A Comparison of Three Different Calculation Methods for Clothing Evaporative Resistance

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.