of the Clothed Body Walking in Wind
1 Institute of Textiles and Clothing, The Hong Kong Polytechnic University Hung Hom, Kowloon, Hong Kong
2 School of Textiles, The Tianjin Polytechnic University Tianjin, China
*Author to whom correspondence should be addressed. E-mail: tcfanjt{at}inet.polyu.edu.hk
| ABSTRACT |
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Clothing thermal insulation and moisture vapour resistance are the two most important parameters in thermal environmental engineering, functional clothing design and end use of clothing ensembles. In this study, clothing thermal insulation and moisture vapour resistance of various types of clothing ensembles were measured using the walking-able sweating manikin, Walter, under various environmental conditions and walking speeds. Based on an extensive experimental investigation and an improved understanding of the effects of body activities and environmental conditions, a simple but effective direct regression model has been established, for predicting the clothing thermal insulation and moisture vapour resistance under wind and walking motion, from those when the manikin was standing in still air. The model has been validated by using experimental data reported in the previous literature. It has shown that the new models have advantages and provide very accurate prediction.
Keywords: clothing physical characteristics moisture vapour resistance prediction model thermal insulation walking-able sweating manikin
| INTRODUCTION |
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Clothing thermal insulation and moisture vapour resistance are two most important parameters in thermal environmental engineering, functional clothing design and end use of clothing ensembles. They are intrinsic properties of clothing depending on the fabric properties, garment(s) style and fitting, and are affected by body posture, body motion and environmental conditions.
The thermal insulation and moisture vapour resistance can be measured by taking measurements on human subjects. This method gives realistic results, but requires sophisticated equipment and is time consuming, and the measured values may also have large variability. Human-shaped thermal manikins which can simulate the heat and mass transfer between human body and environment have therefore been developed for the purpose. Measurements on thermal manikins are more reproducible, but the manikins are generally very expensive and very few can simulate perspiration effectively. So it is desirable to predict the clothing thermal insulation It and moisture vapour resistance Rt, not only because of the limitations of measuring these parameters on human subjects and thermal manikins, but also because of the fact that it is practically impossible to measure It and Rt for endless clothing ensembles under the different body movement and various environment conditions.
Although considerable work has been carried out so far for predicting the clothing thermal insulation and moisture vapour resistance under various conditions (Spencer-Smith, 1977a,b; Lotens and Havenith, 1991; ISO,1995; Holmer et al., 1999; Nilssion et al., 2000), the reduction of thermal insulation or moisture vapour resistance induced by wind in the existing models was considered in very different forms. Heat and mass transfer and its interaction in clothing system are very complex processes. In order to predict or achieve the optimum performance with regards to clothing thermal comfort, knowledge of the effects of body motion and environmental parameters, especially wind velocity and walking speed, is essential.
In this study, clothing thermal insulation and moisture vapour resistance of various types of clothing ensembles were measured using the walking-able sweating manikin, Walter (Fan and Qian, 2004) under various environmental conditions and walking speeds. Based on an extensive experimental investigation and an improved understanding of the effects of body activities and environmental conditions, a simple but effective direct regression model has been established for predicting the clothing thermal insulation and moisture vapour resistance under wind and walking motion from those when the manikin was standing in still air.
| EXPERIMENTAL DESIGN AND RESULTS |
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Description of clothing ensembles
In the present study 32 sets of clothing ensembles were tested. The clothing ensembles consisted of the same pair of pants, but vary in the top garments. The pants were a casual pair from Giordano, made of a fabric with a composition of 98% cotton and 2% lycra. The top garments of the clothing ensembles are described in Tables 1 and 2.
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In Table 2, Jacket 1 and Jacket 2 represent a leisure jacket and a jacket in which two layers of fabric are combined, respectively. The thickness and the air permeability apply to the shell fabric, measured using the FAST system (SiroFAST, 1989) and ASTM D737-96 method (ASTM Book of Standards, 2004). The garment fit index is defined as the area-weighted average of the percentage difference between the inner circumferences of different parts of the garment and the corresponding circumferences of body.
Experimental conditions and results
Figure 1 shows a picture of the sweating fabric manikin, Walter (Fan and Chen, 2002; Fan and Qian, 2004) used for the investigation.
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Walter has a man's body; its size and configurations are similar to a typical Chinese man. Walter simulates perspiration using a waterproof, but moisture-permeable, fabric skin, which holds the water inside the body, but allows moisture vapour to pass through the skin. Walter achieves a body temperature distribution similar to a real person by having warm water at the body temperature (37°C) pumped from its centre to its extremities. The mean skin temperature of Walter can be adjusted by regulating the pumping rate of the pumps inside the manikin. The regulation is performed by altering the frequency of the power supply to the pumps. Walter's skin can be unzipped and interchanged with different versions to simulate different rates of perspiration. Water is supplied automatically and water loss by perspiration is measured in real time. Walter's arms and legs can be motorized to simulate walking motion. The walking speed may be changed from 0 m s1 (standing) to 2.7 km h1 by adjusting AC frequency of the power supply to the motor that drives the motion. Unlike most existing manikins, Walter has thermal insulation and moisture vapour resistance measured simultaneously.
