Thermal Harvesting Potential of the Human Body

Abstract

Thermoelectric energy harvesting of human body heat might supplement or even replace conventional energy storage in wearable devices for healthcare and the Internet of Humans. Although a number of thermal harvesters are presented in the literature, no conclusive data can be found on the amount of available thermal energy provided by different individuals and activities. We here present the results of an observational study with 56 test subjects of different ages (children, adults and elderly) and gender, performing predefined activities (sitting, walking) in varying environments (indoor, outdoor). Our study showed a statistical difference of thermal potential and skin properties between age groups, but not between genders. On average, stationary elderly test subjects produced ∼ 32% less heat flux compared to minors (mean: children = 13.9 mW/cm², adults = 11.4 mW/cm², elderly =  9.4 mW/cm²). This potentially correlates with an increase in thermal skin resistance with age (children = 494 cm² K/W, adults = 549 cm² K/W, elderly = 835 cm² K/W). The mean harvested power varied from 12.2 μW/cm² (elderly) to 26.2 μW/cm² (children) for stationary, and from 20.2 μW/cm² (elderly) to 69.5 μW/cm² (children) for active subjects inside of a building. The findings of this study can be used to better anticipate the available energy for different usage scenarios of thermal harvesters and optimize wearable systems accordingly.