[Objective] Numerical heat and moisture transfer model of clothing is a crucial tool for evaluating clothing protective performance, calculating body-environment heat and moisture transfer, and assessing human safety during cold exposure. Existing models primarily concentrate on conventional passive protective clothing (PPC). However, actively-heated clothing (AHC) remains poorly understood, with fiber research being the primary focus in previous studies, which cannot simulate dressing conditions of the human body. In this study, we developed a multilayer heat and moisture transfer model of AHC, which can be coupled with a human thermal response model.[Methods] First, based on a published model of PPC, the heat production and transfer mechanism of active heating technologies, including electrical heating, phase change material (PCM), and moisture-absorption heating, were considered. Accordingly, we developed a general model for AHC. Particularly, the heat production of electrical heating was calculated using system voltage, current, and efficiency, and that of PCM was calculated using the phase change speed ratio and enthalpy. For moisture-absorption heating, the heat production was obtained using the moisture-absorption and heat-generation curves of the fabric, calculated by applying the specific heat and temperature change ratio. Second, we specifically considered electrically-heated clothing (EHC), which is the most widely used in practical applications. Further, the model was improved for EHC considering the clothing's detailed layer structure and radiative and horizontal heat transfer. The clothing layer containing the heating pad was further divided into interlining, pad, and fabric layers to establish more realistic heat-transfer equations. The radiative heat transfer between two clothing layers was derived using the Stefan-Boltzmann law, as heat radiation is significant in EHC systems. The body segment containing the heat area was further divided into heated and nonheated zones, in which horizontal heat transfer was modeled to accurately calculate the local skin temperature.[Results] The model coupled with a published human thermal response model was validated with existing experiments with air temperatures ranging from -20℃ to 8℃. Moreover, the general model was validated with data from an EHC experiment at 8℃ and a PCM clothing experiment at 5℃. The errors of mean skin, core, and microclimate temperatures did not exceed 0.58℃, 0.16℃ and 1.59℃, respectively. The improved EHC model was validated with data from a series of experiments with air temperatures ranging from -20℃ to 0℃ and air velocities from 0 to 5 m/s. Considering the thermal response prediction, the errors of mean skin, local skin, and core temperatures did not surpass 0.20℃, 0.47℃, and 0.14℃, respectively. Moreover, considering clothing evaluation, the error of effective heating power was ~0.10 W.[Conclusions] The proposed model can be used to assess human thermal safety and clothing protective performance in cold exposure cases with AHC and serve as a reference for personal protection, emergency management, and protective equipment research in the field of public safety and environmental ergonomics. © 2023 Press of Tsinghua University. All rights reserved.
