Thermal Comfort of Older Adults in Hot Environments: Experimental and Numerical Investigation of Local Cooling Devices

Abstract

Older adults, as a vulnerable population, are more susceptible to heat-related mortality during heatwaves than younger individuals. In Finland, recent studies have highlighted this heightened risk. The room (without cooling systems) temperatures will exceed 32°C for about 3000 Kh. In addition, the declining income of the elderly also forces them to consider energy expenditure, thus facing more severe challenges. Some devices already on the market that can provide local cooling may help older people better maintain thermal comfort in hot weather. Compared with air conditioning, these devices are cheaper, more energy-efficient, easier to operate and more portable. However, there is little research on this topic. Thus, this thesis investigates the effectiveness of three types of local cooling devices in enhancing thermal comfort for older adults under various thermal environments. The research comprises four key components: 1) thermal responses of older adults in different thermal conditions; 2) changes in thermal responses after using three local cooling devices; 3) the physiological–psychological correlation of thermal sensation in older adults, and 4) modeling and validation of a novel personal cooling system. The results of the study showed that the neutral temperature of the elderly from northern Europe was 26 °C, their preferred temperature was 26.5 °C and the upper limit of the acceptable temperature was 28 °C. The lowest thermal acceptance rate was observed in environments with high temperature and relative humidity. At 28 °C (60%) and 29 °C (40%), the use of a table fan, evaporative cooling device, or air-cooled jacket could reduce the elderly's thermal sensation to neutral and make more than 80% of people accept the thermal condition. At 33 °C (40%) and 32 °C (50%), the use of an evaporative cooling device or aircooled jacket reduced thermal sensation significantly, but not to a neutral state. Although thermal acceptance rates increased after using all devices, they were less than 80%, except at 33 °C (40%), when evaporative cooling was used. Furthermore, all three devices performed better under conditions of lower relative humidity. Older adults' skin temperature in the head, limbs, and extremities has the strongest correlation with thermal sensation, and the thermal sensation in the head and torso exerts about 70% influence on overall thermal perception. Skin temperature and device usage had a complex causal relationship, and the cross-lagged effect between the two was the most significant at 5-minute intervals. The proposed novel local cooling system, which combined an evaporative cooling chair and a ventilated jacket can make older adults' thermal sensation reached to 0.5 in room at 33 °C. Meanwhile, it led to a notable 19 % reduction in electric energy consumption while maintaining similar elderly thermal sensation.