Passive cooling garments for outdoor thermal adaptation: a field experiment

Thermal adaptation and mitigation measures have been actively undertaken owing to warming climates, focusing on human-centered designs. Because clothing affects human energy balance namely thermal comfort, a suitable choice of clothing can be thermal adaptation. Similar to typical urban mitigations, two passive cooling techniques, which are ventilation and solar reflection were applied to a conventional garment. Accordingly, four types of garments (non-reflective loose-fitting, non-reflective tight-fitting, solar-reflective loose-fitting, and solar-reflective tight-fitting) were prepared and investigated by participants in terms of physical thermal load and subjective perceptions. Field measurements during walking were conducted in summer outdoors. Overall human thermal loads for clothed participants were smaller than undressed condition, indicating wearing clothing fundamentally acts as a buffer against environments suggesting comfort. Because the main heat-gain mechanism outdoors is irradiation, significant difference was observed in radiative heat gain between reflective loose and non-reflective loose, as well as reflective tight and non-reflective tight wearers. Despite the main cooling mechanism is convective heat loss, no significant difference in convective heat loss between loose and tight fitting garments were observed. Observed relationships among thermal sensation, thermal comfort, and human thermal load further suggest the validity of the experiments. Ideally, garments with both reflective and ventilation can improve thermal exposure significantly compared with the conventional garment. Our small scheme for heat adaptation in summer outdoor was confirmed in human energy balance; however, it did not work satisfactorily in perceptions, and thus more effective measures accompanying with detailed understanding of clothing effects are expected even under varying climate conditions.