Methods and Locations for Embedding Heating Units into Base Layers for Smart Wear: Analyzing Thermal Responses to Automatic Heat Regulation

Abstract

To set the on-off mode for efficient automatic heat regulation of a smart base layer, this study determined whether the location of the temperature input sensors for automatic heat regulation and the temperature range set for on-off was adequate in a particular environment-clothing-body system. The experimental environment was set to both neutral (23.0±1.0 °C, 20±5 % RH) and cold (5±0.5 °C, 45±5 % RH, wind velocity: 0.2 m/s). With eight male subjects wearing T-shirts and outerwear over smart base layers, both their skin temperatures and the clothing microclimate temperatures were measured when the heating unit was in operation. Wearability was thus assessed, thereby allowing an examination of the relationship between the temperature values of the input sensor and those of the heating unit. In this context, we set the reference value of the fabric-covered sensor to 34 °C and sewed the operating portion of the heat-generating pad into the inner side of the back area of the base layer. When the heating unit temperature was set to 34 °C, the clothing microclimate temperature changed in response to changes in the external environmental temperature; this was detected by the temperature sensor attached to the heating unit of the smart base layer. Thus, in both environments, the back area skin temperature was maintained almost consistently within the upper limit (38.4±2.0 °C) of the skin temperature comfort zone. As a result of examining the temperature changes according to the layering structure of clothing where the heat-generating device was attached, the location where temperature sensor A was embedded to receive the input signal within the heating unit and the set point reflected the effects of the environmental temperature, body temperature, and clothing in balance, thereby demonstrating its suitability for automatic heat regulation input signals. Here, the overall thermal sensation was 1.3–2.0 points and thus somewhat warm; overall comfort was also higher than average, at 6.4–7.3 points. In sum, neither the overall thermal sensation or comfort level substantially changed when moving to low-temperature indoor environments after wearing the automatic heat-regulating smart base layer. We therefore established that the body comfort zone was adequately maintained in both given environments when the operating portion of the device was embedded into the base layer of the three-layer clothing system and while the reference value of the sensor temperature was set.