An experimental study of the thermoelectric properties of oriental hornet silks and their application in buildings

This paper investigates the thermoelectric and thermoregulatory properties of Oriental hornet silk. The larvae of the Oriental hornet produce silks, which it uses to create a silken cap at the end of a vertically orientated comb. It has been found that the silk caps also play a part in hornet nest thermoregulation. The nest of the Oriental hornet is maintained at a constant temperature of 28°C whilst the ambient temperature outside ranges from 20 to 40°C. Silk caps possess thermoelectric and thermophotovoltaic properties that help to regulate the temperatures in the nest by storing excess heat as an electric charge in the caps as temperatures rise and releases the energy as heat as temperatures fall. Controlled experiments have been carried out on silk cap samples in which we measured resistance, voltage and current during variations in temperature and relative humidity (RH). We have showed that in dry conditions, silk caps act as high resistance materials. The material therefore acted as a dielectric. We measured the charge and discharge characteristics and found that it behaved as a high performance capacitor. In humid conditions, silk caps acted as low resistance materials. The material therefore acted as a thermoelectric energy generator. Doping of the silk caps with LiCl reduced the resistance and increased thermoelectric generation in comparison to results found during high RH conditions. It was shown that resistance was temperature dependent and reached a peak between 25 and 32°C, which is thought to correspond with the glass transition temperature. We discuss how the principles could be applied to buildings and other applications. Energy harvesting is a growing field of study and by using variations in ambient conditions, such as temperature, RH, and solar irradiation, we could develop multifunctional structures for buildings integrated with high efficiency buildings, and so reduce reliance on distributed energy and conventional supply infrastructure.