Body cooling methods for improving endurance in hot environments at minimal energy.

Abstract

Personal cooling vests that incorporate phase change material (PCM) have been used to improve thermal sensation of people working outdoors in different fields (firefighting, construction, military, police, etc.). It is proposed in this study to investigate by modeling and experimentation the effect of applying different strategies to enhance the cooling effect of PCM vests and comfort of workers through: 1) targeting torso sensitive areas that trigger comfort; 2) using two PCM melting temperatures in one cooling vest and the possibility of reducing vest weight and 3) applying a two-bout strategy while reducing energy use, carried weight and material cost. A fabric-PCM model is developed and integrated with a bio-heat model to predict human thermal responses and comfort levels. Experiments on human subjects are done to validate the predictions of the integrated model and perform simulations to improve the PCM vest performance and apply the different proposed strategies. Since the PCM cooling vests have some disadvantages that involve the risk of condensation at their low temperature surface and the hindrance of moisture transport from the microclimate air near the skin to the environment, a PCM-Desiccant packet is proposed for use in cooling vests. A fabric-PCM-Desiccant model is developed and validated with experiments on a wet clothed heated cylinder. The different vest models are integrated with a bio-heat model to assess at which ambient conditions and human activity the different systems would provide enhanced cooling.