With this manikin, the total thermal insulation It and moisture vapour resistance Rt of clothing can be measured and calculated by the following equations:
![]() | (1) |
![]() | (2) |
![]() | (3) |
![]() | (4) |
All tests were conducted in the climatic chamber under the environmental temperature of 20 ± 0.3°C and humidity of 50 ± 5%. Each of the 32 sets of clothing ensembles was tested under six levels of wind velocity (Vwind = 0.22, 0.85, 1.69, 2.48, 3.12 and 4.04 m s1, with Vwind = 0.22 m s1 representing the no wind condition) when the manikin was in standing position. At the wind velocity of 0.22 and 2.48 m s1, the clothing ensembles were also tested at four levels of walking motion (Vwalk = 0, 0.23, 0.46 and 0.69 m s1 with Vwalk= 0 m s1 representing the standing position). So for each clothing ensemble, there are 12 cases investigated. With overnight operation, it took about 2 days to complete all measurements for each clothing ensemble.
Experimental results of the measurements are listed in Supplementary Table 2 in the on-line Supplementary Material to this article.
| BUILDING A NEW DIRECT REGRESSION PREDICTION MODEL |
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Effect of wind velocity
In the existing prediction models, the reduction of thermal insulation or moisture vapour resistance by wind was considered in very different forms. Spencer-Smith (1977a,b) used a linear relationship, Loten and Havenith (1991) used the square root function, whereas Holmer et al. (1999) and Nilsson et al. (2000) used a complex exponential function to model the effect of wind velocity. It is therefore necessary to investigate the best way to model the effect of wind velocity before an improved prediction model can be established. Figure 2a and b plot the clothing thermal insulation and moisture vapour resistance against the wind velocity for three clothing ensembles. It can be seen that there is a general trend that clothing thermal insulation or moisture vapour resistance decreases with the increase in wind velocity, but the rate of reduction decreases with the increase in wind velocity.
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The reduction ratios, FI and FR, for thermal insulation and for moisture vapour resistance can be expressed as:
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The reduction ratios, FI and FR, are related to the wind velocity; they are plotted against the wind velocity for three clothing ensembles in Fig. 3a and b as examples. As can been seen, the reduction ratios, FI and FR, have approximately linear relations with the wind velocity. The slopes of FI and FR versus the wind velocity may vary with different types of clothing ensembles. Figure 4a and b plot the FI and FR versus the wind for all clothing ensembles tested in the present study. As can been seen, the approximate linear relationship between FI and FR and the wind velocity holds for all clothing ensembles tested and the slopes vary within certain ranges.
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Therefore, we can assume:
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KI and KR can be obtained by linear regression for each clothing ensemble. The values are listed in Supplementary Table 4 in the on-line Supplementary Material.
Effect of walking speed
Figure 5a and b plot the clothing thermal insulation and moisture vapour resistance against walking speed for three clothing ensembles under two windy conditions. As can be seen, the clothing thermal insulation and moisture vapour resistance decrease with increasing walking speed, and the ratio of reduction decreases with increasing walking speed and wind velocity. This is similar to the effect of wind velocity on clothing thermal insulation and moisture vapour resistance.
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Therefore, we can use an equivalent wind velocity to take into account the effect of walking speed. By analogy with the definition of effective wind velocity veff for the surface thermal insulation and surface moisture vapour resistance (Lotens and Havenith, 1991; Qian and Fan, 2005), let us define:
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Using the values of KI and KR listed in Supplementary Table 3 in the on-line Supplementary Material, ßF can be obtained by fitting equations (9) and (10), using vF from equation (11) instead of the wind velocity.
