A Comparison of Three Different Calculation Methods ...

Proceedings of the 5th European Conference on Protective Clothing (ECPC), Valencia, Spain

A Comparison of Three Different Calculation Methods of Clothing Evaporative Resistance Faming Wang1,2, Chuansi Gao1, Kalev Kuklane1, Ingvar Holmér1 1. Thermal Environment Laboratory, Department of Design Sciences, Lund University, Lund, Sweden 2. Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Protection and Physiology, St. Gallen, Switzerland Contact person: [email protected]

Abstract Clothing evaporative resistance is an important input for both models dealing with heat stress and heat strain issues and standards. Both ASTM F2370 (2010) and ISO 9920 (2007) give two calculation options: heat loss option and mass loss option. For data obtained on multi-segment sweating thermal manikins, there are still two possible ways to calculate evaporative resistance for each option: the parallel way and the serial way. Due to that available standards haven’t commented on how to select one from these calculation options, it is useful to compare those methods and give a suggestion on how to choose a reasonable one for different applications. Five sets of clothing ensembles were selected for the study. A pre-wetted fabric skin was dressed on a dry heated manikin to simulate sweating. The manikin sweats at 12 segments except the head, hands and feet. The fabric skin temperature at each segment was measured by a temperature sensor. All experiments were repeated at least twice to ensure a good repeatability (±5%). All test were conducted in a so called isothermal condition (Tmanikin=Ta=Tr=34.0 °C). The results showed that the clothing evaporative resistances by the heat loss option calculated in a serial way were 15 to 46% higher than those by the heat loss option calculated in a parallel method. In contrast, the evaporative resistances calculated by the heat loss option in a parallel way were 10-27 % higher than those calculated by the mass loss option. Similarly, the evaporative resistances produced by the heat loss option in a serial way were 3-26% higher than those created by the heat loss option in a parallel way. The conclusion of this study was that clothing evaporative resistances calculated by the same option in the same way are preferably comparable. The isothermal mass loss method is always a correct choice for calculating evaporative resistance when reporting the values of tested garments. In order to keep wearers safe, the heat loss method with a serial way is always a conservative selection to calculate clothing evaporative resistance as an input for heat stress and heat strain models. Finally, a new EN or ISO standard on how to perform sweating manikin measurements to determine accurate clothing evaporative resistance values is required. Keywords: evaporative resistance, calculation option, clothing ensemble, sweating manikin

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Proceedings of the 5th European Conference on Protective Clothing (ECPC), Valencia, Spain

Supplementary materials Calculation options of clothing evaporative resistance Heat loss method (parallel option) The parallel option calculates the area weighted average evaporative heat loss first

psk  pa A  Hei ( i )  A i 1

R et _ heat , p 

n

Eq.(1)

Heat loss method (serial option) The serial option calculates segmental evaporative resistance first, and then area weighted n

R et _ heat ,s   i 1

Ai psk ,i  pa ( ) A Hei

Eq.(2)

Mass loss method (parallel and serial options) Ret _ mass , p 

psk  pa  Ai dmi 1    A  ( dt  A )  i 1  i  n

  A  p  p a    i  sk ,i dmi 1 i 1  A      dt Ai n

Ret _ mass ,s

     

Eq.(3)

Eq.(4)

where, Ret_heat,p, Ret_heat,s, Ret_mass,p, and Ret_mass,s are the total clothing evaporative resistance calculated by the parallel heat loss method, serial heat loss method parallel mass loss method and serial mass loss method, respectively, kPa·m2/W; A and Ai are the total sweating surface area and segmental sweating surface area, respectively, m2; i is the number of segment of the sweating thermal manikin (i=1,2,…, n); psk and psk,i are the water vapour pressure on the whole fabric skin surface and local fabric skin surface, respectively, kPa; Hei is the segmental evaporative heat loss, W/m2;  is the heat of vaporization of water at the measured skin surface temperature, J/g; the ratio of dmi/dt is the segmental evaporation rate of moisture leaving the manikin’s sweating surface, g/h. Currently, all sweating thermal manikins simulate evenly sweating over the whole body, and thus the local sweat rate equals to the mean sweat rate. However, the segmental mass loss rate (i.e., evaporation rate, if no water dripping) varies among segments because the segmental evaporative heat transfer coefficient is different at each segment (segmental body shape is different). Hence, it seems very difficult to apply parallel or serial mass loss method (i.e., Eqs. 3 and 4) for calculations. Therefore, the below equation is widely used for calculations (based on total mass loss rate from the clothed sweating manikin): The results of three calculations (Eqs. 1, 2, and 5) are presented in Fig.1. Ret _ mass 

psk  pa dm 1   dt A

Eq. (5) 2

Proceedings of the 5th European Conference on Protective Clothing (ECPC), Valencia, Spain

