Effect of Ambient Humidity on Thermal Sensation Using Seat Ventilation System

¹ Tokyo City University, 1-28-1, Tamadzutsumi, Setagaya-ku, Tokyo, 158-8557 Japan
² Graduate School of Tokyo City University, 1-28-1, Tamadzutsumi, Setagaya-ku, Tokyo, 158-8557 Japan

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

Thermal environments inside vehicles can be more extreme than those in buildings due to limited thermal insulation. During summer driving, cabin temperatures often exceed 40 °C, requiring prolonged HVAC operation to achieve thermal comfort. To improve cooling efficiency, seat ventilation systems have been introduced. These systems circulate air through small perforations in the seat to promote sweat evaporation and enhance body cooling. The effectiveness of this cooling depends not only on air temperature but also on humidity, since evaporation is driven by vapor pressure differences. This study investigates the relationship between air humidity and cooling performance in seat ventilation systems, with the goal of optimizing thermal comfort. Human participant experiments were conducted to measure skin temperatures at the back and waist and to record thermal sensation responses under varying conditions of air temperature and humidity. Humidity levels at the air outlet were also monitored. The results indicate that lower ambient humidity improves the cooling effect, as reflected by increased humidity at the system’s air outlet. However, if the humidity is too low, overcooling may occur, resulting in discomfort. These findings underscore the importance of carefully managing both airflow and humidity to maintain comfortable thermal conditions in vehicle cabins.