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The new regression model
Substituting equations (6) and (8) with equations (9)(12) and rewritten as below:
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In Supplementary Table 4 in the on-line Supplementary Material, it can be seen that KI may vary from 0.24 to 0.31, and KR may vary from 0.23 to 0.42, depending on the clothing characteristics such as fabric air permeability, garment style, garment fitting and clothing construction. Using the average values of KI and KR, we have:
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| VALIDATION OF THE MODELS |
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The models are based on the experimental data of 32 sets of clothing ensembles, including tight and loose fit garments, jackets, shirts and uniforms with permeable and impermeable outer fabrics. These clothing assembles were tested on the walking-able sweating manikin Walter in a climate chamber under 20°C and 50% RH, with the wind velocity and walking speed varying from 0.22 to 4.04 m s1 and 0 to 0.69 m s1, respectively. The static total thermal insulation and moisture vapour resistance of the clothing ensembles ranged 1.13
1.93 clo (0.1750.299 m2 °C W1) and 30.07
51.91 m2 Pa W1, respectively. Although this has been a systematic experimental investigation, the models developed based on these limited experimental data were validated with experimental data from other sources. The database used to validate the models includes those reported in the published literatures. Some of these data were obtained from manikins (Hong, 1992; Holmer et al., 1996; Bouskill et al., 2002; Adair, 2005) and some were from measurements on human subjects (Nielsen et al., 1985; Lotens and Havenith, 1988; Havenith 1990a,b). Figure 7 plots the measured dynamic thermal insulation against the values predicted using the new direct regression model developed in the present study with all database. As can be seen, the new direct regression model predicts the measured thermal insulation from both our experiments on the sweating manikin, Walter, and those reported in the literature quite well. There is however some underestimation for clothing ensembles with high thermal insulation, particularly for the two winter ensembles tested by Holmer et al. and one winter ensemble tested by Bouskill et al. (2002). This may be due to the fact that, in the experimental data used for establishing the new direct regression model, there is no winter clothing ensemble as warm as those two tested by Holmer et al. and that tested by Bouskill et al. (2002).
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Figure 8 plots the measured clothing moisture vapour resistance against the values predicted using the new direct regression model. With the exception for the data of the impermeable rain coverall tested by Havenith et al. on human subjects using the tracer gas method, the new direct regression model provides very good prediction. The squared correlation coefficient of the new direct regression model would be 0.91, if the data of the impermeable rain coverall tested by Havenith et al. on human subjects using the trace gas method was omitted in the analysis.
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| CONCLUSIONS |
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From the experimental investigation, it was shown that clothing thermal insulation and moisture vapour resistance decrease with increasing wind velocity and walking speed. The effects of walking speed for the total thermal insulation and moisture vapour resistance of clothing system are equivalent to 180% of the wind velocity.
Based on an improved understanding of the effects of wind and walking motion on the clothing thermal insulation and moisture vapour resistance, a simple, but effective regression model was developed for predicting the dynamic clothing thermal insulation and moisture vapour resistance under walking motion and windy conditions from the values of the clothing thermal insulation and moisture vapour resistance measured under person standing in the still air. For the prediction parameters, KI and KR, it was found that different clothing ensembles have different values of KI and KR, and they are significantly affected by the air permeability of the outer fabric, fit index and garment style as well as whether or not there is underwear on the body. Generally, the average values of KI and KR can be selected to predict It and Rt.
| APPENDIX |
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Variables
ßF = an equivalent factor of walking speed for the total clothing thermal insulation and moisture vapour resistance.
= evaporative heat of water at the skin temperature,
= 0.67 W h g1 (35oC).
Ap = the air permeability [l (m2 s)1] of clothing fabrics.
As = the body (manikin) surface area in m2.
FI = the reduction ratio for the total thermal insulation of clothing ensembles [defined by equation (8)].
Fit = the garment fit index.
FR = the reduction ratio for the total moisture vapour resistance of clothing ensembles under an equivalent wind velocity related to standing in still air situation.
Ha = the energy required to heat the water supplement to manikin's body temperature in W.
Hd = the dry heat loss from the manikin in W.
He = the evaporative heat loss from skin to the environment in W.
Hp = the heat generated from the pump in W.
Hs = the heat generated from the heating elements in the manikin in W.
Ist = the total thermal insulation of garment in the case of body standing in still air (m2 °C W1).
It = the total thermal insulation (m2 oC W1) of clothing ensembles under any situation.
KI = the slopes of the curve of FI versus the wind velocity.
KR = the slopes of the curve of FR versus the wind velocity.
psa = the saturated moisture vapour pressure at environment temperature in Pa.
pss = the saturated moisture vapour pressure at the skin temperature in Pa.
Q = the water loss (or perspiration rate) from the manikin (g h1).
Res = the moisture vapour resistance of the manikin skin (8.6 Pa m2 W1).
RHa = the relative humidity of the environment in %.
Rst = the total moisture vapour resistance of garment in the case of body standing in still air (Pa m2 W1).
Rt = the total moisture vapour resistance (Pa m2 W1) of clothing ensembles under any situation (Pa m2 W1).
Ta = the environmental temperature in °C.
Ts = the area weighted mean skin temperature in °C.
v0 = the air current in the still air condition. In this study, v0 = 0.22 m s1.
vF = an equivalent wind velocity (m s1).
Vwalk = walking speed (m s1).
Vwind = wind velocity (m s1).
| ACKNOWLEDGEMENTS |
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The authors wish to thank the University Grant Council of Hong Kong SAR for funding the project through a CERG grant no. PolyU5148/01E.
Received June 2, 2005; in final form May 30, 2006
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