Fig.1 Clothing evaporative resistances calculated by different methods. mass, the mass loss option (Eq.5); heat_p, the heat loss option calculated in a parallel way (Eq.1); heat_s, the heat loss option calculated in a serial way(Eq.2). L, light clothing; HV: high visibility clothing; MIL: military jackets and trousers; CLM: climber overall with Gore-Tex membrane; FIRE: fire fighting clothing. Table 1 Suggestions on how to perform wet tests to determine clothing evaporative resistance by means of a sweating thermal manikin Suggestions on what you should do Use fabric skin surface temperature for any calculation of clothing evaporative resistance Use the same calculation method for all calculations, isothermal mass loss method is a good choice Carry out experiments in a so-called isothermal environment (or real isothermal, if possible) to eliminate complex heat and mass transfer pathways Make sure the fabric skin is tightly attached on the manikin body surface Make sure the segmental evaporative heat loss should be greater than 20 W/m2 The moisture content of the clothing should be controlled in a certain amount range, neither dry nor dripping Control the supplied water flow temperature close to fabric skin surface temperature

Suggestions on what you should NOT do Use manikin surface temperature for calculations Use different calculation options without indicating which option is used Perform experiments in cool ambient environments where condensation may occur Use loose fabric skin and there is a large amount of air gap between fabric skin and manikin body The segmental heat loss is too low (near 0) or too high that reached the maximal heating power Continuously measure an ensemble for many times without conditioning before the next wet test Too large temperature difference between water flow and manikin surface temperature 3

Proceedings of the 5th European Conference on Protective Clothing (ECPC), Valencia, Spain

Table 2 Calculation options of clothing evaporative resistance used for current full scale sweating thermal manikins Thermal manikin Coppelius KEM Newton

Owners (or buyers) TUT, Finland, NCSU, USA KEM, Japan MTNW, Seattle, USA

Segment 18 (13) 17 20, 26, 34

SAM

EMPA, Switzerland

30

Tore Walter

Lund University, Sweden HKPU, Hong Kong

17 (12) 1

Calculation options Mass loss method Mass loss method Heat loss method (M), mass loss method (P) Heat loss method (M), mass loss method Heat loss method, mass loss method Mass loss method

Note: TUT: Tampere University of Technology; NCSU: North Carolina State University; KEM: Kyoto Electronics Manufacturing; MTNW: Measurement Technology Northwest; EMPA: the Swiss Federal Laboratories for Materials Science and Technology; HKPU: the Hong Kong Polytechnic University; M denotes that the option is mainly used; P denotes that the option may be applied for calculations. The values in the bracket show the number of segment that used for simulated sweating (some manikins do not sweat at the head, hands and feet).

References ASTM F2370 (2010) Standard test method for measuring the evaporative resistance of clothing using a sweating manikin. PA: American Society for Testing and Materials. Fukazawa T, Lee G, Matsuoka, Kano and Tochihara Y (2004) Heat and water vapour transfer of protective clothing systems in a cold environment, measured with a newly developed sweating thermal manikin. Eur J Appl Physiol 92:645-8. ISO 9920 (2009) Ergonomics of the thermal environment-Estimation of thermal insulation and water vapour resistance of a clothing ensemble. Geneva: International Organization for Standardization. Richards M and McCullough EA (2005) Revised interlaboratory study of sweating thermal manikins including results from the sweating agile thermal manikin. J ASTM Int 2:1-13. Wang F (2011) Clothing evaporative resistance: its measurements and application in prediction of heat strain. Ph.D. Thesis, Lund University, Sweden. Wang F, Gao C, Kuklane K and Holmér I (2011) Determination of clothing evaporative resistance on a sweating thermal manikin in an isothermal condition: heat loss method or mass loss method?. Ann Occup Hyg 55:775-83. Wang F, Kuklane K, Gao C and Holmér I (2009) A study on evaporative resistances of two skins designed for thermal manikin Tore under different environmental conditions. J Fiber Bioeng Inform 1:301-5. Wang F, Kuklane K, Gao C and Holmér I (2010) The development and validation of empirical equations to predict sweating skin surface temperature for thermal manikins under non-isothermal conditions. J Therm Biol 35:197-203. Wang F, Kuklane K, Gao C and Holmér I (2012) Effect of temperature difference between manikin and wet fabric skin surfaces on clothing evaporative resistance: how much error is there?. Int J Biometeorol 56:177-82. 4